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starpath: working assembly code

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This commit is contained in:
Vince Weaver 2025-02-25 22:29:25 -05:00
parent e89e504fbf
commit 6c56c915bd
1 changed files with 12 additions and 9 deletions
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21
graphics/gr/starpath/starpath.s
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@ -59,13 +59,13 @@ loop3:
tay ; multiply Y*4*D
lda D
jsr mul8
jsr mul8 ; definitely 8-bit mul in original
sta YPH ; store out to YPH:YPL
lda PRODLO
sta YPL
lda XPOS ; XP=(X*6)-D
lda XPOS ; XP=(X*6)-D curve X by depth
asl
sta XPL
asl
@ -79,7 +79,7 @@ loop3:
sbc D
sta XPL
bpl loop4 ;IF XP<0 THEN
bcs loop4 ; IF XP<0 THEN if left then draw sky
lda #31 ; C=31
sta C
@ -96,17 +96,20 @@ loop3:
jmp loop7 ; GOTO7
loop4:
; Q=XP*D/256
; Q=XP*D/256 multiply X by current depth
; want high part
; definitely 8-bit mul
ldy XPL
lda D
jsr mul8
ora YPH ; R=YP/256
sta Q ; Q=ora Q,R
ora YPH ; R=YP/256
sta Q ; Q=ora Q,R
; or for texture pattern
clc
lda D ;and D+F
lda D ; add depth plus frame D+F
adc FRAME
and Q
and Q ; mask geometry by time shifted depth
sta C
inc D ; D=D+1