Cream of the Crop 1/Cream of the Crop 1.iso/PROGRAM/ANIVGA.ARJ/ANIVGA.DOC

Text File | 1991-11-17 | 131KB | 2,759 lines

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                        (English documentation)

            ┌─────────────────────────────────────────────┐
            │                   ANIVGA                    │
            │      a Sprite-Unit for TurboPascal V6.0     │
            │              by Kai Rohrbacher              │
            │                 Version 1.0                 │
            └─────────────────────────────────────────────┘


Purpose  : Animation of sprites on a VGA's 320x200x256 mode and
           TurboPascal V6.0
Author   : Kai Rohrbacher
           Germany
           Internet: [e-mail]
           FIDO    : 2:241/7503
Language : TurboPascal V6.0
Date     : May 1991

---------------------------------------------------------------------
Always remember: "I know my English spelling is bad, but if I used my
                  own language you probably couldn't read it at all."
                                                     -- Nico de Vries
---------------------------------------------------------------------

0. Table of contents
────────────────────

  1. Prélude: Legal Notices
  2. What is VGA?
  3. Features and Restrictions of ANIVGA
  4. "HELLO WORLD" - A First Example
  5. How ANIVGA works
  6. Tips, tricks and techniques
  7. Credits
  8. ANIVGA Reference Manual


1. Prélude: Legal Notices
─────────────────────────

Okay, the boring stuff first...

The author hereby disclaims all warranties relating to this software,
whether expressed or implied, including without limitation any implied
warranties of merchantability or fitness for a particular purpose.
I will not be liable for any special, incidental, consequential, indirect
or similar damages due to loss of data/damage to hardware or any other
reason, even if I have been advised of the possibility of such damages.

This programming toolkit is released as "freeware" by the author.
It is however copyrighted and all rights and ownership are kept with the
author. You may use it, copy it and give it to everybody as long as no
modifications are made  -- but don't try to sell it (or part of it)!

Nevertheless, all programs you realize with this software package may be
distributed freely - the only thing I ask you for is to mention the use
of this toolkit in your program and to send me a copy of your program.


2. What is ANIVGA?
──────────────────

ANIVGA is a powerful toolkit for the animation of sprites on any IBM (or com-
patible) with a VGA card installed.
It consists of one (big) TurboPascal V6.0-unit to be used by your applications
and some utilities to simplify its use:

ANIVGA.PAS   - the source code of the animation unit
MAKES.EXE    - a simple spritemaker program (requires a mouse)
GRAB.EXE     - a TSR-program to "grab" sprites from other graphics
UNLIB.EXE    - a utility to break apart a library of sprites back into
               its individual sprite files
DUMP_SPR.EXE - a "sprite dumper" which disassembles a (binary) sprite file into
               an ASCII-text
*.*          - documentation, examples, ...

Copy these files into your TurboPascal-directory and compile ANIVGA.PAS to
implement ANIVGA on your system - that's all.


3. Features and Restrictions of ANIVGA
──────────────────────────────────────

Some of ANIVGA's features are:

 - flickerfree animation by a "page-flipping" algorithm and using the
   vertical retrace signal
 - sprite movement in any increments you want
 - arbitrary background image for the animation
 - full use of the VGA's 256-color mode
 - several sprite display methods available:
   - sprites can be written normally (covering underlying figures)
   - sprites can be declared to be transparent with regard to the background
     or other sprites pixel by pixel
   - sprites can change their color depending on the underlying background
     image (-> shadow function)
 - display methods can be different for each sprite
 - pixel precise hit-detection routine built in
 - correct clipping of sprites at the screen boundaries
 - up to 32767 different sprites
 - up to 500 sprites may be simultaneously active
 - maximal size of each sprite = 64k
 - maximal size of all loaded sprites only restricted by available memory
 - works with virtual coordinates in the range -16000..+16000
 - thus simple creation of horizontal/vertical "scrolling" games
 - scrolling background image, too
 - several supporting routines to: drawing lines (with built in clipping-
   algorithm), points and graphic-text (incl. clipping), automatic heap
   management for loading of sprites, sprite libraries, background images,
   processor-speed adjustment,...

What ANIVGA does _not_ support:
 - EMS or XMS memory  (too slow)
 - resolutions other than 320x200x256  (compatibility question)


4. "HELLO WORLD" - A First Example
──────────────────────────────────

ANIVGA uses a non-standard 320x200x256 graphic mode, different from the BIOS-
mode $13, but there should be no problems with all truly compatible VGA cards.
To see if ANIVGA is compatible with your system and to get a first impression
of its ease of use, compile the following simple program (you can find it on
disk as file "EXAMPLE1.PAS"):

(Remember to copy and compile ANIVGA.PAS in your TurboPascal-Unit-directory
 first)

PROGRAM Example1;
USES ANIVGA,CRT;
CONST LoadNumber=42; {why not 42? - A "hello" to all Douglas Adam fans!}
      SpriteName='FLOWER.COD'; {Path and name of the sprite to load}
      Sprite1=0;
      Sprite2=5;
VAR ch:CHAR;
    collide:BOOLEAN;

BEGIN
 IF loadSprite(SpriteName,LoadNumber)=0
  THEN BEGIN
        CloseRoutines;
        WRITELN('Error: '+GetErrorMessage); halt(1)
       END;

 InitGraph;

 Color:=66;
 BackgroundLine(0,0,XMAX,0); BackgroundLine(XMAX,0,XMAX,YMAX);
 BackgroundLine(XMAX,YMAX,0,YMAX); BackgroundLine(0,YMAX,0,0);
 BackgroundOutTextXY(100,70,'Hello world!');

 SpriteN[Sprite1]:=LoadNumber;
 SpriteX[Sprite1]:=0; SpriteY[Sprite1]:=0;

 SpriteN[Sprite2]:=LoadNumber;
 SpriteX[Sprite2]:=XMAX SHR 1; SpriteY[Sprite2]:=YMAX SHR 1;

 WHILE KeyPressed DO ch:=ReadKey;
 Animate;
 REPEAT
  collide:=Hitdetect(Sprite1,Sprite2);
  if collide THEN BEGIN Sound(1000); Delay(5); NoSound END;
  if KeyPressed
   THEN BEGIN
         WHILE KeyPressed do ch:=UpCase(ReadKey);
         CASE ch OF
          'I':DEC(SpriteY[0]);
          'J':DEC(SpriteX[0]);
          'K':INC(SpriteX[0]);
          'M':INC(SpriteY[0]);
          'A':DEC(StartVirtualX,10);
          'S':DEC(StartVirtualX,10);
         END;
         IF POS(ch,'IJKMAS')>0 THEN Animate;
        END;

 UNTIL ch='Q';

 CloseRoutines;
END.

(Don't worry if you do not understand the whole program at once - it should
 only give you a first impression of ANIVGA's capabilities)
If you run this program (make sure that the sprite file FLOWER.COD can be found
by the program!) you should see a graphic consisting of two flowers, a rec-
tangle showing the screen boundaries and the words "Hello world" near the
middle of the screen.
You can move the top left flower by using the keys "I","J","K","M".
If you hit the other flower with the first one, the program will beep.
Try out what happens if you move across the two words in the middle: obviously,
the two leafs of the sprite behave somehow different: the black parts of left
leaf are "transparent" in that the writing shines through it, while the black
parts of the right leaf are "covering black".
But the writing (which is written in the background image) won't be destroyed.
As soon as you leave them, the words will be alright again.
Move the sprite to the very left screen boundary - and move it even more to
the left: you'll get the impression that it moves off the screen until it is
totally offscreen.
Hmmmm - how do we get it back? Sure, "K" will do, but press "A" instead: this
will "pan" the whole screen 10 pixels to the left (think of that as if you
could control an imaginary camera to slide to the left), "S" pans into the
other direction (note the restriction of the program to non-scrolling back-
ground at this point: the big rectangle and the words "Hello world" won't
move because they are part of the so-called "static" background image).
Now -using the "I","J","K" and "M" keys- bring back your sprite to the 2nd one
and let them collide. Press "A" a few times to scroll them both offscreen.
As you'll notice, the program will not stop beeping: it indicates that the two
sprites collide, even if they are not visible to you!
Okay, that should be enough for a first impression, so hit "Q" to quit the
program, if you've finished wondering... :-)

Run EXAMPLE2.PAS for a demonstration of "scrolling" background; the program is
much the same as EXAMPLE1, but uses four different "tiles" to build the back-
ground image. As before, you can use "I,J,K,M" to move your sprite along, but
this time, you may scroll the whole scene (incl. the background!) with the
"E,S,D,X" keys, too ("Q" quits, as before).

EXAMPLE3.PAS shows (an extremely) simple use of the "Display_SHADOW" mode to
display a graphical object: a sprite is used for its own shadow zone, simply by
redrawing it with a little horizontal and vertical offset.
Although this is a nice trick with many sprites (you don't have to design extra
shadow sprites this way), it doesn't always work: note that there is one area
in the flower which differs from what we would expect as shadow: this is
because ANIVGA assumes that everything between the left- and rightmost point of
a sprite belongs to the sprite's interior and will be drawn accordingly.
(To circumvent this, one would have to draw one (or even several) especially
 designed "shadow zone" sprites for the flower, but we'll come to these aspects
 later)
Pressing "P" draws 1000 randomly distributed points so you can better see the
shadowing effect for single points.
Finally, "C" copies part of the screen into memory (with GetImage() ) and
pastes it somewhere else (with PutImage() ) while clipping off at the screen
boundaries.

EXAMPLE4.PAS is an example how to use "sprite cycles": there are six images in
the sprite (library) file HANTEL.LIB which become "glued" together to form one
sprite cycle.
App. one hundred copies of this sprite are then animated on the screen with
maximum animation speed and again, you can scroll the whole screen area with
the keys "E","S","D","X". When you do, you will note that as more and more of
the sprites gets scrolled offscreen, the remaining sprites will rotate faster.
Pressing the space bar will toggle between fastest animation (no time limit)
and an animation rate of 200ms per frame.
You can play around with this value to find out an "optimal" time for your PC
and this program:

 very small: program will show the same symptoms as mentioned above (being
             faster for every sprite offscreen)
     .
     .
     .
 very big  : program will slow down even when all sprites are onscreen

Somewhere between lies a value where the animation doesn't get slowed down when
all sprites are onscreen (=max. work for ANIVGA), but stays at the same speed
for all other cases (=less work for ANIVGA).


5. How ANIVGA works
───────────────────

(It would be _impossible_ trying to cope every detail of ANIVGA, but I'm sure
 you will get the basic ideas of ANIVGA very soon.)

As already mentioned, the program uses a "tweaked" VGA-graphic mode: the VGA
is programmed in a way to give 4 graphic pages at a resolution of 320x200
pixels in 256 colors ("they said it couldn't be done, but here it is!..."),
numbered 0..3.
Page 0 and 1 are used for the display, page 2 holds the "normal" background
image and page 3 can contain so-called "tiles" which can be used to build a
huge background image in "scrolling" background mode.
The basic idea of the "page flipping" scheme used is that: do everything (era-
sing the old graphic page, draw sprites/lines/pixels/text) on a graphic page
invisible to the user while showing him a completed page on the screen.
Then, if finished, "flip" the page, thus making the new, completed page visible
and the old page to the invisible one. Now start creating the next image on
this new invisible page - and so on.
"Erasing" the old image means: overdraw it completely with the background image
stored in page 2 (or 3), so one could write in pseudo code:

   ...
  REPEAT
   show page 0 to user;
   fill (invisible) page 1 with contents of page 2;
   draw new sprites and all other stuff on page 1;
   show page 1 to user;
   fill (invisible) page 0 with contents of page 2;
   draw new sprites and all other stuff on page 0;
  UNTIL DOOMSDAY
   ...

You as the programmer doesn't have to think much about this mechanism, the
routines keep track of the page flipping automatically: the global variable
"PAGE" always holds the number of the page which is invisible (and thus:
the page to be drawn on). Therefore, we say that PAGE holds the "actual page"
number and 1-PAGE is the page visible to the user.
Most of the procedures and functions of the animation package adjust themselves
to the appropriate page; there are only a few situations where you have to be
aware of this mechanism, mostly when drawing pixels or to create special
effects.

The whole package is "table driven". That means, the interface to the user
consists of some tables in which you specify your sprites to be drawn:
You store into this tables which sprites to draw ("SpriteN[]") and their
coordinates (in "SpriteX[]" and "SpriteY[]").
After this, a call of the main routine "Animate()" gives back control to the
animation routines, which update the graphic screen accordingly:

...
REPEAT
 update SpriteN[]-table:
   deactivate sprite i by storing a "0" into SpriteN[i]   or
   activate a sprite k by storing k in an unused SpriteN[]-entry   or
   let all the other SpriteN[]-entries as they were last cycle
 FOR ALL SpriteN[i]<>0 DO
   IF SpriteN[i] should change its coordinates
     THEN update (SpriteX[i],SpriteY[i]) accordingly
 call Animate() to draw image and display it
UNTIL end-of-computer-life
...

