F1 Licenseware/F1 Licenseware - Volume 1.iso/disks/050a.dms/050a.adf/TEXTS/chapter10.txt

Text File | 1992-02-26 | 19KB | 471 lines

                    The Absolute Beginners Guide To Amos
                    -------------------------------------
                                 Chapter Ten
                                 -----------

We are now going to take a good look at Bobs.

Bob is short for Blitter Object, don`t confuse Bobs with sprites, my advice,
at this stage at least, is to forget about Sprites. They are a bit harder to
use, but they will have their uses as you may find in the future.

A Bob is a moveable object. It could be an Alien in Space Invaders game or
the Pacman character from the game of the same name. A bob can be anything
you want it to be.

To start with we will have to either create our own bobs in an art package
like Dpaint or use some existing ones already on disk.  Luckily on this very
disk in the BOBS drawer we have a bob file called SPACECRAFT.ABK. The ABK by
the way stands for Amos BanK.

If you want to create your own bobs, then as I mentioned you will have to
draw them in an art program, save out the IFF picture, load the IFF picture
into the Amos Sprite Grabber program, cut them out and save them as
an ABK file.  You can then load the ABK file into bank 1 of your program.
It`s not as complicated as I have just made it sound really.

Our first mission then is to load our bobs into a memory bank.  Bank one is
especially reserved as a sprite or bob bank.  By the way you can load other
files into bank 1 if you do not need bobs or sprites in your program.

LOAD "DF0:BOBS/SPACECRAFT.ABK"
--------------------------
This will load the ABK file into bank one.  How does Amos know which bank to
load it in, You may ask?  Amos examines the file and sees it is a sprite or
bob bank file and so loads it into the default bank which as I mentioned
earlier is bank one. You can of course put

LOAD "DF0:BOBS/SPACECRAFT.ABK",1

If that is your preference.

So, we have our bobs loaded into bank one, the next step is to ready the
screen for printing our bob onto:

FLASH OFF: CURS OFF: HIDE: PAPER 0: CLS 0
-----------------------------------------
If we didn`t turn FLASH OFF (remember colour number three?) Then any part of
our bob that appeared in colour three may flash, we do not need the text
cursor or the mouse for this particular program so we disable these, set the
paper colour to 0 (usually black, depending on the palette) and CLear the
Screen to colour zero (black) as well. You don't have to do any of the above
but it makes sense to turn the FLASHing off. It looks neater with no cursor
winking away in the top left hand edge of the screen and the mouse would just
be in the way, doing nothing. You can of course CLear the Screen in any
colour you wish.


GET SPRITE PALETTE
-------------------
NOTE: In Amos pro you can use GET BOB PALETTE but in the original Amos
      it is still called SPRITE, don`t let this confuse you, as they are the
      same.

This takes the colours used by the bobs in bank one and replaces Amos`s
default screen colours. The simplest way to understand this is to put a REM
or a ` in front of the GET SPRITE PALETTE command, this will stop Amos
executing that line and you will see the effect. A load of garbled colours.
This is because Amos is displaying the bob in the default colours and not the
colours that the bobs were originally drawn in.  Remember this technique of
putting REMs or ` in front of lines, it`s a useful way of debugging programs
without actually deleting lines. Useful things those REMs.


BOB 1,10,100,1
--------------
Blimey! that looks complicated, yes, it looks it but it`s fairly straight
forward really. Please make a note of the following because I doubt very
much if you will remember this first time.  I will now break down each part
of the line:

BOB 1
This tells Amos that we wish to use a bob, the 1 is really for our
reference because we can have up to 64 bobs on screen at once and we have to
have a number to refer to each one individually.
It is possible to have more than 64 bobs on screen with some twiddling but a
maximum of 64 is enough for now don`t you think?.

10,100
Remember the LOCATE instruction? This is virtually the same except
now we are using pixels instead of bytes as coordinates, there are eight
pixels to a byte so the range is eight times the width and length of text
coordinates. Don`t harp about it at this stage, it`s not that vital to
understand as with a bit of experimenting you will soon get used to the idea.
So the above line means place the bob at 10 pixels across the screen and 100
pixels down the screen. To recap so far we have,

BOB 1, Tell Amos what bob number we are calling this
BOB 1,10,100 Place our bob 1 at 10 across and 100 down on the current screen.

The last number ,1, is the actual bob image from the bob bank that we want
displayed on the screen.  Experiment by changing the last number to see what
different bobs we have stored in the bank.  A better way of viewing bobs is
to load the Sprite_editor from your Amos disk and press L to load a bob bank
and view/edit them from there.

