HPAVC/HPAVC CD-ROM.iso/OTHIRES.ZIP/hires.doc

Text File | 1996-03-21 | 10KB | 195 lines

                      - THE OUTLAW TRIAD DEMO-SERIES -

────────────────────────────────■ PART IV ■───────────────────────────────────

                           Written by : Vulture/OT
                           Code in    : Assembler
                           Topic      : High resolution

──────────────────────────────■ Introduction ■────────────────────────────────

 Welcome to the Outlaw Triad demo-series! In these series we will be talking
 about programming demo-effects in either pascal or assembler. Theory behind
 the effects shall be discussed while a full sourcecode is also provided.
 In this fourth release we will discuss the basics of high resolution modes
 like 640*480*16. We will make simple stringwriter for use in these modes.
 A full sourcecode in assember is included. It's a part of the sourcecode of
 a BBS intro coded for Magicware. The Outlaw Triad Italian HQ. Enjoy!

─────────────────────────────────■ Theory ■───────────────────────────────────

 Ok, I will not waste much time explaining how a stringwriter works since
 these routines are fairly easy to make. However, I will spend a few bytes
 on it. I mean, this still is a trainer, right? ;-)

 To show some text on the screen, you will have to state the text you
 want. What we want is a label representing the text to show. Like this:

 Label Text Byte
      DB   '   the text you want to show   ',0

 The major advantage of doing it this way is the fact that you can change
 the text very easily. Another way I've seen in some intro sourcecodes is
 stating the numeric values of the text, or something like that. A rather
 odd way of doing things, IMHO.
 Anyway, the "0" at the end of the string means that the text has come to
 an end there. We will take care of that in our stringwriter routine.
 Ok, now how to we show this text? That's the main question here. First, we
 need a font to work with. In most small intros, the fontdata is organised
 in a lineair way. For example, you could scan a pcxfile from left to right,
 top to bottom and save the bytes to a constant. Ok, you also need to know
 the x,y size of the font. We need them for calculating the exact starting
 position in the fontdata of the specific character we want to draw. Next
 thing you need is the character order. An example:

 Label Order Byte
      DB   'abcdefghijklmnopqrstuvwxyz!?.,()":+-'

 Let's take a look at an example of how to locate a character in the data.
 I assume the data is organised in a lineair way like a stated above. Also,
 let's say the x and y size are both 16. If we wanted to locate the letter
 'g', we would add (6*16) to the offset (start) of the fontdata. Why? Take
 a look: The letter 'g' is the seventh letter in the fontorder. We want to
 locate the upperleft corner (!) of that letter. So, by adding (6*16) to the
 offset we are exactly where we want to be! We have simply skipped the first
 6 characters (that is, the first scanline of those characters). Ok, when we
 have located that particular position, we can draw the char. You could do
 something like this:

    - Go into a loop where you:
      - Draw 16 pixels
      - Update pointer to fontdata (remember: fontdata is lineair)
      - Update vga position

 Do this 16 times (y was 16 here) and you're done. Ok, I don't want to waste
 much more space explaining this so here are the steps you could take to show
 some text:                                                ~~~~~

     1 - Load a character from the text
     2 - Do appropiate action (in case of "0")
     3 - Reset counter
     4 - Go into a loop:
       a - Load a character from order
       b - Compare with the character from the text
       c - If not the same, increase counter, back to A
     5 - They were the same, now use the counter to find
         the position of the character in the fontdata
         (The way this is done depends on how the data is
          organised. Check out the source to see what I mean)
     6 - Draw the character
     7 - Do next one

 Well, and that's it! You can use these steps in any resolution you want.
 In our case, high resolution 640*480*16. Let's take a closer look at this
 particular mode, shall we?

 Each byte in high resolution vgamemory represents 8 neighboring horizontal
 pixels! In a byte are 8 bits, so each bit is 1 pixel on the screen! Quite
 a difference compared to standard mode 13h where 1 byte represented one
 pixel on the screen. Ok, since you are working with groups of 8 horizontal
 pixels at a time, the logical screenwidth is now 80. Think about it! The
 screenwidth in pixels is 640. Because 1 byte represents 8 horizontal pixels,
 the logical screenwidth is 640/8=80. You use the logical screenwidth when
 drawing a character on the screen.
 When you write a byte to the screen, you can select the bits (pixels) you
 want by writing the byte into the Bit Mask Register. This is index 08h of
 the Graphic Controller. All enabled bits in this register will be written
 to the screen and all not-enabled bits will not be written to the screen!
 So, with this register you could write a PutPixel routine. Anyway, typical
 code to write a byte (a pattern of 8 horizontal pixels) to the screen can
 look something like:

     mov   dx,03ceh       ; Graphic Controller
     mov   ah,ds:[si]     ; The byte to write (pointed to by ds:si)
     mov   al,08h         ; Bit Mask Register
     out   dx,ax
     movsb                ; From data to vga (es:di points to vga)