You should notice that there are two kinds of "sprite numbers" which should
not be mixed up: one is a spriteLOAD number and represents a handle to the
(physical) sprite data, while the other (normally termed "sprite number") is
a logical number to address this sprite data.
In the pseudo code given above, "k" is the spriteLOAD number (it is a number
given at load time) and the index "i" in SpriteN[i] is the sprite number.
Note that "k" is a unique value: you can think of it as a NAME of the sprite
data loaded (e.g. you could name the FLOWER.COD - data as "123" when loading
it: there can't be another sprite with the same LOAD-number). On the other
hand, there could be a hundred flowers on the screen: just choose hundred
different sprite-table entries (=sprite numbers), e.g. SpriteN[100]..
SpriteN[199] and store "123" in each of them!
Whenever you are unsure if you (or I) are speaking of a "sprite number" or a
"spriteLOAD number", remember that:

 ■ A sprite number can hold values in the range 0..NMAX and is an index of
   the tables SpriteX[], SpriteY[] and SpriteN[].
 ■ A spriteLOAD number can hold values between 0..LoadMax and is assigned
   as a "name" to the sprites' physical loaded data; a "0" as load number is
   reserved for "inactivate sprite"


The world ANIVGA knows is 32000 pixels wide and high, numbered -16000..+16000
on each axis. Because your graphic screen consists of only 320 by 200 points,
(ranging from 0..XMAX and 0..YMAX in the x- and y-axis, respectively; (0,0) is
 the upper left corner, (XMAX,YMAX) the lower right one) you can only see a
small part of this world, but ANIVGA does not distinguish between the visible
and invisible parts of the world. If, for example, two sprites collide, the
routine "HitDetect()" will find out, even if this collision occurs offscreen.
Thus you can think of your graphic display being a "camera" to the real world:
your actions can take place everythere in this virtual world, but you see only
the part displayed by your camera; if you wish to see another part of your
world, you have to move this imaginary camera to that place.
In ANIVGA, you can do this by changing the values "StartVirtualX" and
"StartVirtualY" which hold the upper left corner of the visual window. As an
example, let (StartVirtualX,StartVirtualY) be (1000,500): then on your screen
you will see the part of the world which ranges from coordinates (1000..1319)
and (500..699) in X- and Y-directions, respectively.


6. Tips, tricks and techniques
──────────────────────────────

There would be a lot of things to say and most of them will be mentioned in the
following "Reference Manual". Nevertheless, it seems reasonable to repeat them
in a more concentrated form here, although this happens to make this chapter a
real topsyturvydom...

a) The ERROR-concept: if an error occurs in one of ANIVGA's routines, the
   global variable ERROR will be set accordingly. This gives you the freedom
   either to check this variable each time you called a routine - or ignore it
   for improved speed.
   As a rule of thumb, you should always check this variable while your program
   is still in the testing phase - and "comment out" these sections when you
   are through with debugging. (Conditional defines are great for that job!)
   Note that there are some routines that do not set ERROR at all (like Screen,
   GetPixel, PageGetPixel, PagePutPixel), either because in some special cases,
   "nice" tricks can be played with "faulty" parameters or because of severe
   speed improvements! For example, if you are going to read a 5000 pixel area
   from the screen with PageGetPixel(), it would be crazy to check 5000 times
   whether the "page" given to read from is valid or not.

b) Pixel-drawing routines: basically spoken, there are three sorts of graphic
   data objects in ANIVGA: sprites, pixels and background images.
   Because of ANIVGA's working scheme, all routines handling pixels (PutPixel,
   PagePutPixel, Line, PutImage,...) must be used in a special form:
   - If you use them to "draw" into the background page, this can only be done
     when using background mode STATIC (because in mode SCROLLING, the back-
     ground is stored in a compressed format one can't access directly).
   - Drawing into the background page in mode STATIC is fine (that's the main
     advantage of this mode compared with mode SCROLLING), and the best time to
     do it is _before_ calling Animate(), because changes to the background
     image will then be visible with the call to this routine.
   - Drawing "on the monitor screen" will be visible exactly for one animation
     cycle, that is: until the next call to Animate(). For this reason, you
     must do this changes _after_ calling Animate() and at the _visible_ page
     1-PAGE (not the _actual_ page PAGE itself).

     It is not that difficult as it may sound at first glance; for example:
     ...
     REPEAT
      read_user_inputs; compute_necessary_actions;
       do_all_changes_to_the_background_image;
       do_all_changes_to_the_sprites;
       Animate();
       do_all_changes_to_the_visible_screen; {e.g.: Line(0,0,XMAX,YMAX,1-PAGE)}
     UNTIL user_wants_to_end_application
     ...

     This way, after having called Animate(), the changes to the background
     (and your sprites) will be visible (because Animate() has generated an
     appropriate picture) and your changes to this image with the pixel-
     drawing routines will be visible "at once".
     That image will then stay visible until the next call to Animate().
     (Simply spoken, you let Animate() generate and display a picture and then
      do some changes to the picture while it is diplayed)
   - Because of unavoidable memory restrictions, ANIVGA can't store pixels
     drawn offscreen: if ANIVGA sees that points/lines lie outside the visible
     screen, it just does nothing at all; in other words, you can't draw a line
     outside the screen and "scroll it in" five minutes later! (You would have
     to define the line as a sprite instead, because sprites are the only
     objects stored independently).

c) Coordinates: Throughout all routines, ANIVGA works with _virtual_ coordi-
   nates (that is, values in the range xε[-16000..+16000], yε[-16000..+16000]),
   but sometimes you will have to address _absolute_ coordinates (in the range
   xε[0..XMAX], yε[0..YMAX]), so you have to transform virtual coordinates into
   absolute coordinates (or vice versa), which is _very_ easy:

   virtual coordinates -> absolute coordinates:
      Xabsolute := Xvirtual - StartVirtualX
      Yabsolute := Yvirtual - StartVirtualY

   absolute coordinates -> virtual coordinates:
      Xvirtual  := Xabsolute + StartVirtualX
      Yvirtual  := Yabsolute + StartVirtualY

d) Background / valid pages: Many routines expect a graphic page number as
   parameter. As mentioned under b), BACKGNDPAGE is valid only when you use
   background mode STATIC. Nevertheless, you can draw to this page even when
   you are using background mode SCROLLING without getting an error
   "Err_InvalidPageNumber" (although you are _strongly_ discouraged to do so)!
   That's because you can play some tricks on ANIVGA this way, provided that
   you do know _exactly_ what you (and ANIVGA) are doing, but this "feature"
   will probably be cut off in future versions of this program.
   (Note that this doesn't mean that you can't switch between STATIC and
    SCROLLING backgrounds during runtime! - It only says that you can't use
    the two background pages _in parallel_ (=at the same time)!)

e) Display objects at the same abolute screen position:
   Let us assume you want to display a score at the upper right corner of the
   screen; that's not hard when using STATIC background: just define your
   score as a sprite and choose an appropriate coordinate pair.
   In SCROLLING mode, your score would scroll away, too, so you must tie it to
   absolute screen coordinates, as said in c), but there is a simple rule which
   can be derived from the equation

      absolute_coordinate := virtual_coordinate - StartVirtual_value

   To ensure that the absolute (=screen) coordinate stays the same, you have to
   balance out changes done to the StartVirtual-variables like this: whenever
   you increase/decrease StartVirtual? by some amount delta, increase/decrease
   your score-coordinates by the same amount delta!
   (This results in: new_coord := virtual_coord±delta - (StartVirtual±delta)
    = virtual_coord - StartVirtual = old_coord    as wanted)

f) Displaying scores: another way to display a score without defining it as a
   sprite would be to simply draw it to the screen with the pixeldrawing rou-
   tines or OutTextXY():
    ■ draw it to the visible page (1-PAGE) each time after having called
      ANIMATE()
    ■ draw it to the background page BACKGNDPAGE
   The last method is applicable only in background mode STATIC and you have
   to restore the background image in the used area manually, but has the ad-
   vantage that you must redraw your score only when it really changed (instead
   of every animation cycle as with the first method). One way to accomplish
   that would be to use the GetImage() and PutImage() routines:
   ...
   build background image;
   use GetImage() to get a copy of the background area which will be overdrawn
   by the score;
   ...
   main_loop:
    IF new score has to be displayed
      THEN BEGIN
            use PutImage() to restore old background area underneath the score;
            use OutTextXY() to write new score into the background image
           END
   ...

g) Speed: It is hard to predict the speed of animations, because that is merely
   determined by the speed of your VGA card, not your computer's CPU clock
   rate! E.g., a program runs faster on my old AT (8MHz) than on a fast (25
   MHz) 80386 machine - only because of a better VGA card installed in the AT!
   Stated otherwise, if you use a computer with "enough" CPU-power, you won't
   have to think much about "should I use STATIC background instead of SCROL-
   LING for improved speed?", because it won't matter anyway!
   The break even point, where the VGA-card's bottle neck becomes the limiting
   factor depends largely on your application (and your VGA-card, of course),
   but as a rule of thumb, clock speeds faster than 12MHz won't improve your
   program speeds *linearly* any further:

        animation  ^            ______
        speed      │     ___----
                   │    /
                   │  /
                   │/
                   ┼─────┬───────────>  clock rate
                         break-
                         even point

   Note that your programs will still profit from faster CPU's, but that is due
   to faster computation of all routines not limited by accessing the video
   RAM; even on the fastest clones, the IBM-bus-clock-rate is not faster than
   10MHz  -- and this limits accessing the VGA card: sad, but true...

g) DMA access: Quite a long time, I tried to speed up animation rates by using
   the DMA-chip in parallel to the CPU: while the CPU is running your program,
   the DMA should move around memory.
   Unfortunately, I had to find out that most computers don't like DMA memory-
   to-memory transfers at all and those who do don't work when addresses used
   reference the video RAM area (I can't explain why this is the case).
   If someone out there has successfully worked with the DMA chip this way, I
   would be glad to know!


7. Credits
──────────

Honour to whom honour is due! Although most of the routines are mine, two of
the utility programs (also written in TP6.0) use stuff from other Freeware
authors:

- The GRAB-utility uses Ken Pottebaum's TSR-unit TSRUNIT.ZIP       and
- The MAKES-designer uses John Bridges' BGI-driver SVGA256.BGI (for the VGA's
  320x200x256 mode $13) from his SuperVGA-driver package SVGABGI3.ZIP

(Both programs are available at the SIMTEL20-servers)

Thanks to them for supporting the Freeware-concept, their spirit made it
possible to distribute this program as Freeware, too!


8. ANIVGA Reference Manual
──────────────────────────

This reference manual lists all routines, variables, constants and a lot of in-
formational stuff concerning ANIVGA in alphabetic order.
Don't get frightened about the amount of informations given; in normal appli-
cations you will need only a few of them!


ABSOLUTE COORDINATES - information
──────────────────────────────────

See       : coordinates


Animate - procedure
───────────────────

Function   : Performs a complete animation cycle

Declaration: {$F+} PROCEDURE Animate {$F-}

Description: A call to Animate() clears the invisible graphic page by copying
             the contents of the background image into the actual drawing
             page (specified by variable PAGE).
             Then all active sprites (SpriteN[i]<>0) in the visible window
             (determined by StartVirtualX and StartVirtualY) are drawn in the
             style and at the coordinates given by the user.
             After that, the routine waits for a vertical retrace to reprogram
             the VGA adapter to flip the display pages, making the completed
             image visible and changes PAGE to point to the new, invisible
             graphic page.
             Finally, the procedure looks how much time passed since the last
             animation cycle and if this time is less than that set by
             SetCycleTime(), the program waits accordingly.

Note       : This procedure is the kernel routine which has to be called every-
             time when you have set all data for a new animation frame.

See also   : PAGE, SetCycleTime, StartVirtualX, StartVirtualY


BackGndPage - constant
──────────────────────

Function   : Holds the page number of the backround page

Declaration: CONST BACKGNDPAGE=2;

Description: When using background mode STATIC, BackGndPage specifies the page
             number of the background image for the animations to be used.

Note (!)   : Use of this constant only makes sense when using background mode
             STATIC!

See also   : ScrollPage, Background


Background - information
────────────────────────

The term "background" specifies a graphic image in front of which all anima-
tions take place.
There are two sorts of background in ANIVGA: SCROLLING background and STATIC
background, which you choose with SetBackgroundMode().

As its name states, a STATIC background cannot be scrolled: it consists of a
320x200 pixels picture.
This background picture is stored in the graphic page numbered BACKGNDPAGE.
At the very start of every animation cycle, the routine Animate copies that
picture into the actual drawing page, thus erasing old stuff on that page and
building the basis for the new image.
As a normal bitmap picture, it is 320x200=64000 bytes in size. If you use the
GRAB-Utility or the WritePage()-Routine to save an image, a three byte header
is put ahead of the information, thus extending the size to 64003 bytes.