CLEAR KEY: WAIT KEY
------------------
CLEAR the KEYboard buffer and wait for a key press.

LISTBANK
--------
Just there to show you what is in the bank.


That wasn`t so bad after all. The only confusion may arise from the actual
BOB command itself so I will give you a few examples to make things a little
clearer:

BOB 1,0,0,1        Place BOB at 0 across 0 down image 1 (top left of screen)

BOB 2,10,10,1      Place another copy of image 1 at 10,10

BOB 1,10,100,1     Place our bob 1 (the one at top left of screen) at 10,100
                   Amos will automatically erase the old bob 1 at 0,0 for you

BOB 2,200,100,2    Place bob 2 (which was at 10,10) to 200,100 but also
                   change its image to the bob in slot 2 of the bank.
                   Amos erases the bob at 10,10.


I hope that answers a few questions for you.  Here is the complete listing.


REM EXAMPLE10.Amos
FLASH OFF: CURS OFF: PAPER 0: HIDE: CLS 0
LOAD "DF0:BOBS/SPACECRAFT.ABK"
GET SPRITE PALETTE
BOB 1,10,100,1
CLEAR KEY: WAIT KEY
LISTBANK


Please spend a while playing around with EXAMPLE10.Amos as you will learn an
awful lot about bobs, and keep taking down those valuable notes.


Now placing a bob on screen is fine first time but hardly earth shattering
is it? So to pep things up how about animating the spacecraft a little?
Hmm spacecraft don`t move about a lot in flight except in one direction I
suppose? That blue flame from the engine could be made to look better if
it was animated, let`s do that then. As it happens, in the bob bank, images
one to four are exact copies of the ship with the blue flame just slightly
altered. Now if we were to place image two on top of image one quickly
then image three over image two etc. It would appear the flame was moving.
Remember those flicker books years ago? Something like that.
You will probably suspect this is going to entail a major coding
session and if we were using almost any other language it would, but with
good old Amos things are a lot easier.  We will take the listing from
EXAMPLE10.Amos and add just three lines to achieve our objective, this is the
program in full.


REM EXAMPLE10_1.Amos
FLASH OFF: CURS OFF: PAPER0: HIDE: CLS 0
LOAD "DF0:BOBS/SPACECRAFT.ABK"
GET SPRITE PALETTE
CHANNEL 1 to BOB 1
BOB 1,10,100,1
ANIM 1,"(1,5)(2,5)(3,5)(4,5)L"
ANIM ON
CLEAR KEY: WAIT KEY
LISTBANK


Here follows a breakdown of the three new lines,

CHANNEL 1 TO BOB 1
------------------
This weird looking monster is necessary to tell Amos we are about to do some
ANIMating, you don`t need to understand how it works at the moment but you
need to understand that it is needed to use ANIMations, as this is the first
time in this program that we are to use a CHANNEL we may as well use CHANNEL
1, and the starting bob we are about to use is bob 1 so we use CHANNEL 1 to
BOB 1.  This command tells Amos to set up an interrupt channel. As you have
probably never heard of interrupts, I will explain briefly.  An Interrupt is
like having two programs running at once, your normal Amos program and let us
say an ANIMation, we set the ANIMation to be interrupt driven (that is what
CHANNEL does) and this means every 50th of a second Amos will execute the
ANIMation as well as executing your Amos program.  The beauty of interrupts
are once you have set them up you can forget all about them and they will
keep on running unless you tell them to stop.  To prove this, RUN
EXAMPLE10_1.Amos and press a key to stop the program running, now press
escape and you will see the ANIMation still running under interrupt in the
background. When you stop the program with your key press you were actually
stopping one of two programs being run by Amos the one still running, the
ANIMation has not been told to stop, so obviously it just keeps on running
in the background until told to do otherwise. See later on how to stop this
poor blighter.


ANIM 1,"(1,5)(2,5)(3.5)(4,5)L"
------------------------------
The ANIMation line itself looks very complicated at first so as usual I will
break it down for you:

ANIM 1
Tell Amos there is going to be an ANIMation string. As it`s our first ANIM
string we will name it 1.

(1,5)
Display bob image number 1 and hold it on screen for 5/50ths of a second.

(2,5)
Display bob 2 and hold for 5/50ths

(3,5)
bob 3, 5/50ths

(4,5)
And lastly display bob 4 for 5/50ths of a second

L
The L is short for Loop and this means once Amos has finished displaying
image 4 for 5/50ths of a second it will start all over again from image 1.

