Applecorn/auxmem.gfx.s
2021-09-20 18:54:33 -04:00

113 lines
3.0 KiB
ArmAsm

* AUXMEM.GFX.S
* (c) Bobbi 2021 GPLv3
*
* Graphics operations
* 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
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
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
ROR ZP2+0
CLC ; ZP2 divide by 2
ROR ZP2+1
ROR ZP2+0
LDA ZP2+0
STA VDUQ+7
LDA ZP2+1
STA VDUQ+8
RTS
* Add coordinates to XPIXEL, YPIXEL
RELCOORD CLC
LDA XPIXEL+0
ADC VDUQ+5
STA VDUQ+5
LDA XPIXEL+1
ADC VDUQ+6
STA VDUQ+6
CLC
LDA YPIXEL
ADC VDUQ+7
STA VDUQ+7
RTS