The second background sort is called SCROLLING: like ANIVGA's virtual coor-
dinates, you can define a huge background image and scroll over it.
Unfortunately, it is impossible to hold a complete background picture in
memory: you would need 32000*32000=1024000000 bytes RAM (!) to do that.
Instead, ANIVGA uses a "tiling" mechanism: tiles are small pictures (16x16
pixels) which can be combined freely to build the background image.
You can use up to 256 different tiles and "pin" them on an background area of
up to MaxTiles (=10000) tiles; everything outside of this background area will
be assigned to tile no. 0 automatically.
For example, let us assume that you use only scrolling in the y-coordinate
axis, 16 screens in total: thus, your x-coordinates reach from 0 to 319 and
your y-coordinates from 0..(16*200-1)=5119, which gives an area of 320*5120
=1638400 pixels.
This is equivalent to (320/16)*(5120/16)=20*320=6400 tiles (remember: each
tile consists of 16x16 pixels!).
So you would define the scroll range for the background area needed with
SetBackgroundScrollRange(0,0,319,5119) and start "painting" your background:
You could design up to 256 different tiles and use them to assemble your
background image (=those 6400 tiles).
Most often, only a few are needed, because the background image isn't that
dramatically different all over the place. For simplicity, let's assume that
you need only 20 different tiles, numbered 0..19 respectively in the following
order to build your background image:

  (0,0)                                                         (319,0)
    ┌────────┬────────┬────────┐         ┌────────┬────────┬────────┐
    │        │        │        │         │        │        │        │
    │   0    │   1    │   2    │   ...   │   13   │   14   │   15   │
    │        │        │        │         │        │        │        │
    ├────────┼────────┼────────┤         ├────────┼────────┼────────┤
        .        .        .                  .        .        .
        .        .        .                  .        .        .
        .        .        .                  .        .        .
    ├────────┼────────┼────────┤         ├────────┼────────┼────────┤
    │        │        │        │         │        │        │        │
    │   0    │   1    │   2    │   ...   │   13   │   14   │   15   │
    │        │        │        │         │        │        │        │
    └────────┴────────┴────────┘         └────────┴────────┴────────┘
  (0,5119)                                                      (319,5119)

Now all you have to do is to tell ANIVGA that layout with the PutTile command:

 {assuming SetBackgroundScrollRange(0,0,319,5119) has been set}
 number:=0;
 y:=0; {better: y:=BackY1}
 REPEAT  (things would become easier if Pascal would know a STEP-command...)
  x:=0; {better: x:=BackX1}
  REPEAT
   PutTile(x,y,number);
   number:=(number+1) MOD 16;
   inc(x,16);
  UNTIL x>319; {better: x>BackX2}
  inc(y,16);
 UNTIL y>5119; {better: y>BackY2}

That's it! (It is better to use the (global defined) "Back..."-variables, set
by the former SetBackgroundScrollRange()-call, because ANIVGA has to adjust
values on multiples of 16, see SetBackgroundScrollRange()/Back?? for more
details).

So then, why should one use STATIC backgrounds after all when there is such a
powerful instrument like SCROLLING backgrounds?
There are two simple answers: speed and simplicity! - First, SCROLLING back-
grounds take a lot of work to compute, which slows down animations (unless you
have a fast machine, because then the VGA's memory access time becomes the
limiting factor). Second, it is easy to do some "tricks" on static backgrounds:
draw a line in the static background page and >zap!< starting with the next
animation cycle, it will be visible for all times. Stated otherwise, when using
scrolling background, you cannot use drawings to the background image, because
it simply doesn't exist explicitly, you are restricted solely to "tiles" and
"sprites"! (On the other hand, you can play nice tricks on scrolling background
by changing single tiles...)
So consider carefully what mode you are going to use for your application!

See also   : BACKGNDPAGE, BACKGNDADR, WritePage, LoadPage, WriteBackgroundPage,
             LoadBackgroundPage, SetBackgroundMode, LoadTile, Tile


BackgroundGetPixel - function
─────────────────────────────

Function   : Reads a background pixel's color

Declaration: {$F+} FUNCTION BackgroundGetPixel(x,y:INTEGER):BYTE; {$F-}

Description: This routine will return the color value of the specified point
             with virtual coordinates (x,y) in the background image.
             If the corresponding absolute coordinates lie outside the screen,
             zero (= black) will be returned.

Note       : Use of this routine works only when using background mode STATIC!
             It might look strange to use virtual coordinates then, although
             the background is said to be static (= non-scrollable) and hence
             restricted to absolute coordinates anyway, but it is often con-
             venient to use an uniform notation and it is easy to convert co-
             ordinates accordingly (see "coordinates" for more about that).

See also   : coordinates, GetPixel, PageGetPixel


BackgroundLine - procedure
──────────────────────────

Function   : Draws a line on the background page

Declaration: {$F+} PROCEDURE BackgroundLine(x1,y1,x2,y2:INTEGER); {$F-}

Description: To draw a line on the background page (thus alterating the back-
             ground), you can use this procedure. Like the similiar Line()-
             routine, it uses virtual coordinates, too.
             If necessary, the line will be clipped down to its visible part
             (using a special Sutherland-Cohen algorithm).

Note       : Use of this routine only makes sense when using background mode
             STATIC!

See also   : Line, coordinates


BackGroundMode - variable
─────────────────────────

Function   : Holds the actual choosen background mode

Declaration: VAR BackgroundMode:BYTE;

Description: Using SetBackgroundMode(), you can select one of the possible
             background modes STATIC or SCROLLING. BackGroundMode stores this
             value.

Note (!)   : Only read this value, never change it directly!

See also   : Background, SetBackgroundMode


BackgroundOutTextXY - procedure
───────────────────────────────

Function   : Writes a textstring to the background page BACKGNDPAGE

Declaration: {$F+} PROCEDURE BackgroundOutTextXY(x,y:INTEGER; s:STRING); {$F-}

Description: This routine is exactly the same like OutTextXY() (see there), but
             it writes the string into the background page (so it will be visi-
             ble permanently).

Note       : Use of the routine only makes sense if STATIC is used as
             background mode.

See also   : GraphtextColor, GraphtextOrientation, GraphtextBackground,
             OutTextXY, background


BackgroundPutPixel - procedure
──────────────────────────────

Function   : Plots a point into the background page

Declaration: {$F+} PROCEDURE BackgroundPutPixel(x,y:INTEGER; color:BYTE); {$F-}

Description: (x,y) specify the virtual coordinates of the point to be drawn in
             color "color". If this point lies onscreen (i.e.: its _absolute_
             coordinates are between (0,0)..(319,199)), it will be drawn on the
             background page BACKGNDPAGE (and become visible starting with the
             next animation cycle).

Note (!)   : - Use of this routine makes sense only when using background mode
               STATIC!
             - This routine works with virtual coordinates! - Although this
               seems silly at first glance (because in STATIC mode, background
               coordinates are always restricted to (0,0)..(319,199)), it
               appears to be handy in many situations. If you actually want to
               address points absolute coordinates (a,b), you can call this
               routine with coordinates (a+StartVirtualX,b+StartVirtualY)
               instead.
             - Because of ANIVGA's working scheme, you probably want to call
               this routine _before_ calling Animate(), so that changes of the
               point will be visible as soon as possible.

See also   : PutPixel, PagePutPixel, background, coordinates, How ANIVGA works


BACKX1, BACKX2, BACKY1, BACKY2 - variables
──────────────────────────────────────────

Function   : Hold the background image boundaries in background mode SCROLLING

Declaration: BackX1,BackY1,BackX2,BackY2:INTEGER;

Description: When background mode SCROLLING is to be used, you have to define
             a scrolling area (with SetBackgroundScrollRange()). Due to inter-
             nal management restrictions of ANIVGA, the boundaries of this area
             must fall on coordinates which are multiples of 16 ("on a grid
             with mesh 16").
             If the values you supply don't fulfill this restriction, ANIVGA
             adjusts them automatically to do so and stores them to these
             variables for further use.

Note       : The only reason these variables are visible to you are that it
             could be necessary for you to notice adjustments ANIVGA did;
             so: only read this values, never change them directly!
             (Look at "background" for an example).

See also   : background


CloseRoutines - procedure
─────────────────────────

Function   : Terminates ANIVGA

Declaration: {$F+} PROCEDURE CloseRoutines; {$F-}

Description: Calling this routine switches back from ANIVGA's special graphic
             mode into the graphic or text mode previously set.

Note       : This should always be the last call to a routine of ANIVGA in your
             programs.

See also   : InitGraph


COLLISION-DETECTION, CONCAVE, CONVEX - information
──────────────────────────────────────────────────

A graphical figure can be classified by its outline into one of two groups,
called "concave" or "convex" figures.
To motivate this mathematical notion >eh, don't get frustrated...<, regard
your sprite only given by its "outmost" points, which connected together shape
the figures boundaries.
The figure is called "convex" :<=> every pair of arbitrarily choosen points
on this boundary build a line which is totally inside (or at least on the
boundary of) the figure:
  ┌──────┐ This rectangle is "convex", because whenever you choose two points
  │      │ on its boundaries and connect them, the resulting line lies com-
  └──────┘ pletely inside (or on the boundary) of the rectangle itself.

  ┌──────┐ On the other hand, this figure would be "concave", because if you
  └─┐  ┌─┘ choose the top-right and bottom-right corner (say) and connect them,
  ┌─┘  └─┐ then the middle part of the resulting vertical line lies outside the
  └──────┘ figure.

That is (in a very lax form) the _mathematical_ definition of these terms, but
ANIVGA completely deals with either horizontal or vertical lines, so that an
extension of these terms can be made:

A sprite is called "horizontal concave" ("vertical concave"), if a horizontal
(vertical) line connecting two points of the sprite's boundary can be found
so that parts of this line lies outside the sprite; if the sprite is not hori-
zontal (vertical concave), it is "horizontal convex" ("vertical convex").

In that sense, the second of the figures above is "vertical concave", but
"horizontal convex"!
(Notice that figures which are concave in the pure _mathematical_ sense are
 sometimes treated as convex by this definition, as this cross:)
    ┌─┐     (If you use either a horizontal or vertical "scan line" sweeping
  ┌─┘ └─┐    throughout the cross, there will be never more than one part of
  └─┐ ┌─┘    the "scan line" which belongs to the figure; you can use this
    └─┘      principle as a second definition for horizontal/vertical convex)

This terminology comes in handy when describing some mechanisms of ANIVGA: a
sprite is drawn LINEwise. For this, every point between the leftmost and right-
most point of a sprite's line is considered to be an _inner_ point of the
sprite, thus ANIVGA assumes a horizontal convexity! If your sprite isn't, like
this one...
  ┌─────┐  ...and the points between the two "legs" of this sprite shall still
  │ ┌─┐ │  be treated as "transparent" (assuming they have been defined with
  │ │ │ │  color "black" (=0)), you must use display mode "Display_NORMAL",
  │ │ │ │  because the "Display_FAST" mode would treat them as belonging to the
  └─┘ └─┘  sprite itself and draw them as "covering" black.

(To state it otherwise: whenever your sprite is (at least) horizontal convex
 and you don't need the feature of transparent parts inside the sprite, you
 can use the "Display_FAST" mode without any loss of accuracy in the sprite
 display)

Tip: the spritemaker program MAKES allows to display a sprite's horizontal
boundaries, which makes it easier for the beginner to decide about that
figure's convexity. But whenever you are unsure, you still can use mode
"Display_NORMAL" for drawing it.

---

Things get a bit more tough when deciding if two sprites collide or not (which
is an important task): in difference to many sprite toolkits, ANIVGA doesn't
use a "mask" approach, which makes sprites big and collision detection slow.
Instead, ANIVGA uses a sprite's outline to decide whether two sprites collide.
For that, it computes for every line (column) of the overlap region of the
sprites' surrounding rectangles, whether the sprites overlap horizontally
(vertically) and says "collision!" only if there are intersections in both
directions. In pseudo code:

IF smallest_box_around(sprite1) doesn't intersect smallest_box_around(sprite2)
 THEN no_collision
 ELSE BEGIN
       compute the lines and columns for which the 2 sprite rectangles overlap
       FOR every such line compare -with the help of the sprite boundaries- if
        the corresponding lines overlap
       FOR every such column do the same check
       ONLY_IF there is an intersection in at least one line AND one column
        THEN collision!
        ELSE no_collision
      END

If you think a byte (=8 bits...) about this algorithm, you'll see that it can
lead to misdetection, in that the algorithm says "collision!", although there
is none (but it still guarantees that if there _is_ a collision, the alg. will
detect it) as in the following example:
          ┌─────┐
          └───┐ │
   ┌────────┐ │ │
   │ ┌────┐ │ │ │
   │ │ ┌─┐│ │ │ │  <─ In this line there is a "horizontal collision" (that is,
   └─┘ │ │└─┘ │ │     the two sprites overlap in their horizontal dimension)
       │ └────┘ │
       └────────┘  ┌─ In this column there is a "vertical collision"
           ^───────┘

To state things without a proof here, such an (unavoidable) misdetection is
only possible, if at least one of the two sprites is neither horizontal nor
vertical convex!!!

Even then, it takes special constellations (as the one above) to produce such
an error, so that in praxis, it is very unlikely for such an error to occur.


Color - variable
────────────────

Function   : Determines the actual drawing color

Declaration: VAR Color:BYTE;

Description: Various drawing routines use this global variable to determine
             which color should be used.

Note       : ANIVGA uses the standard color table of the 256-color mode $13.

See also   : -


ColorTable - type
─────────────────

Function   : Supply a data type for self-defined "Shadow Tables"

Declaration: TYPE ColorTable=ARRAY[0..255] OF BYTE;

Description: If you want to use a different color look-up-table for your
             sprites in display mode Display_SHADOW than can be achieved with
             SetShadowTab(), you must build a table like this.
             Each entry gives the color which should be used to replace the
             original color with that index, i.e.: if c is of type ColorTable
             and c[5]=9, this means that every point of your sprite which is to
             be drawn over a pixel with color 5 should replace that pixel with
             color 9.
             You can find an example how to activate such a "home-brew" table
             at "ShadowTab".

