170 lines
3.9 KiB
Plaintext
170 lines
3.9 KiB
Plaintext
processor 6502
|
|
include "vcs.h"
|
|
include "macro.h"
|
|
|
|
org $f000
|
|
|
|
; Besides the two 8x1 sprites ("players") the TIA has
|
|
; two "missiles" and one "ball", which are just variable-length
|
|
; dots or dashes. They have similar positioning and display
|
|
; requirements, so we're going to make a subroutine that can
|
|
; set the horizontal position of any of them.
|
|
; But we can also use the HMPx/HMOVE registers directly to move the
|
|
; objects by small offsets without using this routine every time.
|
|
|
|
counter equ $81
|
|
|
|
; Initialize and set initial offsets of objects.
|
|
start CLEAN_START
|
|
lda #10
|
|
ldx #0
|
|
jsr SetHorizPos ; set player 0 horiz. pos
|
|
inx
|
|
lda #130
|
|
jsr SetHorizPos ; set player 1 horiz. pos
|
|
inx
|
|
lda #40
|
|
jsr SetHorizPos ; set missile 0 horiz. pos
|
|
lda #$10
|
|
sta NUSIZ0 ; make missile 0 2x-wide
|
|
inx
|
|
lda #70
|
|
jsr SetHorizPos ; set missile 1 horiz. pos
|
|
lda #$20
|
|
sta NUSIZ1 ; make missile 1 4x-wide
|
|
inx
|
|
lda #100
|
|
jsr SetHorizPos ; set ball horiz. pos
|
|
lda #$30
|
|
sta CTRLPF ; set ball 8x-wide
|
|
sta WSYNC
|
|
sta HMOVE
|
|
; We've technically generated an invalid frame because
|
|
; these operations have generated superfluous WSYNCs.
|
|
; But it's just at the beginning of our program, so whatever.
|
|
|
|
; Next frame loop
|
|
nextframe
|
|
VERTICAL_SYNC
|
|
|
|
; 37 lines of VBLANK
|
|
ldx #37
|
|
lvblank sta WSYNC
|
|
dex
|
|
bne lvblank
|
|
|
|
; Draw 192 scanlines
|
|
; We're going to draw both players, both missiles, and the ball
|
|
; straight down the screen. We can draw various kinds of vertical
|
|
; lines this way.
|
|
ldx #192
|
|
stx COLUBK ; set the background color
|
|
lda #0 ; A changes every scanline
|
|
ldy #0 ; Y is sprite data index
|
|
lvscan
|
|
sta WSYNC ; wait for next scanline
|
|
lda NUMBERS,y
|
|
sta GRP0 ; set sprite 0 pixels
|
|
sta GRP1 ; set sprite 1 pixels
|
|
tya ; we'll use the Y position, only the 2nd bit matters
|
|
sta ENAM0 ; enable/disable missile 0
|
|
sta ENAM1 ; enable/disable missile 1
|
|
sta ENABL ; enable/disable ball
|
|
iny
|
|
cpy #60
|
|
bne wrap1 ; wrap Y at 60 to 0
|
|
ldy #0
|
|
wrap1
|
|
dex
|
|
bne lvscan ; repeat next scanline until finished
|
|
|
|
; Clear all colors to black before overscan
|
|
stx COLUBK
|
|
stx COLUP0
|
|
stx COLUP1
|
|
stx COLUPF
|
|
; 30 lines of overscan
|
|
ldx #25
|
|
lvover sta WSYNC
|
|
dex
|
|
bne lvover
|
|
|
|
; Move all the objects by a different offset using HMP/HMOVE registers
|
|
; We'll hard-code the offsets in a table for now
|
|
ldx #0
|
|
hmoveloop
|
|
lda MOVEMENT,x
|
|
sta HMCLR
|
|
sta HMP0,x
|
|
sta WSYNC
|
|
sta HMOVE
|
|
inx
|
|
cpx #5
|
|
bcc hmoveloop
|
|
; This loop also gave us 5 extra scanlines = 30 total
|
|
|
|
; Cycle the sprite colors for the next frame
|
|
inc counter
|
|
lda counter
|
|
sta COLUP0
|
|
clc
|
|
ror
|
|
sta COLUP1
|
|
clc
|
|
ror
|
|
sta COLUPF
|
|
jmp nextframe
|
|
|
|
; SetHorizPos - Sets the horizontal position of an object.
|
|
; The X register contains the index of the desired object:
|
|
; X=0: player 0
|
|
; X=1: player 1
|
|
; X=2: missile 0
|
|
; X=3: missile 1
|
|
; X=4: ball
|
|
; This routine does a WSYNC and HMOVE before executing,
|
|
; so whatever you do here will not take effect until you
|
|
; call the routine again or do your own WSYNC and HMOVE.
|
|
SetHorizPos
|
|
sta WSYNC ; start a new line
|
|
sta HMOVE ; apply the previous fine position(s)
|
|
sta HMCLR ; reset the old horizontal position(s)
|
|
sec ; set carry flag
|
|
DivideLoop
|
|
sbc #15 ; subtract 15
|
|
bcs DivideLoop ; branch until negative
|
|
eor #7 ; calculate fine offset
|
|
asl
|
|
asl
|
|
asl
|
|
asl
|
|
sta RESP0,x ; fix coarse position
|
|
sta HMP0,x ; set fine offset
|
|
rts ; return to caller
|
|
|
|
; Hard-coded values for movement registers
|
|
MOVEMENT
|
|
.byte $f0 ; +1 pixels
|
|
.byte $e0 ; +2 pixels
|
|
.byte $c0 ; +4 pixels
|
|
.byte $10 ; -1 pixels
|
|
.byte $20 ; -2 pixels
|
|
|
|
; Bitmap pattern for digits
|
|
NUMBERS ;;{w:8,h:6,count:10,brev:1};;
|
|
.byte $EE,$AA,$AA,$AA,$EE,$00
|
|
.byte $22,$22,$22,$22,$22,$00
|
|
.byte $EE,$22,$EE,$88,$EE,$00
|
|
.byte $EE,$22,$66,$22,$EE,$00
|
|
.byte $AA,$AA,$EE,$22,$22,$00
|
|
.byte $EE,$88,$EE,$22,$EE,$00
|
|
.byte $EE,$88,$EE,$AA,$EE,$00
|
|
.byte $EE,$22,$22,$22,$22,$00
|
|
.byte $EE,$AA,$EE,$AA,$EE,$00
|
|
.byte $EE,$AA,$EE,$22,$EE,$00
|
|
|
|
; Epilogue
|
|
org $fffc
|
|
.word start
|
|
.word start
|