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mode7: more work on starfield

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This commit is contained in:
Vince Weaver 2017-12-30 10:04:22 -05:00
parent 9e4b1c132a
commit 04205b7d2b
1 changed files with 20 additions and 8 deletions
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28
mode7/starfield_demo.s
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@ -55,6 +55,7 @@ starfield_loop:
ldx #NUMSTARS
draw_stars:
stx XX
txa
tay
@ -63,19 +64,28 @@ draw_stars:
lda #$ff
sta COLOR
sty YPOS
; calculate x value, stars[i].x/stars[i].z
; put 1/stars[i].z in NUM1H:NUM1L and multiply
lda #20
ldy #20
ldy YPOS
sty XPOS
lda star_z,Y
sta NUM1H ; I
lda #0 ; I
sta NUM1H
lda #0 ; F
sta NUM1L
lda #1
; load stars[i].x into NUM2H:NUM2L
; NUM2L is always zero
lda star_x,Y
sta NUM2H
lda #2
lda #0
sta NUM2L
sec ; don't reuse old values
jsr multiply
@ -84,7 +94,8 @@ draw_stars:
txa
clc
adc #20
sta XX
; sta XPOS
; calculate y value, stars[i].y/stars[i].z
@ -106,7 +117,7 @@ draw_stars:
adc #20
tay ; put Y value in Y to plot
lda XX ; reload X value to plot
lda XPOS ; reload X value to plot
;================================
; plot routine
@ -151,6 +162,7 @@ plot_write:
;==============================
ldx XX
dex
bpl draw_stars