Note       : -

See also   : ShadowTab, SetShadowTab, Display modes


COORDINATES - information
─────────────────────────

ANIVGA has to deal with two kinds of coordinates: "virtual" and "absolute" ones.
An absolute coordinate lies in the range 0..319, 0..199 for the x and y values,
respectively. It names a unique point on your graphic screen.
However, ANIVGA doesn't restrict animations to take place on the visible
graphic screen: its routines deal with coordinates in the range -16000..+16000
in each direction, called "virtual coordinates".
The picture you view while ANIVGA's routines are running is a window of that
virtual screen, 320 points wide and 200 points high.
Naturally, the graphic hardware only knows absolute coordinates and thus,
ANIVGA has to transform virtual in absolute coordinates. It does this with the
help of the two variables StartVirtualX and StartVirtualY which together speci-
fy the starting point of the upper left corner of your actual screen window;
e.g. if (StartVirtualX,StartVirtualY) was (1000,2000) then you would look at
the part of ANIVGA's world which consists of the 320x200 region with the coor-
dinates xε(1000..1319) and yε(2000..2199).
Note that there is one severe restriction, though: because it is absolutely
impossible to hold a complete "virtual" screen bitmap for ANIVGA's world in
memory (it would need app. 1GB RAM!), all drawing commands only take place on
the visible screen.
This means that you can't draw lines, points or any other objects which are
_not_ sprites outside the visible window that become visible, when you scroll
your window over to that part of the virtual screen. For example, if you draw
a point somewhere outside your visible window (say at (-10000,1234) while your
visible window starts at (500,900)) and pan to that region afterwards (by set-
ting (StartVirtualX,StartVirtualY)=(-10100,1200) or something like that), you
won't see that point: it is stored nowhere.
(The only way to circumvent this is to define the point as a sprite and set its
 coordinates (SpriteX[],SpriteY[]) to (-10000,1234), because sprites are the
 only objects which the system stores!).

More general:
Because there is _no_ complete virtual screen, all information drawn outside
the coordinate range visible at the moment will be lost and all information
read in from these "offscreen" pixel positions will be zero (= black).
For that reason it may seem strange for some routines that were restricted in
their use to the "real" (= absolute coordinate) screen region to use virtual
coordinates inspite (e.g.: GetImage, BackGroundGetPixel,...), but this was done
intentionally, because it leaves room for further improvements: if it should be
possible some day to store a complete virtual screen image, there will be no
changes necessary in ANIVGA's syntax.
Meanwhile, it is simple to transform absolute and virtual coordinates into each
other whenever necessary, using the following equivalence:

  virtual X-coordinates - StartVirtualX = absolute X-coordinates
  virtual Y-coordinates - StartVirtualY = absolute Y-coordinates

As a result: virtual coordinates lie in the range -16000..+16000, the start of
the visible part is defined in StartVirtualX and StartVirtualY and only sprites
can be "scrolled in" into the visible screen, while all other objects are
"lost".


Display modes - information
───────────────────────────

ANIVGA is able to display a sprite in several "modes". This describes how the
sprite's data should be handled when drawing the sprite to the screen. Up to
now, there are three modes:
 - Display_NORMAL
 - Display_FAST
 - Display_SHADOW
This mode is linked to a sprite's physical data by creation of the sprite with
the spritemaker program (and defaults to Display_NORMAL), but can be altered
once the sprite is loaded into memory with the procedure SetModeByte().

Note that the display mode information is part of the _physical_ sprites (that
is, the memory image of the bytes loaded at the beginning), not the _logical_
sprites (the "handles" in the SpriteN-array to this physical data). For that
reason, a change of the display mode of a sprite with spriteLOAD number 123
(say) will affect _all_ sprites of type 123 (= all entries in SpriteN[] with
value 123). This is intended, because the display mode is a piece of informa-
tion reflecting the sprite's physical structure.

In mode "Display_NORMAL" you can think of a sprite as a picture with holes at
the places where its pixels have color 0: when displayed, all the parts of the
sprite with color<>0 will cover (paint over) the screens original pixels, but
the pieces with color=0 will act like "window panes": the original contents of
the screen remain visible there.
This mode is useful for all kinds of sprites which have such opaque holes in-
side themselves: cars/planes/houses or other objects with window panes, but
also all "concave" sprites. Note that black, covering parts must be realized
with a dark color<>0, for example color 16.

"Display_FAST" is a bit (but not that dramtically) faster than the last method,
because it doesn't know of a special color: all sprite data is treated equally
and stored to the screen at once. For that, all parts of the sprite are
covering. (But note that a sprite consists only of the points inside and on its
boundaries: all the points of the smallest box surrounding it -that is the way
a sprite is stored- doesn't matter).
You will use this mode whenever you have sprites which meet the following re-
quirements: they are "convex" and don't have any transparent parts inside them-
selves.

"Display_SHADOW" is a tribute to the fact that one often needs some kind of
shadowing to give the impression of an freefloating object or other pseudo
3D-effects. In this mode, the sprite's real colors are insignificant, only its
boundaries and the actual contents of the screen where the sprite shall be
drawn are important. The color of every sprite point is determined by the color
of the appropriate screen point. The color of these points are translated by
the lookup table ShadowTab into darker ones.
If you want to give a sprite a shadow zone, then you must divide your sprite
into two ones: one building the sprite itself and a second one to realize only
that shadow area, and compose them with appropriate coordinates.

Technically spoken, there are short code areas in ANIVGA's routines reserved in
which the right piece of code to transfer/interpret the sprite's data become
copied, when not already there. For optimal performance it is wise to group the
entries in SpriteN[] such that adjacent sprite entries share the same display
method.

See also   : convex, concave


DUMP_SPR - utility
──────────────────

(This is surely a tool for all those hackers among us...)
If you want to take a closer look at a sprite's data, you don't have to fiddle
around with DEBUG or the like, just use this sprite dumper: it takes a (binary)
sprite file (*.COD or *.LIB) and disassembles it into readable ASCII-text.
You can redirect the output to a file or printer, e.g.:

 DUMP_SPR mysprite.cod >mysprite.txt

would dump the sprite file "mysprite.cod" to the ASCII-text file "mysprite.txt"
for further usage.
Note that DUMP_SPR creates a format which will be understood by assemblers like
MASM or TASM so that you can reassemble the files to get a binary sprite file
once again!


ERROR - variable
────────────────

Function   : Holds the code of the last error which occured

Declaration: VAR ERROR:BYTE

Description: If an error occurs while executing one of its routines, ANIVGA
             terminates that routine and sets ERROR accordingly to reflect that
             error.
             You can use GetErrorMessage() anytime to get more information,
             which error occured.
             It is your responsibility to check if such an error occured and
             react in an appropriate way.
             For the possible values and their descriptions returned by
             GetErrorMessage, see there.

Note (!)   : - After processing an error, you have to reset the variable back
               to Err_None yourself"
             - In respect of future extensions, you should treat every value
               <> Err_None as an error
             - The most frequented routine Animate() doesn't produce any
               errors, neither do several other procedures. As a basic rule,
               all routines which have to do with file I/O have to be checked.
             - ERROR is initialized with Err_None

See also   : GetErrorMessage, InitRoutines


FillBackground - procedure
──────────────────────────

Function   : Fills the background page with the specified color.

Declaration: {$F+} PROCEDURE FillBackground(color:BYTE); {$F-}

Description: The given value is written into the whole graphic page BACKGNDPAGE
             and thus defines the picture before all animations take place to
             have one color.

Note       : Use of this routine only makes sense when using background mode
             STATIC!

See also   : Background, BACKGNDPAGE, BACKGNDADR, GetBackgroundFromPage,
             LoadBackgroundPage


FillPage - procedure
────────────────────

Function   : Fills a graphic page completely with a given color

Declaration: {$F+} PROCEDURE FillPage(pa,color:Byte); {$F-}

Description: If you want to paint a complete page uniformly with one color,
             then this will be the fastest method to do it: specify the graphic
             page (0,1 or BACKGNDPAGE (=2)) in "pa" and the color to be used in
             "color".

Note       : - Although possible, you are strongly discouraged to use this pro-
               cedure in background mode SCROLLING (i.e.: pa=SCROLLPAGE (=3) as
               page number), because the background is treated completely dif-
               ferent!
             - Remember also that changes to one of the drawing pages (0 or 1)
               have to be applied _after_ calling Animate and will be visible
               for exactly one animation cycle, whereas changes to the back-
               ground page remain permanent (and are best done _before_ calling
               Animate, although that's not peremptory).
             - This routine is great to produce "flashing" screens: apply it to
               1-PAGE (the visible page).
             - Possible ERROR-values returned are Err_InvalidPageNumber

See also   : background, How ANIVGA works, LoadPage, LoadBackgroundPage,
             GetBackgroundFromPage


FontOrient, FontHeight, FontWidth - type/constants
──────────────────────────────────────────────────

Function   : Supply some additional data about the internal font

Declaration: TYPE  FontOrient=(horizontal,vertical);
             CONST FontHeight=6;
                   FontWidth=6;

Description: The internal font used for displaying graphic text (OutTextXY(),
             BackgroundOutTextXY()) can be displayed either horizontally or
             vertically; use of the TYPE FontOrient simplifies that.
             To compute the width/height of a text, the constants FontHeight
             and FontWidth can be used, which specify the size of one letter.

Note       : -

See also   : OutTextXY, BackgroundOutTextXY


GetBackgroundFromPage - procedure
─────────────────────────────────

Function   : Take over one of the drawing pages as background image

Declaration: {$F+} PROCEDURE GetBackgroundFromPage(pa:Byte); {$F-}

Description: Specify the graphic page (0 or 1) from which the image should be
             "captured" and the routine will copy its contents into the back-
             ground page BACKGNDPAGE (=2) as new background image.

Note       : - Use of the routine only makes sense if STATIC is used as
               background mode.
             - Possible ERROR-values returned are Err_InvalidPageNumber

See also   : LoadBackgroundPage


GetErrorMessage - function
──────────────────────────

Function   : Returns a description of the last error occured

Declaration: {$F+} FUNCTION GetErrorMessage:STRING; {$F-}

Description: Although you can use the ERROR variable directly to evaluate any
             error and inform the user about it, it is often more comfortable
             to let ANIVGA do that: GetErrorMessage will give you a string
             describing the last error which occured in words.
             The possible string contents and the corresponding ERROR values
             are:

              Err_None: 'No Error'
               No error occured during the routine; this is the variable's
               initial value

              Err_NotEnoughMemory: 'Not enough memory available on heap'
               The program couldn't load sprites or other data to the heap

              Err_FileIO: 'I/O-error with file'
               There was an error reading the file; either the file doesn't
               exist at the path given or it is damaged

              Err_InvalidSpriteNumber: 'Invalid sprite number used'
               This error occurs if you try to load a sprite with a sprite
               loadnumber not in the valid range 1..LoadMAX

              Err_NoSprite: 'No (or corrupted) sprite file'
               While attempting to interpret the data just read in, ANIVGA
               found the data not to be in the expected format; either because
               you used a wrong data file or it is damaged

              Err_InvalidPageNumber: 'Invalid page number used'
               There are four graphic pages, numbered 0..3. Page 0 & 1 are
               used for the animation itself, page 2 ("BACKGNDPAGE") holds the
               static background image and page 3 ("SCROLLPAGE") is reserved
               for the scrollable background information

              Err_NoVGA: 'No VGA-card found'
               The animation package needs a VGA (or compatible) graphic card
               but couldn't find one

              Err_NoPicture: 'No (or corrupted) picture file'
               The background picture file ANIVGA should load has not the ex-
               pected size/format or a DOS-error occured while attempting to
               access the data

              Err_InvalidPercentage: 'Percentage value must be 0..100'
               If you set the colortable for the shadowing effects of sprite
               display mode Display_SHADOW, you must use a percentage value
               giving the remaining brightness of the colors in the shadow
               areas, which must be in the range 0..100%, of course

              Err_NoTile: 'No (or corrupted) tile/sprite file'
               There was an error loading the specified sprite file(s) and
               interpreting them as background tiles. Most often this occurs
               because the sprite doesn't meet the requirement to be a multiple
               of 16 points in its x- and y-directions!

              Err_InvalidTileNumber: 'Invalid tile number used'
               There may be only 256 background tiles, numbered 0..255

              Err_InvalidCoordinates: 'Invalid coordinates used'
               The virtual background coordinates you use must lie in the range
               (BackX1,BackY1)..(BackX2,BackY2), which has been specified with
               SetBackgroundScrollRange()

              Err_BackgroundToBig: 'Background too big for tile-buffer'
               ANIVGA's tile buffer can hold no more than MaxTiles (=10000)
               tiles, that is an area of 10000*16*16 pixels². Check the area
               you specified in your SetBackgroundScrollRange()-call!

              Err_InvalidMode: 'Only STATIC or SCROLLING allowed here'
               The only background modes ANIVGA knows are STATIC and SCROLLING

              Err_InvalidSpriteLoadNumber: 'Invalid spriteload number used'
               spriteLOADNumbers must lie in the range 0..LoadMAX; when you
               get this error, you probably confounded a spriteLOADnumber with
               a spritenumber

              (else): 'Unknown error'
               If ERROR has none of the above values, this string will be
               returned; this should never happen, though.

Note       : Calling GetErrorMessage won't set back the ERROR variable either;
             you must do that explicitly!