Don`t forget you must have all the quotes, commas and brackets exactly as in
the example or you will probably get an error.


ANIM ON
-------
Nothing will actually happen visually until this instruction has been
executed it simply sets the ANIMation on it`s way. If we have more than one
ANIMation in the same program ANIM ON would set ALL the ANIMations in
motion. So if you didn`t want that you would call each ANIMation string by
it`s number i.e. ANIM ON 1. To turn off an ANIMation we use ANIM OFF or
ANIM OFF N.  (N being your Anim number)

Now I will show you the easiest way to make an ANIMated bob MOVE about the
screen.  The following program will use a space picture as a background
screen, place a bob just outside the edge of the screen and then MOVE the bob
across the screen. The bob will then stop and be blown up with an ANIMated
explosion and sound effect. The listing is identical in places to
EXAMPLE10_1.Amos.

REM A small space animation

FLASH OFF: CURS OFF: PAPER 0: HIDE: CLS 0
LOAD "DF0:BOB/SPACECRAFT.ABK"
LOAD IFF "DF0:PICS/SPACE.IFF",0
CHANNEL 1 TO BOB 1
CHANNEL 2 TO BOB 1
DOUBLE BUFFER
BOB 1,-48,20,1
ANIM 1,"(1,5)(2,5)(3,5)(4,5)L"
ANIM 2,"(17,5)(18,5)(19,5)(20,5)(21,5)(22,5)(23,5)(24,5)(25,5)"
ANIM ON 1
MOVE X 1,"(1,1,370)"
MOVE ON
WAIT 300
MOVE OFF
ANIM OFF 1
ANIM ON 2
BOOM
WAIT 25
ANIM OFF:BOB OFF
CLEAR KEY: WAIT KEY

Looks a right old mess doesn`t it? It is not as complicated as it looks,
trust me.  I am going to do the breakdown as usual so here we go.

FLASH OFF: CURS OFF: PAPER 0: HIDE: CLS 0
-----------------------------------------
I shouldn`t need to explain this.

LOAD "DF0:BOBS/SPACECRAFT.ABK"
--------------------------
Load the bobs.

LOAD IFF "DF0:PICS/SPACE.IFF",0
--------------------------
Load an IFF picture into the current screen, this will be our background
picture.  Apologies for my artwork, I am not an artist.  We covered loading
pictures in a previous chapter so look it up or check your notes if need be.

CHANNEL 1 TO BOB 1
------------------
I fully explained this line in the last listing.

CHANNEL 2 TO BOB 1
------------------
We are assigning another interrupt channel for the explosion, as the
explosion will overwrite bob 1 we will also use Bob 1 for the explosion,
remember not to get the bob number and image number confused.

DOUBLE BUFFER
-------------
To be honest I didn`t actually need to use this command because we are only
using one bob at a time, but DOUBLE BUFFER, in a nutshell, stops your bobs
from flickering.  I won`t go into the technical side of how it works as that
is irrelevant for now and will probably lead to confusion. You should be
aware though that DOUBLE BUFFER uses up around 32K of extra memory,
dependent on the size and amount of colours of the screen you are using.
All you really need to know at this stage is, if your bobs are  flickering
then use DOUBLE BUFFER.

BOB 1,-48,20,1
--------------
Places bob 1 (The ship) at coordinates -48 pixels across and 20 pixels down
the screen.  I shall explain the minus coordinate, -48 is 48 pixels off of
the screen edge so we are placing the ship 48 pixels before the left edge of
the screen which means it is not visible.  I did this so when we start moving
the ship it will appear smoothly from off the screen, a much better effect
than the ship just appearing from nowhere.

ANIM 1,"(1,5)(2,5)(3,5)(4,5)L"
-------------------------------
We covered this exact line in the above example.

ANIM 2,"(17,5)(18,5)(19,5)(20,5)(21,5)(22,5)(23,5)(24,5)(25,5)"
--------------------------------------------------------------
This is the explosion animation string.  It works the same as the ANIM 1
line except it uses more and different images.  The explosion animation
starts with image 17 and ends at image 25 the delay between each frame is
5/50ths of a second.  You could change the delay to a higher number for a
faster animation or a lower number for a slower animation.

ANIM ON 1
---------
This sets the ships engine flame animation into motion.  This time we have
had to tell Amos what ANIM to use (1) because there is more than one ANIM
string set up.  See the ANIM ON line in the last example.