 This is exactly what I did in the sourcecode. Note when using the Bit Mask
 Register, all pixels you write to the vga will have the same color. If you
 want them to have different colors you could use a PutPixel procedure in
 which you set the color for the dot to write. Ok, you would like to have
 a PutPixel routine for use in this mode, right? Well, I could give you one
 but I won't. Instead, I will give you some hints on how to code your own.

     - Set color of dot
     - Multiply Y with 80
     - Divide X with 8
     - Y=Y+X
     - Set correct bit (using Bit Mask register => X and 7)
     - Read dummy byte from vga (loading latches)
     - Write byte to screen

 There you go! It shouldn't be hard to write a PutPixel routine now. If you
 don't succeed, please mail me. I will give you my own routine instead.

 Ok, one more thing to discuss and that is setting the color for a dot. Like
 I stated before, you should load the byte you want to write to the screen
 into the Bit Mask Register before you write it to the screen. All enabled
 bits will be written to the screen with the same data as presented in the
 Set/Reset Register! With this, we can set the color of the dot we want to
 write to the screen. The Set/Reset Register is 4 bits width so this leaves
 us with a maximum number of 16 colors. Colorsetting code in assembler:

     mov     dx,3ceh           ; Graphic Controller address register port
     mov     ax,0f01h          ; Index 01h  (enable set/reset register)
     out     dx,ax             ; Enable all 4 bits to be altered
     xor     al,al             ; Index 00h  (set/reset register)
     mov     ah,cl             ; Color (0 to 15)
     out     dx,ax             ; Set color

 There are 2 registers to be altered here. The Enable Set/Reset Register and
 the Set/Reset Register. They are both 4 bits in width. If you enable a bit
 in the Enable Set/Reset Register, the corresponding bit in the Set/Reset
 Register can be altered. And, when you disable a bit in the Enable Set/Reset
 Register, the corresponding bit in the Set/Reset Register can't be altered.
 So, we set all (4) bits in the Enable Set/Reset Register to 1. This way, all
 bits (4) of the Set/Reset Register may be altered. Then, we load the color
 into the Set/Reset Register. Any byte (bits) that is written to the screen
 will have this color. Why don't you make a sample program to test this code?
 It should work just fine. (note: I used this code in my own PutPixel proc).

 One advantage of these high resolution modes is that you need just a few
 bytes to represent an entire character. Like in this example source, you
 only need 2*18=36 bytes. If you want to show a character this size in plain
 mode 13h, you would need 16*18=288 bytes. Quite a difference, eh?
 (note: this doesn't have to be true. When using a single color font, you
 can also store the pixels in bits in mode 13h).
 A disadvantage of high resolution mode is that you only have 16 colors to
 you disposal.

 Now go and take a look at the sourcecode provided in this package. It is
 fully documented so there shouldn't be any problems. If you have troubles
 after all, e-mail me. I like to hear from you!

 Ok, this is all for now. Happy coding!

       - Vulture / Outlaw Triad -

───────────────────────────────■ Distro Sites ■───────────────────────────────

 Call our distros to get all our releases.

  BlueNose    World HQ          [phone]
  FireHouse   Distrosite        [phone]
  The Force   Distrosite        [phone]    More distros wanted!
  MagicWare   Italian HQ        [phone]
  ShockWave   South African HQ  [phone]

──────────────────────────────────■ Contact ■─────────────────────────────────

 Want to contact Outlaw Triad for some reason? You can reach us at our
 distrosites in Holland. Or if you have e-mail access, mail us:

   Vulture  (coder/pr)     [e-mail]

 Our internet homepage:

   http://www.tem.nhl.nl/~comma400/vulture.html

 These internet adresses should be valid at least till june 1996.

──────────────────────────────────────────────────────────────────────────────

                  Quote:  Does killing time hurt eternity?