See also   : ERROR


GetImage - function
───────────────────

Function   : Makes a copy of the specified screen region

Declaration: {$F+} FUNCTION GetImage(x1,y1,x2,y2:INTEGER;pa:BYTE):POINTER; {$F-}

Description: - This function works much the same as its equivalent in Turbo-
               Pascal: (x1,y1) and (x2,y2) define the upper left and lower right
               corners of the screen part to save, but now these coordinates are
               _virtual coordinates_, the routine reserves the memory needed to
               hold the copy itself and you can specify the graphic page, from
               which the image is to be taken (pa=0,1 or BACKGNDPAGE (=2) ).
             - As result you get a pointer to the start of the saved image,
               which can be used with PutImage().
             - If there is not enough memory available or the specified part of
               the screen lies completely outside the visible screen, NIL is
               returned.
             - Besides that, there are 5 global variables which are set accor-
               dingly:
               was_cut:BOOLEAN = TRUE/FALSE, if the image had to be _partially_
                       clipped (if the specified image is totally offscreen,
                       was_cut stays at FALSE!)
               left_cut, right_cut, top_cut, bottom_cut:WORD  hold the size how
                       much had to be clipped off at the boundaries; these
                       values are only set when was_cut=TRUE
               (If you wonder about this odd definitions: GetImage was intended
                to work only with the visible screen (that is: with _absolute_
                coordinates): together with its counterpart PutImage(), you can
                copy a part of the screen to another part or page. In that case,
                you do not have to fiddle around with clipping: just issue a
                GetImage() and use PutImage() to paste this block elsewhere.
                But there may be some applications, when you cut out part of
                the screen and think you got the complete graphic figure you
                wanted, although (because of the use of virtual coordinates and
                your figure being partially offscreen) you got only part of it.
                Checking "was_cut" informs you about such a partial clipping.
                If your figure is completely offscreen, that is a special case:
                it depends on your application whether this should be treated
                as being okay or not; if you need special treatment (as with
                partial clipping), you still can check for this with something
                like:
                ...
                image_ptr:=GetImage(x1,y1,x2,y2,1-PAGE); {1-PAGE=visible page!}
                IF ERROR<>Err_None
                 THEN ... {probably not enough memory}
                 ELSE IF (was_cut) OR (image_ptr=NIL)
                       THEN ... {partial or total clipping occured}
                       ELSE ... {no clipping at all}
               )
             - possible ERROR-values returned are: Err_NotEnoughMemory and
               Err_InvalidPageNumber

Note       : As already mentioned, GetImage() only works on screen regions in
             the _absolute_ coordinate range 0..319, 0..199, but expects
             _virtual_ coordinates!

See also   : PutImage, coordinates


GetModeByte - function
──────────────────────

Function   : Returns the actual display method set for a sprite

Declaration: {$F+} FUNCTION GetModeByte(Sp:WORD):BYTE; {$F-}

Description: "Sp" specifies the spriteLOADnumber of the sprite from which the
             user wants to know the display mode. The function will return one
             of the valid modes Display_NORMAL, Display_FAST or Display_SHADOW.

Note       : - Again, spriteLOADnumbers are used!
             - If the LOADnumber given doesn't exist (because no sprite has
               been loaded with that number), the routine will return
               Display_UNKNOWN instead.

See also   : Display modes, SetModeByte


GetPixel - function
───────────────────

Function   : Reads a pixel's color

Declaration: {$F+} FUNCTION GetPixel(x,y:INTEGER):BYTE; {$F-}

Description: Returns the color value of the specified pixel with the virtual
             coordinates (x,y) on graphic page PAGE. If (x,y) lies offscreen
             (to be precise: the computed absolute coordinates lie offscreen),
             then zero (= black) is returned.

Note       : Be aware that PAGE is the invisible page, not the one you are
             looking at!

See also   : coordinates, PAGE, PageGetPixel, PutPixel


GRAB - utility
──────────────

GRAB allows you to "steal" graphics from other applications and convert them
into sprite files (*.COD) or background images (*.PIC) for use with ANIVGA.
This program is a terminate-and-stay-resident (TSR) utility that has to be run
before starting those applications from which you want to capture graphic
images.
Pressing the hotkey CTRL-ALT-G will popup a frame which you can move and resize
to select the part of the graphic sreen you want to save (if you are not in a
graphic mode, a graphic mode unknown to GRAB or in a "MSDos critical" situation
you'll here a beep instead). Use the "i/j/k/m", arrow and "8/6/2/4" keys for
that task. The space bar will toggle between which corner (the upper left or
lower right one) will be used for resizing the box. Press ESC anytime to escape
from GRAB back to your application.
By default, GRAB starts in sprite capture mode: if you press "s"ave, "w"rite or
just RETURN, GRAB will generate a sprite file (starting with the file name
GRAB_000.COD and counting up for following sprites). To get a background image,
toggle into screen capture mode by pressing "t" (a second "t" will switch back
to sprite capture mode again), select the screen region wanted and press "s",
"w" or RETURN to get that part of the screen in the file GRAB_000.PIC (or what-
ever number is actual then).
Naturally, you can't resize your frame in the screen capture mode: it stays at
its initial size of 320x200 points.

Note that GRAB doesn't save color palettes, but only the actual color values of
all the pixels selected. Because ANIVGA uses the standard palette of graphic
mode $13, it is possible that images captured with GRAB may have different col-
ors when used in MAKES or ANIVGA, whenever the application from which you cap-
tured changed the standard palette!

Note also that there is the same restriction for a sprite's size as in MAKES: a
sprite may be 152x152 points in max.

As a last point, the usage of GRAB is restricted to all the standard graphic
modes known by the VGA-BIOS plus the "tweaked" 256 color mode used by ANIVGA
itself. GRAB uses the BIOS-routines to read and write dots (with the exception
of the tweaked mode of course) which makes it relatively slow (but reliable).
As a consequence, you can capture from 16 color or monochrome graphic modes,
too (although it makes little sense to me capturing 16 or 2 color images for
usage in a 256 color sprite toolkit...)

See also   : MAKES


GraphTextBackground, GraphTextColor, GraphTextOrientation - variables
─────────────────────────────────────────────────────────────────────

Function   : Determine how the OutTextXY()-procedures work

Declaration:  TYPE  FontChar=ARRAY[0..5] OF BYTE;
                    Font=ARRAY[0..255] OF Fontchar;
                    FontOrient=(horizontal,vertical);
              CONST GraphTextOrientation:FontOrient=horizontal;
                    GraphTextColor:BYTE=white;
                    GraphTextBackground:BYTE=white;
                    FontHeight=6;
                    FontWidth=6;

Description: Whenever text is to be written to the graphic screen, ANIVGA
             consults some global variables. GraphTextColor is simply the color
             in which the text should be drawn, GraphTextBackground specifies
             the color for the pixels in between the letters with one special
             value: if GraphTextBackground=GraphTextcolor, then only the pixels
             belonging to the letters will be drawn with all others remaining
             unchanged.
             Finally, GraphTextOrientation tells ANIVGA in which direction the
             text should be written with two values being possible: HORIZONTAL
             (default) for left-to-right text and VERTICAL for top-to-bottom
             style text.

Note       : Default color for the text is "white/white" = "white and don't
             change pixel values between letters".

See also   : OutTextXY, BackgroundOutTextXY


HitDetect - function
────────────────────

Function   : Checks whether two sprites collide or not

Declaration: {$F+} FUNCTION Hitdetect(s1,s2:INTEGER):BOOLEAN; {$F-}

Description: Call this routine with the sprite numbers of the two sprites to be
             checked for collision; the function will return TRUE/FALSE when
             the sprites collide/do not collide, respectively.

Note (!)   : - Collision detection is independent of whether the sprites are
               visible or offscreen: ANIVGA uses the corrdinates of the two
               sprites given (in SpriteX/Y) and internal data to check.
             - For this it is possible to check for collisions _before_ drawing
               an image (with Animate) and thus make necessary sprite updates
               at once!
             - Inactive sprites cannot collide:
               (SpriteN[s1] or SpriteN[s2]=0) -> FALSE
             - A sprite can't collide with itself: (s1=s2 -> FALSE)

See also   : Collision-detection


InitGraph - procedure
─────────────────────

Function   : Initialises the VGA card for the use with ANIVGA

Declaration: {$F+} PROCEDURE InitGraph; {$F-}

Description: ANIVGA uses a special graphic mode, which supports 4 graphic pages
             in the resoultion 320x200 pixels and 256 colors. Because this mode
             is not known by the VGA's BIOS, ANIVGA has to reprogram the VGA.
             You should use this command only once to switch into graphic mode.

Note       : InitGraph automatically switches to the invisible graphic page
             1-PAGE.

See also   : Screen, CloseRoutines


InitRoutines - procedure
────────────────────────

Function   : Resets all necessary internal variables of ANIVGA to initial values

Declaration: {$F+} PROCEDURE InitRoutines {$F-}

Description: At program start, some variables have to be set and a few system
             checks are necessary.
             Among these are:
             - SpriteN[] and SpriteAd[] become cleared (= set to 0)
             - Page (the actual drwaing page) is set to 0
             - PageAdr is set to the segment address of the drawing page PAGE
             - BackgroundMode is set to STATIC, i.e.: non-scrollable background
             - BackGndAdr is set to the segment address of the background image
             - StartVirtualX/Y are set to (0,0), making the normal screen coor-
               dinates identical to the virtual screen coordinates
             - the old graphic/text mode which was active at program start is
               stored for restoring it at the program end
             - the system is checked if a VGA card is present and the global
               variable ERROR is set accordingly
             - CycleTime is set to 0, which says that there should be no time-
               control mechanism for the animation rate
             - if the machine is not at least an AT, the time mechanism is
               switched off completely
             - COLOR is set to 15 (= white)

             The first thing you should do in your programs is to look at the
             ERROR variable: if it was set to something different from Err_None
             (by the implicit, automatical call of InitRoutines) then your pro-
             gram should no proceed further.

Note       : - This routine is called automatically at the very beginning of
               every program which uses ANIVGA. For that, there is normally no
               need to call this routine explicitly.
             - Possible ERROR-values returned are: Err_None and Err_NoVGA
             - Note that this is the _only_ routine that definitely sets the
               variable ERROR, either to Err_None or Err_NoVGA. Because it is
               called at the beginning of every program, it is thus assured
               that your application always has a defined value for ERROR!

See also   : ERROR


Line - procedure
────────────────

Function   : Draw a line between the two points specified

Declaration: {$F+} PROCEDURE Line(x1,y1,x2,y2:INTEGER; pa:BYTE); {$F-}

Description: Calling this routine will draw a line between the two points
             (x1,y1) and (x2,y2) on graphic page "pa" and in the color COLOR.
             The routine uses virtual coordinates and clips the line down to
             its visible part.
             "pa" must be one of the values 0, 1 or BACKGNDPAGE (=2).

Note       : - As with all point-setting procedures of ANIVGA, you have to re-
               member ANIVGA's working scheme: the first thing ANIVGA does when
               Animate becomes executed is to copy the background image to the
               actual drawing page PAGE, erasing everything on that image.
               For this reason, a line drawn on the visible page 1-PAGE will be
               visible exactly one animation cycle.
             - Possible ERROR-values returned are: Err_InvalidPageNumber

See also   : PutPixel, BackGroundLine, coordinates


LoadBackgroundPage - function
─────────────────────────────

Function   : Loads a background image from disk

Declaration: {$F+} PROCEDURE LoadBackgroundpage(name:String) {$F-}

Description: This routine loads a bitmap image stored in file "name" into the
             graphic page used for the background image (BACKGNDPAGE).

Note (!)   : - This routine must be called *after* the graphic mode has been
               initialized (with InitGraph())!
             - You can create such images either with the WritePage()- and
               WriteBackgroundPage()-routines of ANIVGA or the GRAB-Utility.
             - Calling this routine is equivalent to use the routine LoadPage()
               with BACKGNDPAGE as second argument.
             - Possible ERROR-values returned are: Err_FileIO and Err_NoPicture

See also   : Background, LoadPage, FillBackground, GetBackgroundFromPage,
             InitGraph


LoadMAX - constant
──────────────────

Function   : Specifies the maximum number of different sprites

Declaration: CONST LoadMAX=1000;

Description: For each physical sprite, ANIVGA uses an internal pointer to its
             data. There are LoadMAX pointers, thus there may be up to LoadMAX
             different spriteLOADnumbers (= different sprites).

Note       : Don't mix this constant up with NMAX!

See also   : NMAX, SPRITE, SpriteLOADnumbers, Spritenumbers


LoadPage - procedure
────────────────────

Function   : Loads a graphic page from disk

Declaration: {$F+} PROCEDURE LoadPage(name:STRING; pa:BYTE); {$F-}

Description: "name" is the MSDOS-path to the graphic image to load, pa the
             destination page (0,1 or BACKGNDPAGE (=2)).

Note       : - The graphic mode must have been initialized (vià InitGraph)
               already!
             - You can generate disk files of graphic pages with the help of
               the WritePage()-routine or with the GRAB-utility program.
             - Don't use this routine to load an image into the SCROLLPAGE,
               i.e.: in background mode SCROLLING!
             - Possible ERROR-values returned are: Err_InvalidPageNumber,
               Err_FileIO and Err_NoPicture

See also   : GRAB, WritePage, background, InitGraph


LoadSprite - function
─────────────────────

Function   : Loads one (or more) sprites into memory

Declaration: {$F+} FUNCTION LoadSprite(name:String; number:WORD):WORD; {$F-}

Description: "name" is the MSDOS-name of the sprite file to load, which can be
             either a single sprite file (*.COD) or a complete sprite library
             (*.LIB): the function will detect automatically, which format is
             used while loading the data.
             "number" is the spriteLOADnumber, the first loaded sprite will be
             assigned to. If the file contains more than one sprite, they will
             get consecutive LOADnumbers.
             The value returned by the function is the numbers of sprites read
             in (i.e.: 0 means "no sprite read", so you should check ERROR in
             that case).

Note       : - Unlike LoadTile(), LoadSprite() loads data into conventional
               memory. For that, you don't have to be in graphic mode to load
               data from disk!
             - Possible ERROR-values returned are: Err_FileIO, Err_NoSprite,
               Err_NotEnoughMemory and Err_InvalidSpriteNumber

See also   : sprite format, MAKES


LoadTile - function
───────────────────

Function   : Loads one or more tiles from disk

Declaration: {$F+} FUNCTION LoadTile(name:STRING; number:BYTE):WORD; {$F-}

Description: This routine loads the background tile file "name" into the
             graphic memory area reserved for tiles (the SCROLLPAGE).
             The starting number for the first tile of the file is "number",
             if there are more than one tile in the named file, they will be
             loaded too (with increasing numbers).
             The function returns the number of tiles read in.

