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Faster and smaller coordinate conversion (thx @xot)

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Bobbi Webber-Manners 2021-09-21 17:02:20 -04:00
parent 0c5425611c
commit a485abfc77
2 changed files with 47 additions and 80 deletions
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@ -6,94 +6,61 @@
* Convert high-resolution screen coordinates
* from 1280x1024 to 280x192
CVTCOORD
* X-coordinate in VDUQ+5,+6 1280/4*7/8=280
LDA VDUQ+5 ; X-coord -> ZP1 and ZP2
STA ZP1+0
STA ZP2+0
LDA VDUQ+6
* X-coordinate in VDUQ+5,+6 1280*7/32=280
LDA VDUQ+6 ; X-coord -> ZP1 and ZP2
STA ZP1+1
STA ZP2+1
CLC ; ZP1 divide by 2 (0-639 now)
ROR ZP1+1
ROR ZP1+0
CLC ; ZP1 divide by 2 (0-319 now)
ROR ZP1+1
ROR ZP1+0
CLC ; ZP1+ZP2->ZP2
LDA ZP1+0
ADC ZP2+0
LDA VDUQ+5
STA ZP1+0
ASL A ; ZP2 *= 8
ROL ZP2+1
ASL A
ROL ZP2+1
ASL A
ROL ZP2+1
SEC ; ZP2-ZP1->ZP2
SBC ZP1+0
STA ZP2+0
LDA ZP1+1
ADC ZP2+1
STA ZP2+1
CLC ; ZP1+ZP2->ZP2
LDA ZP1+0
ADC ZP2+0
STA ZP2+0
LDA ZP1+1
ADC ZP2+1
STA ZP2+1
CLC ; ZP1+ZP2->ZP2
LDA ZP1+0
ADC ZP2+0
STA ZP2+0
LDA ZP1+1
ADC ZP2+1
STA ZP2+1
CLC ; ZP2 divide by 2
ROR ZP2+1
ROR ZP2+0
CLC ; ZP2 divide by 2
ROR ZP2+1
ROR ZP2+0
CLC ; ZP2 divide by 2
ROR ZP2+1
ROR ZP2+0
LDA ZP2+0
STA VDUQ+5
LDA ZP2+1
STA VDUQ+6
* Y-coordinate in VDUQ+7,+8 1024/4*3/4=192
LDA VDUQ+7 ; Y-coord -> ZP1
STA ZP1+0
LDA VDUQ+8
STA ZP1+1
CLC ; ZP1 divide by 2 (0-512 now)
ROR ZP1+1
ROR ZP1+0
CLC ; ZP1 divide by 2 (0-256 now)
ROR ZP1+1
ROR ZP1+0
LDA ZP1+0 ; Copy ZP1->ZP2
STA ZP2+0
LDA ZP1+1
STA ZP2+1
CLC ; ZP1+ZP2->ZP2
LDA ZP1+0
ADC ZP2+0
STA ZP2+0
LDA ZP1+1
ADC ZP2+1
STA ZP2+1
CLC ; ZP1+ZP2->ZP2
LDA ZP1+0
ADC ZP2+0
STA ZP2+0
LDA ZP1+1
ADC ZP2+1
STA ZP2+1
CLC ; ZP2 divide by 2
ROR ZP2+1
SBC ZP1+1
LSR A ; ZP2 /= 32
ROR ZP2+0
CLC ; ZP2 divide by 2
ROR ZP2+1
LSR A
ROR ZP2+0
LSR A
ROR ZP2+0
LSR A
ROR ZP2+0
LSR A
ROR ZP2+0
STA VDUQ+6 ; ZP2 -> X-coord
LDA ZP2+0
STA VDUQ+5
* Y-coordinate in VDUQ+7,+8 1024*3/16=192
LDA VDUQ+8 ; Y-coord -> ZP1
STA ZP1+1
STA ZP2+1
LDA VDUQ+7
STA ZP1+0
ASL A ; ZP2 *= 2
ROL ZP2+1
CLC ; ZP2+ZP1->ZP2
ADC ZP1+0
STA ZP2+0
LDA ZP2+1
ADC ZP1+1
LSR A ; ZP2 /= 16
ROR ZP2+0
LSR A
ROR ZP2+0
LSR A
ROR ZP2+0
LSR A
STA VDUQ+8 ; ZP2 -> Y-coord
LDA ZP2+0
ROR
STA VDUQ+7
LDA ZP2+1
STA VDUQ+8
RTS
* Add coordinates to XPIXEL, YPIXEL