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mode7: add in some multiplies

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Vince Weaver 2017-12-30 09:40:30 -05:00
parent d1a0ac9144
commit 9e4b1c132a
1 changed files with 41 additions and 1 deletions
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42
mode7/starfield_demo.s
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@ -63,11 +63,51 @@ draw_stars:
lda #$ff
sta COLOR
; calculate x and y
; calculate x value, stars[i].x/stars[i].z
lda #20
ldy #20
lda #0 ; I
sta NUM1H
lda #0 ; F
sta NUM1L
lda #1
sta NUM2H
lda #2
sta NUM2L
sec ; don't reuse old values
jsr multiply
; integer result in X
txa
clc
adc #20
sta XX
; calculate y value, stars[i].y/stars[i].z
lda #0 ; I
sta NUM1H
lda #0 ; F
sta NUM1L
lda #1
sta NUM2H
lda #2
sta NUM2L
sec ; don't reuse old values
jsr multiply
; integer result in X
txa
clc
adc #20
tay ; put Y value in Y to plot
lda XX ; reload X value to plot
;================================
; plot routine
;================================