Note (!)   : - This routine must be called *after* the graphic mode has been
               initialized (with InitGraph)!
               What the function actually does is reading in a sprite and con-
               verting it into an internal tile format: if the sprite read in
               doesn't have the proper size of a tile (16x16 pixels), you nor-
               mally will get an appropriate error (Err_NoTile), with one (use-
               ful) exception: if the sprite can be "cut" into tiles (that is,
               its width and height are multiples of 16 pixels each), then
               LoadTile() will do so with the following numbering scheme: from
               left to right and from top to bottom.
               For example, a sprite with (width,height)=(3*16,2*16) points
               would be numbered as: (assuming that "number" = 0)
               ┌────────┬────────┬────────┐
               │        │        │        │
               │   0    │   1    │   2    │
               │        │        │        │
               ├────────┼────────┼────────┤
               │        │        │        │
               │   3    │   4    │   5    │
               │        │        │        │
               └────────┴────────┴────────┘
               Besides, LOADTILE can load a sprite library, too (they will be
               loaded in the sequence in which they appear in the library).
             - Possible ERROR-values returned are: Err_NotEnoughMemory,
               Err_FileIO, Err_NoTile and Err_InvalidTileNumber

See also   : Background, LOADSPRITE, TILE


MAKES - utility
───────────────

The design of sprites is much to tedious to be carried out manually. For this
reason, there are two utility programs to simplify that task. The first one
is a resident program named "GRAB" to capture graphics from other applications
and convert them into sprites, the second is MAKES, a _simple_ spritemaker
program (don't expect too much).
To use it, you must have a mouse installed (and a VGA card, of course).
(Other than ANIVGA itself, the program uses the "normal" 256-color mode $13, so
 a MCGA-adapter should work also)
There are no parameters or such things, just start it!
In the upper right region of the screen there is the so called "work area", in
which you can paint your sprite pixelwise.
At the bottom of the screen, all possible colors are available. To choose one,
point at the color wanted and press the mouse button, to which you want this
color assigned.
All other options are so simple that there should be no descriptions necessary,
so that I only give some general infos here:
Note that sprites are always stored as the smallest rectangle which surrounds
them and starts at the upper left corner (0,0): if you don't have special
reasons to do otherwise, your sprites should start in the upper left corner.
If for example you realize a sprite consisting of one single point at coordi-
nates (a,b), the smallest surrounding box with (0,0) as upper left corner would
be
   (0,0)      (a,0)      of size (a+1)*(b+1) pixels (=bytes)!!!
     ┌──────────┐
     │          │
     │          │
     │          │
     └──────────▀   <─ this is your 1 point
   (0,b)      (a,b)

To determine what areas belong to your sprite and which don't, the program
assumes color 0 to specify no-sprite-areas and all other colors to be part of
your sprite (roughly spoken).

The best way to design a sprite is to start with a cleared work area and draw
the sprite in the midst of it. If you think you're done, use the direction
boxes to align your sprite with the upper left corner. Then click on the
"boundaries" option ("see transparent?": no) to see the sprite's size and
extension in the x/y-directions. This is useful to find very dark points with
color<>0 set accidentally which would extend the sprite size unnecessarily.
If you are unsure whether you can use display mode "Display_FAST" or not, call
"boundaries" a second time and select "see transparent?" _yes_ this time: if
the blinking white parts "spread" out of the parts you think your sprite should
be made of, then you should use "Display_NORMAL", if all the blinking areas are
inside your sprite, you can use "Display_FAST".

Note: - The maximal size for your sprites developped this way is 152x152 points
        (that is only because of the restricted size of the work area on your
         screen; ANIVGA itself can handle sprites up to 32000 pixels in each
         axis or 64K max. size)
      - For more complex sprites, it is often easier to use a commercial pain-
        ting program, capture the sprite with GRAB and edit the resulting
        sprite with MAKES

See also: sprite format, GRAB, Display modes


MaxTiles - constant
───────────────────

Function   : Holds the maximum number of tiles to build the background image

Declaration: CONST MaxTiles=10000;

Description: In background mode SCROLLING, you may use up to MaxTiles tiles
             to build your graphic image.

Note       : -

See also   : Background


NextSprite - variables
──────────────────────

Function   : Holds the "successors" of sprites for sprite cycles

Declaration: VAR NextSprite: ARRAY [0..LoadMAX] OF WORD

Description: To realize a sprite cycle, you must tell ANIVGA which sprites
             should be drawn one after another. It is this information
             NextSprite holds! For example, let us assume that you wanted to
             make the sprite(loadnumber)s 43, 177 and 111 a sprite cycle, i.e.:
             whenever you set a sprite (to be precise: a SpriteN[]-entry) to
             one of these three numbers, ANIVGA should cycle between the three
             sprite-images in the sequence 43->177->111->43->177->111->...
             You would then set NextSprite[43]:=177; NextSprite[177]:=111 and
             NextSprite[111]:=43  (don't forget this final value!) to do so.

Note (!)   : - Most often, you will have the situation that some sprite(load)-
               numbers with consecutive numbers should make up a cycle. In that
               case it is more convenient to use the SetSpriteCycle()-procedure
               to do the job for you
             - Again, note that the routine deals with spriteLOADnumbers! That
               is intentionally, because a sprite cycle is related to the
               _physical_ existent sprite data, or simply spoken: if you make
               5 pictures to form a flickering torch and you are going to use
               10 torches in your animation then each of them should loop
               through this 5-picture-cycle, shouldn't it?
             - NextSprite[] is initially set "to point to itself", that is:
               NextSprite[i]=i for all possible i's. If you had to break off
               a sprite cycle (though I can't think what this should be good
               for...), you must restore this data, e.g.: if you wanted to
               break the sprite cycle above, you would have to set
               NextSprite[43]:=43; NextSprite[177]:=177; NextSprite[111]:=43;
             - As this is a global variable, ANIVGA can't check whether your
               settings make sense or not; thus, it remains your responsibility
               to use proper values!

See also   :   SetSpriteCycle, Sprite cycles


NMAX - constant
───────────────

Function   : Determines the maximum of sprites to be active at the same time
             (minus 1)

Declaration: CONST NMAX=499

Description: This constant sets the size of the internal tables - and thus the
             valid sprite numbers: the indices of the tables SpriteX, SpriteY
             and SpriteN must lie in the range 0..NMAX.
             To state it otherwise, there may be up to NMAX+1 sprites creeping
             around your screen at the same time...

Note       : Don't confound that constant with LoadMAX

See also   : LoadMAX


OutTextXY - procedure
─────────────────────

Function   : Writes a textstring to the graphic screen

Declaration: {$F+} PROCEDURE OutTextXY(x,y:INTEGER; pa:BYTE; s:STRING); {$F-}

Description: ANIVGA has a built-in font, each character consisting of 6x6
             pixels: very ugly, but hey, we want to make animations, not text!
             To write the string "s" to the graphic screen, you must specify
             the upper left starting corner of the text in (x,y):
                 (x,y) -> ▄──────────┐ , where (x,y) are virtual coordinates!
                          │          │
                          │          │
                          │          │
                          └──────────┘
             The text will be drawn in color GRAPHTEXTCOLOR and with the orien-
             tation GRAPHTEXTORIENTATION ("VERTICAL" or "HORIZONTAL").
             A third global variable, GRAPHTEXTBACKGROUND, specifies the color
             which will be used for the background area "beneath" the text
             letters; if GRAPHTEXTCOLOR=GRAPHTEXTBACKGROUND then the text will
             be drawn like TurboPascal's routine does: only the pixels be-
             longing to the letters will be drawn, all others remain unchanged.
             "pa" specifies the graphic page to be drawn on and must be one of
             the drawing pages (0 or 1) or the BACKGNDPAGE (=2) for background
             mode STATIC.

Note       : - Better fonts could have been developped, but they would all
               depend on special assumptions about the text- and/or background
               color(s).
               This font was intented for short and simple text strings and to
               be as small as possible.
               Nevertheless, using a bigger cell (say: 10x10) and several
               colors (for antialiasing effects) can result in very impressive
               fonts - and work, too...
             - Possible ERROR-values returned are: Err_InvalidPageNumber

See also   : GraphtextColor, GraphtextOrientation, GraphtextBackground,
             BackgroundOutTextXY


PAGE - variable
───────────────

Function   : Holds the number of the actual drawing page

Declaration: VAR PAGE:WORD

Description: ANIVGA uses a page flipping approach. Basically this means that it
             alternates between using page 0 and page 1 for its display.
             Although this mechanism should be transparent for the user, ANIVGA
             provides you with the page number of the actual drawing page in
             "PAGE". Note that this number specifies always the invisible page:
             when PAGE=0, then the actual _displayed_ page is page 1 and vice
             versa (ANIVGA always works on the invisible page!).

Note (!)   : Only _read_ this value, never assign a new value to it!


PAGEADR - variable
──────────────────

Function   : Holds the segment address of the actual drawing page PAGE

Declaration: VAR PAGEADR:WORD

Description: As already mentioned, there are four graphic pages, numbered from
             0 to 3. The start addresses of these four pages are used by ANIVGA
             and normally the user should not need to reference them, but with
             PAGEADR at least the address of the actual (invisble) graphic page
             PAGE is available in PAGEADR.

Note (!)   : Only use this variable to _read_ its value, never change it!
             Although this 16-bit-value represents only the segment part of the
             complete address, it is the whole address: the address is norma-
             lized in such a way that the offset part is always zero.

See also   : PAGE


PageGetPixel - function
───────────────────────

Function   : Returns the color value of the specified point

Declaration: {$F+} FUNCTION PageGetPixel(x,y:INTEGER; pa:BYTE):BYTE; {$F-}

Description: If the point at the virtual coordinates (x,y) and graphic page
             "pa" lies on the screen (i.e.: in the range (0,0)..(319,199) in
             absolute coordinates), this routine will return its color, if it
             is offscreen, the function returns zero.
             "pa" should be one of the values 0, 1 or BACKGNDPAGE (=2).

Note       : - If you want to read a pixels' color from the _visible_ page, you
               have to remember that it is the opposite of the _actual_ page
               (that is, you have to use "1-PAGE" as page number).
             - Although only values of 0,1 and BACKGNDPAGE (=2) make sense as
               "pa" values, the routine doesn't check that (for improved speed)
             - For that, the routine _doesn't_ return Err_InvalidPagenumber or
               something similiar in ERROR!

See also   : Background, Coordinates, GetPixel


PagePutPixel - procedure
────────────────────────

Function   : Plots a point at a specified page

Declaration: {$F+} PROCEDURE PagePutPixel(x,y:INTEGER; color,pa:BYTE); {$F-}

Description: This routine is very similiar to PutPixel(), but it lets you
             specify explicitly on which graphic page the point shall be drawn.
             (x,y) specify the virtual coordinates of the point to be drawn in
             color "color". If this point lies onscreen (i.e.: its absolute
             coordinates are between (0,0)..(319,199)), it will be drawn on the
             specified page "pa", which must have one of the values 0, 1 or
             BACKGNDPAGE (=2). The latter only makes sense if STATIC is used as
             background mode.

Note       : - Don't forget that this routine works with virtual coordinates.
             - Note also that the point is _not_ drawn automatically on the
               background page if pa=0 or pa=1, thus it will be visible exactly
               one animation cycle (and be overdrawn by the background image
               then).
             - Because of ANIVGA's working scheme, you probably want to use
               this routine AFTER calling Animate() (else, your point would be
               overdrawn by the background image immediately) if pa=1-PAGE.
               If you want to draw the point at the _visible_ page, remember
               that it is the "opposite" of the _actual_ drawing page, i.e.:
               you have to use "1-PAGE" for "pa".
             - For improved speed, the routine _doesn't_ check the "pa"
               variable to have a valid value, so there will be no report to
               ERROR (Err_InvalidPageNumber or the like) available!
               It remains your responsibility to assure a proper value for pa!

See also   : BackgroundPutPixel, PutPixel, coordinates, How ANIVGA works


PutImage - procedure
────────────────────

Function   : Pastes a formerly copied image to the screen

Declaration: {$F+} PROCEDURE PutImage(x,y:INTEGER; p:POINTER; pa:WORD); {$F-}

Description: PutImage() is the counterpart of GetImage(): use GetImage() to
             copy part of the screen and PutImage to paste it somewhere. (x,y)
             is the upper left corner of the destination (in _virtual_ coordi-
             nates), "p" is the pointer given by GetImage() and "pa" is the
             number of the graphic page (0, 1 or BACKGNDPAGE (=2)) of the des-
             tination.
             If p equals NIL, the routine does nothing at all; this is useful
             because you can PutImage() directly on the result of a GetImage()
             call without further checking for clippings.

Note       : - Like GetImage(), this routine also works only when the _virtual_
               coordinates translate into _absolute_ coordinates in the range
               of 0..319, 0..199, that is: they must lie on the visible part of
               the screen, everything else is clipped off.
             - Possible ERROR-values returned are: Err_InvaliPageNumber

See also   : GetImage, coordinates


PutPixel - procedure
────────────────────

Function   : Plots a point

Declaration: {$F+} PROCEDURE PutPixel(x,y:INTEGER; color:BYTE); {$F-}

Description: (x,y) specify the virtual coordinates of the point to be drawn in
             color "color". If this point lies onscreen (i.e.: its absolute
             coordinates are between (0,0)..(319,199)), it will be drawn on the
             visible page 1-PAGE.

