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mode7: more timing info

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This commit is contained in:
Vince Weaver 2017-12-31 17:12:52 -05:00
parent f6601e3d16
commit 008c3b3d1f
1 changed files with 21 additions and 20 deletions
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41
mode7/starfield_demo.s
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@ -66,8 +66,8 @@ draw_stars:
lda #$ff ; want if z<16, color = 5 ; 2
sta COLOR ; if 16<z<32 color = 13 ; 3
; if 32<z<64 color = 15
ldy XX ; 3
lda star_z,Y ; 5
lda star_z,X ; 4
tay ; put star_z[i] in X for later ; 2
cmp #32 ; 2
@ -94,31 +94,32 @@ done_color:
lda z_table,Y ; 4
sta NUM1L ; F ; 3
; adjust for 58+
; adjust spacez for 58+
; all this logic to avoid having a 128 byte table of mostly zero
lda #0 ; I
clc
cpy #60 ; 59 -1 60 0 61 1
bmi no_adjust
adc #1 ; 60, 61 = 1
cpy #62 ; 61 -1 62 0 63 1
bmi no_adjust
adc #1 ; 62 = 2
cpy #63 ; 62 = -1 63 = 0 64 = not possible
bne no_adjust
adc #2 ; 63 = 4
lda #0 ; I ; 2
clc ; 2
cpy #60 ; 59 -1 60 0 61 1 ; 2
bmi no_adjust ; 2nt/3
adc #1 ; 60, 61 = 1 ; 2
cpy #62 ; 61 -1 62 0 63 1 ; 2
bmi no_adjust ; 2nt/3
adc #1 ; 62 = 2 ; 2
cpy #63 ; 62 = -1 63 = 0 64 = not possible ; 2
bne no_adjust ; 2nt/3
adc #2 ; 63 = 4 ; 2
no_adjust:
sta NUM1H
sta NUM1H ; store int part of spacez ; 3
; load stars[i].x into NUM2H:NUM2L
; NUM2L is always zero
ldy XX
ldy XX ; 3
lda star_x,Y
sta NUM2H
lda star_x,Y ; 4
sta NUM2H ; 3
lda #0
sta NUM2L
lda #0 ; 2
sta NUM2L ; 3
sec ; don't reuse old values
jsr multiply