This document describes standard ATALAN library for ATARI 8-bit platform. Some parts of this text require good knowledge of ATARI platform.
Application starts at $2000. When it ends, infine loop is performed. If you want to exit to DOS, execute DOS command at the end of application.
Variables are placed in zero page starting from address 128.
Printing strings is done using standard OS routine. When printing into arrays, it is supposed the array is displayed on screen and conversion to ATARI screen codes is performed.
Atari has hardware support for sprites: players and missiles.
There are four players numbered 0 to 3. Player properties are accessed using player(x).property syntax.
Following properties are defined:
x X position of a player ($d000..$d003)
color hardware color (use in DLI or when system VBI is turned off) ($d012..$d015)
scolor system color (704..707)
size width of the sprite ($d008..$d00b)
gfx byte with current player data ($d00d..$d010)
bitmap array with bitmap for the player
There are four missiles numbered 0 to 3.
Missile properties are accessed using missile(x).property syntax.
Every missile has same color as appropriate player (unless specified differently).
You may set the color either by using player(x).color or misile(x).color.
x X position of a player ($d000..$d003)
bitmap all missiles share the same bitmap (2 bits for each missile)
size size of bitmaps ($d00c)
gfx byte with current missiles data
color Missile color.
PMG memory initialization
To use PMG, it is necessary to define PMG memory and set it to appropriate register. It is also necessary to allow DMA for PMG. This is done by setting two registers.
As registers, specifying this are not used only for PMG, they are not part of PMG namespace.
Following piece of code performs necessary initialization.
DMACTL = playfield + dl + players + missiles + hires_sprites
GRACTL = players + missiles
It also defines width of playfield, and use of hires sprites.
Specifying PMG memory address manualy
Atalan will assign memory address to PMG automatically. If you want to specify some specific address in memory, you can do this by declaring address of pmg.memory variable.
Font is 1024 bytes (128 chars, 8 bytes per character) aligned on one-kb boundary Font will be usually defined using const array and file initializer. To use such font use set'font macro.
const myfont:font = file "file.fnt"
If you set the font only at one place (i.e. you are using just one font), you can specify the file directly.
set'font file "file.fnt"
It is possible to write interrupt routines directly in ATALAN. Compiler will create appropriate code to
VBI procedures are executed every frame (1/50s on PAL, 1/60 on NTSC). Defered VBI is used (consult ATARI ROM manual to understand what it means), so hardware registers must be used to change colors etc.
VBI procedure must be of type VBI. It takes no arguments.
To activate the interrupt, use on'vbi procedure.
COLBK = COLOR0(5) ;as we are using deferred VBI, we must copy the color to hardware register
Atalan supports Raster Music Tracker modules for playing music in module rmt.
;We must inform compiler that we are going to use Raster Music Tracker (rmt).
;Declare the module to use.
const musmod:array = file "delta.rmt"
;Initialize the music engine (specify, which module to use)
;It is necessary to call the music'play routine every 1/50 of second.
;We will call it from VBI, here we prepare the appropriate routine.
;It is of course possible to add other functionality to VBI, if necessary.
;Start playing (set the vbi to our routine).
;We cannot set the music'play routine directly to VBI, because it is normal
;subroutine, not interrupt routine.
music'init(module:adr track:byte = 0)
adr specifies byte array containing the module, track is optional argument specifying which track of the module to start playing (for example when module contains multiple songs).
Wait for the end of current scan-line. (Performs sta WSYNC).