Note       : This routine is not the same as TurboPascal's one: it works with
             virtual coordinates! Note also that the point is _not_ drawn on
             the background page, thus it will be visible for exactly one ani-
             mation cycle (and be overdrawn by the background image then).
             Because of ANIVGA's working scheme, you probably want to use this
             routine AFTER calling Animate() (your point will then be visible
             until the next call to Animate()).

See also   : BackgroundPutPixel, PagePutPixel, coordinates, How ANIVGA works


PutTile - procedute
───────────────────

Function   : "Pastes" a tile into the background image

Declaration: {$F+} PROCEDURE PutTile(x,y:INTEGER; TileNr:BYTE); {$F-}

Description: After you have defined a background scrolling area, you can use to
             PutTile() to arrange them as wanted to build your background image.
             (x,y) is the virtual coordinate where you want the tile "TileNr"
             to be placed.
             (x,y) will be changed to be a multiple on 16 in each direction
             and must then lie in the range (BackX1,BackY1)..(BackX2,BackY2).

Note       : - Of course, this routine only makes sense when you use background
               mode SCROLLING!
             - (x,y) will be drawn to the upper left to fall on the grid.
             - Possible ERROR-values returned are: Err_InvalidCoordinates

See also   : background, tile, SetBackgroundScrollRange, coordinate, BackX1,
             BackX2, BackY1, BackY2


Screen - procedure
──────────────────

Function   : Chooses the display page.

Declaration: {$F+} PROCEDURE Screen(pa:BYTE) {$F-}

Description: Call Screen() with a value between 0 and 3 which tells the routine
             to which graphic page it should switch. This is done by repro-
             gramming the VGA start address registers. For a flickerfree dis-
             play, this switching is synchronized to the vertical retrace
             signal.

Note (!)   : - You should not use this routine if you are not absolutely sure
               what you are doing! Be aware that ANIVGA relies on the fact that
               the actual drawing page is PAGE and its segment address is in
               PAGEADR while the visible page is 1-PAGE!
             - Although it makes little sense to apply this routine to graphic
               pages other than 0 or 1, it is possible to set "pa" to 2 (=BACK-
               GNDPAGE) or 3 (=SCROLLPAGE).

See also   : PAGE, PAGEADR, InitGraph


ScrollPage - constant
─────────────────────

Function   : Holds the page number of the backround page

Declaration: CONST SCROLLPAGE=3;

Description: When using background mode SCROLLING, BackGndPage specifies the
             page number of the tile buffer used to build up the background
             image for animations.

Note (!)   : Use of this constant only makes sense when using background mode
             SCROLLING!

See also   : BackGndPage, Background


SetBackgroundMode - procedure
─────────────────────────────

Function   : Chooses one of the possible background modes of ANIVGA

Declaration: {$F+} PROCEDURE SetBackgroundMode(mode:BYTE); {$F-}

Description: ANIVGA has two possible ways of handling background you can choose
             of: "STATIC" or "SCROLLING" backgrounds with several advantages
             and disadvantages, each (see background). Specify the mode you
             want to use in the "mode" variable.

Note       : - Default value set by ANIVGA is STATIC.
             - Possible ERROR-values returned are: Err_InvalidMode

See also   : background


SetBackgroundScrollRange - procedure
────────────────────────────────────

Function   : Specifies the scrollable background area in mode SCROLLING

Declaration: {$F+} PROCEDURE SetBackgroundScrollRange(x1,y1,x2,y2:INTEGER) {$F-}

Description: (x1,y1) is the upper left corner of the background scroll area,
             (x2,y2) the lower right corner (all virtual coordinates).
             ANIVGA will round the points given to fit on a grid with mesh 16,
             that is, x1,y1,x2,y2 will be changed to be all multiples of 16.
             These new values will be stored in the (global) variables BackX1,
             BackY1, BackX2, BackY2 for further use.
             Besides that, XTiles and YTiles will hold the width and height of
             the choosen background area in tiles.

Note       : - You can read the Back??-variables for your information, but
               don't change them!
             - Of course, this routine only makes sense when you are going to
               use SCROLLING as background mode.
             - The upper left corner (x1,y1) will be drawn to the upper left,
               the lower right corner (x2,y2) to the lower right to fall on the
               grid.
             - Don't forget that the tile memory is limited; you can't select
               an area bigger than MaxTiles (=10000) tiles, that is more than
               2560000 pixels².
             - Possible ERROR-values returned are: Err_InvalidCoordinates and
               Err_BackgroundToBig

See also   : background, tiles, PutTile


SetCycleTime - procedure
────────────────────────

Function   : Defines the maximum animation speed

Declaration: {$F+} PROCEDURE SetCycleTime(milliseconds:WORD); {$F-}

Description: There are lots of PC-compatible machines with a broad range of
             clock rates, wait states and different speeds of their graphic
             cards. With this routine you can set the time an animation cycle
             has to last at least: at the very end of Animate, the routine
             checks whether at least "milliseconds" milliseconds have been past
             since the last call to this routine and waits if necessary.
             If you give 0 milliseconds as an argument or your machine is not
             (at least) an AT class machine, there will be no such time control
             mechanism and the animation will always take part at the maximal
             speed on the specific machine (this is also the default value).

             For example: "SetCycleTime(100);" would restrict the animation
             rate even on the fastest 80586 machines to at most 1sec/100msec
             = ten frames per second.

Note (!)   : - Because there is no such high precision timer on PC/XT computers
               as required, SetCycleTime() is ignored on these machines.
               Anyway, this should be not to hard because these computers are
               normally that slow that they would not have been slowed down
               either.
             - The accuracy of this timing mechanism is better than 1 milli-
               second.


SetModeByte - procedure
───────────────────────

Function   : Specifies the way a sprite will be displayed

Declaration: {$F+} PROCEDURE SetModeByte(Sp:WORD; M:BYTE); {$F-}

Description: This routine assigns one of the possible display methods "M"
             (Display_NORMAL, Display_FAST, Display_SHADOW) to the specified
             spriteLOADnumber "Sp".

Note       : - Because this kind of information is stored directly inside the
               sprite data, the sprite must have been loaded already for this
               action to work.
             - For the same reason, this routine works on spriteLOADnumbers,
               not sprite numbers (>gee, again!<): a display method set for one
               spriteLOADnumber will affect all sprites with that LOADnumber!
               Most often, that is okay (e.g.: if you use the sprite of a foot-
               ball player ten times, it is quite normal to use the same dis-
               play mode for all ten players!), if you really must use a sprite
               with two different display methods at the same time, you can use
               the following trick: load the sprite's data a second time into
               memory, using a different spriteLOADnumber. For this second
               copy, you can use another display mode.
             - Possible ERROR-values returned are: Err_InvalidSpriteNumber and
               Err_InvalidMode

See also   : SpriteLoadNumber, SpriteNumber, Display methods, GetModeByte


SetShadowTab - procedure
────────────────────────

Function   : Set the amount of shadowing in display mode "Display_SHADOW"

Declaration: {$F+} PROCEDURE SetShadowTab(brightness:BYTE); {$F-}

Description: Whenever a sprite is drawn in "Display_SHADOW" mode, ANIVGA must
             know how much darker these shadow areas should be, compared with
             the brightness of the original (not-shadowed) colors.
             These data is held in the table ShadowTab and is set to 70% of
             the colors original brightness. However, you can use this routine
             to provide more or less darker shadow areas: "brightness" is the
             percentage of the colors original brightness which shall remain,
             e.g.: brightness=0 would mean every shadow is completely black,
             brightness=100 is the original color as shadow (not darkened at
             all), brightness=40 will darken every color by 100-40=60%, etc.

Note (!)   : - This routine takes quite a long time (app. 4s on an 8MHz AT).
             - The argument will be only approximated: the algorithm computes
               the 256 color values needed precisely and matches them as close
               as possible to the 256 default colors of graphic mode $13.
               Note that the palette registers of the VGA card *won't* be
               changed at all! ANIVGA still works with the standard VGA palette
               of the BIOS; what it does is solely creating a color look-up-
               table!
             - Possible ERROR-values returned are: Err_InvalidPercentage

See also   : ShadowTab, Display modes, SetModeByte


SetSpriteCycle - procedure
──────────────────────────

Function   : Links spriteLOADnumbers together to form a sprite cycle

Declaration: {$F+} PROCEDURE SetSpriteCycle(nr,len:WORD); {$F-}

Description: "nr" is the first spriteLOADnumber to be included in the sprite
             cycle and "len" entries (i.e.: from "nr" to "nr+len-1") should be
             tied together.
             The routine will then set the according NextSprite[] entries to
             build this cycle: nr -> nr+1 -> nr+2 -> ... -> nr+len-1 -> nr

Note       : - The routine uses spriteLOADnumbers, _not_ sprite numbers!
             - If you want to link sprite(loadnumber)s which do not have conse-
               cutive (load)numbers, you must do that by setting NextSprite[]
               accordingly.

See also   : Sprite cycles, NextSprite


ShadowTab - "procedure"
───────────────────────

Function   : Table for translating sprite colors into others

Declaration: {$F+} PROCEDURE ShadowTab; {$F-}

Description: If the display mode "Display_SHADOW" is set for a physical sprite,
             its colors will depend not on the values stored in the sprite it-
             self, but on the values found on the screen at the place where the
             sprite shall be drawn: every pixel of the sprite will become dar-
             kened by substituting its corresponding color against the color
             stored in this color table.
             At startup, this table is set to make shadows be approximately 70%
             the brightness of the original colors, but you can adjust this
             with the routine SetShadowTab() if this default is not suitable
             for your application.
             You can even supply a completely different color table (for
             special effects?).
             To do so, define an array "[0..255] of byte" (you can use the pre-
             defined TYPE ColorTable for this), containing for each color of
             the standard palette its substitute (e.g. setting array element
             [8]:=13 would mean: "replace every pixel in the shadow area with
             color 8 against a pixel with color 13") and overwrite the original
             color table by issuing the command "MOVE(my_array,@ShadowTab^,256)"

Note       : - Although this table is declared as a procedure, it really is
               data, not code; so don't call it!
             - There can be only _one_ color table and it is only active in
               display mode "Display_SHADOW".

See also   : SetShadowTab, Display modes, SetModeByte


SPRITE, Spritenumbers, Spriteloadnumbers - information
──────────────────────────────────────────────────────

A sprite is the basic data element used in ANIVGA. Technically spoken, it is
nothing more then a two-dimensional array of bytes which becomes copied to the
screen positions needed, but it is far more comprehensive to think about it as
a photograph of a figure which can be pasted to the screen whereever you want.
To distinguish between different sprites, we use natural numbers, but whenever
we talk about "sprites", we are somehow inaccurate:
You should notice that there are two kinds of "sprite numbers" which should
not be mixed up: one is a spriteLOAD number and represents a handle to the
(physical) sprite data, while the other (normally termed "sprite number") is
a logical number to address the sprite data.
Yet, most often it is clear from the context, which meaning is intended:
For a simple example: if you are going to animate a soccer team, you would
need 11 sprites for the player - but they all have the same shape. This means,
you only have to load one sprite (-> you need 1 spriteLOAD number), but need
11 copies of that to move around the screen (-> you need 11 sprite numbers).
(See section "How ANIVGA works" for more about that)
You can design sprites with the help of the spritemaker-tool MAKES, by using
GRAB to capture and convert graphic screens from other graphic applications
or write your own tools for that (it's really not that difficult you think
now it would be...).

See also   : sprite format, How ANIVGA works


SPRITE CYCLES - information
───────────────────────────

Often, you don't want to have a single picture as sprite, but a sequence of
them which should loop forever. For example, let's assume that you use a torch
as an animation object in your application and you want it to have a flickering
flame.
You would start to draw 5 (say) pictures, which -repeatedly displayed one after
another- would make the impression of your flickering torch. But within your
application, you still want to handle these five different images as one single
object - namely the sprite "torch".
To do so, you can use a capability of ANIVGA, called a "sprite cycle": load the
five images as (physical) sprites and tie their loadnumbers together to form
that sequence!
The easiest way to do that would be to load the images with consecutive numbers
and use the SetSpriteCycle() procedure to form the sprite cycle (see there).
Note that we are talking about linking spriteLOADnumbers here: when you have
built such a cycle for your torch and you want to use 10 torches in your
program, you surely want that each of them behaves the same, that is: they all
should show a flickering flame by using that sprite cycle.
For this reason, ANIVGA uses spriteLOADnumbers, so that every instantiation of
a spriteLOADnumber (i.e.: a SpriteN[]-entry) belonging to a cycle will lead to
a sprite cycle for this sprite!
A small detail at last: if you defined a sprite cycle to be a->b->c->a->...,
and initialized a SpriteN[]-entry to "a", then the first sprite displayed at
the screen will be "b" instead of "a" - why?
Well, ANIVGA handles sprite cycles in the Animate() routine and thus has two
possibilities to update the SpriteN[]-table (by issuing a "SpriteN[] :=
NextSprite[SpriteN[]]" command): _before_ drawing the sprites or _afterwards_.
But when it does _after_ drawing the sprites, the sprites displayed on your
screen (=the old SpriteN[] values before doing the above command) are inconsis-
tent to the according numbers actually held in the SpriteN[]-table!
This could lead to problems (e.g.: when you do a HitDetect() after calling
Animate()). Although this could be circumvented by a special grouping of sub-
routine calls, it is far more convenient to update the SpriteN[]-table _before_
drawing the sprites.
The only drawback with this method is the one stated in the beginning: not the
SpriteN[]-entry supplied by you will be drawn, but its "successor"
NextSprite[SpriteN[]]!
However, most often that won't be that bad and *if* it would, you still could
compensate for it by using the sprite's predecessor (in the above example, you
would use "c", as it is the predecessor of "a", to display "a").