MOVE X 1,"(1,1,370)"
--------------------
This is the instruction that brings the whole scene to life.
I will break this one down further so we can dissect it thoroughly.

MOVE X 1,
---------
This part tells Amos we wish to move a bob horizontally, the 1 is the
bob number we wish to use.

"(1,1,370)"
----------
This is the mechanics of the MOVE instruction, the first number (1) is the
speed of the movement in 50ths of a second, 1 is the fastest possible.
The second (1) is the step count which I have set at one pixel for smooth
movement and the 370 is the amount of pixels we want the ship to move across
the screen and that is it really.  Please take notes on this as to look at it
without knowing what the numbers represent can lead to confusion.
Remember (Speed,pixels,distance) or as the manual puts it (Speed,Step,Count)
whatever suits you.

Note: Although I have set the speed of the ships movement to maximum it
moves across the screen quite slow, this is because I set the step rate at
one pixel for smoothness.  If you want an idea of how fast Amos bobs can be
change the step rate to 4 8 or 16 etc. And you will be amazed.

MOVE ON
-------
The previous move instruction just sets up the information for Amos, this is
the instruction that sets it all in motion.  The ship will not MOVE until
Amos gets to this line (Remember the same thing with ANIM?) Our spacecraft
will now start to move across the screen.


WAIT 300
--------
We know what this does, it tells Amos to wait here and do nothing (apart
from interrupts of course) For six seconds.  The reason I have put this WAIT
here is that the next instructions are for the explosion and I want the
explosion to occur at the other side of the screen, if we didn`t put this
line in the ship would explode almost immediately, try it and see.

MOVE OFF
--------
We are now preparing for the explosion. The first thing we want to do is stop
the ship in it`s tracks. This we achieve with MOVE OFF which turns off all
previously set up MOVE strings.  If we had more than one MOVE command in the
program we would use MOVE OFF N if we only wanted one of the MOVE strings to
be halted.

ANIM OFF 1
----------
Turn off the engine flame animation.

ANIM ON 2
---------
Start the explosion, ANIM 2.

BOOM
----
While the explosion is in progress play the BOOM sound effect.

WAIT 25
-------
WAIT for the explosion to finish.

ANIM OFF: BOB OFF
----------------
Switch all ANIMations OFF and clear the bob from the screen.

CLEAR KEY: WAIT KEY
-------------------
Look it up.


NOTE: This is the simplest way I could find of doing this short Animation
      but there are much better (more complicated) ways.
-------------------------------------------------------------------------

I am afraid that is just the tip of the iceberg as far as bobs, movement
and animation are concerned. It isn`t this tutorials intention to cover
everything but I hope to get you off to a good start and understand the
basics of it.  Here are a few more commands that you will need to know about
if you delve further into bobs.


MOVE y
--------
This works identically to MOVE X, the difference of course is MOVE Y moves
the bob vertically along the screen. A minus value would move up the screen
and a positive value down the screen.


WAIT VBL
--------
This causes Amos to WAIT for a Vertical BLank.  It basically WAITs for Amos
to update the screen which normally happens every 50th of a second,
if you have a problem with a bob not appearing try a WAIT VBL instruction
before or after the BOB command.


MOVE FREEZE N
-------------
Temporarily stop bobs in their tracks, use MOVE ON N to restart.
N is optional.


ANIM FREEZE N
-------------
As above but affects ANIM.


ABOUT AMAL
----------
You may or may not of heard of AMAL, which is a sub-language used in Amos.
We have been using Amal commands for the BOB, MOVE and ANIM commands.
AMAL stands for Animation language and as I said before is interrupt driven.
To cover Amal properly would require another book and I have my reservations
about using Amal, as a lot of other coders do. It is pretty tricky to get to
grips with in places. At first Amal appears to give a huge increase in speed
but once you compile your program that extra speed is lost. So take my
advice and only use Amal when necessary.

Well that`s quite a lot to take in, make those notes and mess with
EXAMPLE10.Amos, EXAMPLE10_1.AMOS and EXAMPLE10_2.Amos
and have some fun trying to make your own animations.


NOTE: The bob file SPACECRAFT.ABK was borrowed from the Amos Extras disk and
      is located in the AMOS SPRITE_600 folder on that disk along with lots
      of other useful bobs.
      The Tracker mod is P.D (author unknown).
      The background picture I managed myself, sorry.


                             End of chapter ten
                             ^^^^^^^^^^^^^^^^^^