SPRITE FORMAT - information
───────────────────────────

As already said, a sprite is nothing more then a two-dimensional array of bytes
which becomes copied to the screen positions needed.
For quick animations, the data should be stored in a format which causes few
and simple transformation steps when accessing the data, but it is hard to
keep up with that principle, because the graphic mode used is "planed".
This means that points are _not_ stored sequentially into the graphics memory,
but in a rather strange way: every 4 points use the same address, but lie in
different "bitplanes". To cut it short: clipping and drawing sprites is hell
therefore (and surely one reason why there are so less tools for this mode)
and ANIVGA uses a very special format to store a sprite (= *.COD-files):

      0..1   DW offset to Plane_0_Data (points with x-coord. MOD 4=0)
      2..3   DW offset to Plane_1_Data (points with x-coord. MOD 4=1)
      4..5   DW offset to Plane_2_Data (points with x-coord. MOD 4=2)
      6..7   DW offset to Plane_3_Data (points with x-coord. MOD 4=3)
      8..9   DW sprite width (DIV 4), rounded up if not dividable by 4
      10..11 DW sprite height in lines
      12..15 DB 1,2,4,8      ; constants (translate-table)
      16..17 DW SpriteLength ; length of this sprite file
      18..37 DW 10 dup(?)    ; reserved area for future use
      38..39 DB 'K','R'      ; code for "this is a sprite file"
      40     DB 1            ; version
      41     DB 0            ; default display mode (0=Display_NORMAL)
      42..43 DW offset pointer to left boundary table
      44..45 DW offset pointer to right boundary table
      46..47 DW offset pointer to top boundary table
      48..49 DW offset pointer to bottom boundary table
      50..SpriteLength-1: boundary- and plane data tables

(If you should wonder why all pointers are only 16 bit long: the maximal size
 of one sprite is 64k, so offset pointers are sufficient.
 Another trick is that ANIVGA loads sprites at segment boundaries; for that,
 you don't have to distinguish between "relative offsets" and "offset poin-
 ters": if normalized segment addresses (=offset part is ε [0..15]) are used to
 address sprites, the offset part is always 0, so the two terms are identical!)

The Plane_?_Data tables consist of the points of the sprite (1 pixel = 1 byte);
if the sprite width is 12 pixels (say), then each table would hold 12/4=3 bytes
for each of the sprite's rows:
Plane_0_Data = color of pixels 0,4,8 of 1. sprite row
               color of pixels 0,4,8 of 2. sprite row
               ...
Plane_1_Data = ditto, for pixels 1,5,9
Plane_2_Data = ditto, for pixels 2,6,10
Plane_3_Data = ditto, for pixels 3,7,11

The boundary tables hold the outermost positions of the sprite:
 The left/top/right/bottom boundary table holds the leftmost/topmost/rightmost/
 bottomost pixel of each row/column/row/column (or 16000/16000/-16000/-16000 if
 none exists), respectively:
left boundary table = leftmost pixel coordinate of 1. sprite row  (or 16000)
                      leftmost pixel coordinate of 2. sprite row  (or 16000)
                      ...
Note that each entry in the boundary tables consists of a signed integer!

Note also that sprites are always stored as the smallest, the figure including
box (rounded up in the x-direction to the next multiple of 4), but that the
values of the "superfluous points" stored in the plane tables doesn't matter at
all (no difference which display mode is used for the sprite!), because ANIVGA
uses only the bytes of the areas which belong to the _real_ sprite-figure
(ANIVGA determines this parts by assuming the sprite to be "horizontal convex"
and uses the boundary tables to compute them).
(Don't worry if you do not understand these technical details now -- hopefully,
you won't need them at all).

See also   : MAKES, Display modes, convex, sprite library


SPRITE LIBRARY - information
────────────────────────────

Sprite files can be combined to sprite libraries. The main advantage of this is
that you can reduce the number of files needed for your programs dramatically:
A normal program will use approximately 20..40 different sprites, so that you
would have 20..40 files only for your sprites!
But ANIVGA's routine to load sprites "loadSprite()" is flexible enough to dis-
tinguish whether the file to be loaded contains one or more sprites and loads
them all.
To construct such a "sprite library" (suggested filename extension: .LIB), you
just use MSDos' COPY-command with the binary option "/B"; for example:

 COPY /B sprite1.cod+d:\sprites\sprite2.cod+testspr.cod A:\mylib.lib

would concatenate the three sprites "sprite1.cod", "d:\sprites\sprite2.cod" and
"testspr.cod" and build the sprite library "A:\mylib.lib".
You can reverse this process with the UNLIB-utility.

See also   : UNLIB, sprite format, loadSprite


SpriteAd - variable
───────────────────

Function   : Store the pointers to the sprites' data

Declaration: VAR SPRITEAD:ARRAY[0..LoadMAX] OF WORD;

Description: Whenever you load a (physical) sprite with LOADnumber xxx, ANIVGA
             stores the sprite's data somewhere in RAM and maintains a pointer
             which points to the beginning of this data as a handle to access
             the data: this handle is stored in SpriteAd[xxx] and reflects the
             segment part of the starting address of the data.

Note       : Don't change that data directly unless you are absolutel sure what
             you are doing!

See also   : LoadSprite, SPRITE, Sprite Format


SPRITEN, SPRITEX, SPRITEY - tables
──────────────────────────────────

Function   : Hold the values of all sprites to be drawn in the next animation
             cycle.

Declaration: VAR SpriteN:ARRAY[0..NMAX] of Integer  (SpriteX/Y dto.)

Description: ANIVGA is based on tables: in SpriteN[] you must declare, which
             sprites shall be drawn in the next animation step. To do that,
             store the spriteLOAD number of the sprites into the SpriteN[]-
             entries; a zero indicates that the according sprite is inactive
             and should not be displayed.
             For every active sprite (SpriteN[i]<>0), a pair of virtual coor-
             dinates in the range -16000..+16000 must be specified in the
             SpriteX[i] and SpriteY[i] entries to determine the sprites' po-
             sition on the (virtual) screen.
             These coordinates will be transformed internally into real coor-
             dinates to decide whether the sprite is onscreen and has to be
             displayed or not.

Note       : If you have less sprites than are allowed by the system (that is:
             less than NMAX+1), your decision what table entries you use are
             arbitrary; if for example you have only two sprites, it won't
             matter, if you use SpriteN[0] for the first one and SpriteN[1]
             for the other or vice versa, or SpriteN[123] and SpriteN[310] or
             whatever valid indices you can think of - except in one point:
             the sprites are drawn in reverse order, that means SpriteN[NMAX]
             is drawn first, then SpriteN[NMAX-1] ... SpriteN[0].
             For that, if two (or more) sprites overlap each other, the one
             with the smallest index is drawn topmost and covers the other(s).

             For performance reasons you should observe another rule: if you
             use different display methods for different sprites then try to
             group your sprites in such a way, that sprites with the same dis-
             play method have continous indices. As an example: if the sprites
             with (load)number 1 use one method and the ones with number 2
             another, then the sequence SpriteN[]=(...2,2,2,2,2,...,1,1,1...)
             would be better than (...2,2,1,2,...,1,2,...,1,2,...).
             This is due to the fact that whenever ANIVGA has to draw a sprite
             with a display method other than the active one, it must inter-
             nally switch from one method to the other which costs some time.

See also   : SetModeByte


StartVirtualX, StartVirtualY - variables
────────────────────────────────────────

Function   : Specify the upper left corner of the visible world

Declaration: CONST StartVirtualX:INTEGER=0;
                   StartVirtualY:INTEGER=0;

Description: When working with virtual coordinates, your screen displays only a
             very small window (320x200 points) of this "virtual screen"
             (32000x32000 points). To tell ANIVGA which part of this virtual
             screen is to be displayed, you specify the upper left corner of
             the visible part in (StartVirtualX,StartVirtualY).
             For example, setting (StartVirtualX,StartVirtualY) to (100,1000)
             would define that the part of the virtual screen having x-coordi-
             nates ε [100..100+XMAX] and y-coordinates ε [1000..1000+YMAX] to
             be displayed.

Note       : Setting these variables doesn't affect the HitDetect-function: if
             two sprites collide outside the visible area, it will be detected,
             still.

See also   : coordinates


Table - TYPE
────────────

Function   : Supply a data type for the animation variables

Declaration: TYPE Table=ARRAY[0..NMAX] OF INTEGER;

Description: A lot of variables in ANIVGA have to be of type "one entry for
             each sprite" and "Table" is the appropriate form for that.

Note       : -

See also   : SpriteX, SpriteY, SpriteN


Tile - information
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"Tiles" are graphic images, 16 pixels wide and high. They are used to define a
scrollable background image when you use SCROLLING as background mode.
Due to memory limitations, it is impossible to hold a complete background image
in memory (because virtual coordinates range 32000 pixels in x/y-directions,
one would need app. 977 MB (!) RAM for that).
Instead, you may define up to 256 different tiles and then combine them to form
the graphic background, which may consist of up to MaxTiles (=10000) tiles
(using the 256 different tiles).
(A simple example for that can be found by "Background").
ANIVGA stores tiles in a slightly different format then sprites internally, but
you don't have to bother your head about that: on disk, tiles have the same
format as sprites, so you can use all the utility programs to create/edit
sprites also to create/edit tiles! The only restriction you have to care about
is, that a tile has the definite size of 16 pixels in each direction (but see
the LoadTile()-function for some simplifications about even that).

See also   : Background, LoadTile


UNLIB - utility
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Sometimes, you will want to reverse the process of building a sprite library,
that is: you want to split a sprite library into the sprite files of which it
consists.
To do that, call UNLIB with the name of the sprite library to split. UNLIB will
then create the files UNLIB000.COD, UNLIB001.COD, UNLIB002.COD,...  which re-
present the sprite files wanted.
Note here that UNLIB cannot restore the original filenames you used (there is
no such entry in a sprite's header). For that, it is a good idea to write down
the names and sequence of the sprite files used in building a sprite library.
(If you didn't, you still can load every extracted sprite with MAKES, look at
 it and give it the right name then)

See also   : sprite library, MAKES, sprite format


VIRTUAL COORDINATES - information
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See        : coordinates


WriteBackgroundPage - procedure
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Function   : Saves the background image to disk

Declaration: {$F+} PROCEDURE WriteBackgroundPage(name:STRING); {$F-}

Description: This is merely a shortcut of the WritePage()-procedure (see
             there), i.e. WritePage(name; BACKGNDPAGE) would do an equivalent
             job.

Note       : Possible ERROR-values returned are Err_FileIO

See also   : WritePage


WritePage - procedure
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Function   : Saves a graphic page to disk

Declaration: {$F+} PROCEDURE WritePage(name:STRING; pa:BYTE); {$F-}

Description: To save an image of one of the drawing pages (0 or 1) or the back-
             groundpage BACKGNDPAGE (=2), specify the approriate page number in
             "pa" and a valid MSDOS-path/name where to store the data in
             "name".

Note       : - Make sure that your disk has enough space to hold the data: one
               page is stored as 64003 bytes!
             - You can't use this procedure for saving the background page "pa"
               =SCROLLPAGE in background mode SCROLLING!
             - Possible ERROR-values returned are: Err_InvalidPageNumber and
               Err_FileIO

See also   : WriteBackgroundPage, LoadPage


XMAX - constant
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Function   : Specifies the maximal absolute x-coordinate

Declaration: CONST XMAX=319

Description: XMAX is the biggest _absolute_ coordinate in the x-direction which
             can be used: all x-coordinates must lie in the range 0..XMAX.

Note       : Probably, you will never use this constant at all, because nearly
             everything in ANIVGA's user interface works with _virtual_ coordi-
             nates, but who knows...

See also   : YMAX, coordinates


XTiles - variable
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Function   : Holds the width of the scrollable background image in tiles

Declaration: VAR XTiles:INTEGER;

Description: When using background mode SCROLLING, you have to specify the size
         of your scrolling background area (with the SetBackgroundScroll-
         Range()-procedure). ANIVGA adjusts these values slightly and
         computes the size of the resulting background image in tiles.
         The width of this area (in tiles) is then stored in XTiles.

Notes       : Don't change this variable directly!

See also   : YTiles, Background, SetBackgroundScrollRange


YMAX - constant
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Function   : Specifies the maximal absolute y-coordinate

Declaration: CONST YMAX=199

Description: YMAX is the biggest _absolute_ y-coordinate which may be used,
             that is, every y-coordinate must lie in the range 0..YMAX.

Note       : Probably, you will never use this constant at all, because nearly
             everything in ANIVGA's user interface works with _virtual_ coordi-
             nates, but who knows...

See also   : XMAX, coordinates


YTiles - variable
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Function   : Holds the height of the scrollable background image in tiles

Declaration: VAR YTiles:INTEGER;

Description: When using background mode SCROLLING, you have to specify the size
         of your scrolling background area (with the SetBackgroundScroll-
         Range()-procedure). ANIVGA adjusts these values slightly and
         computes the size of the resulting background image in tiles.
         The heigh of this area (in tiles) is then stored in YTiles.

Notes       : Don't change this variable directly!

See also   : XTiles, Background, SetBackgroundScrollRange