mirror of
https://github.com/bobbimanners/Applecorn.git
synced 2024-06-30 01:29:43 +00:00
99 lines
2.8 KiB
ArmAsm
99 lines
2.8 KiB
ArmAsm
* AUXMEM.GFX.S
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* (c) Bobbi 2021 GPLv3
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*
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* Graphics operations
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* Convert high-resolution screen coordinates
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* from 1280x1024 to 280x192
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CVTCOORD
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* X-coordinate in VDUQ+5,+6 1280/4*7/8=280
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LDA VDUQ+5 ; X-coord -> ZP1 and ZP2
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STA ZP1+0
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STA ZP2+0
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LDA VDUQ+6
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STA ZP1+1
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STA ZP2+1
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CLC ; ZP1 divide by 2 (0-639 now)
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ROR ZP1+1
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ROR ZP1+0
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CLC ; ZP1 divide by 2 (0-319 now)
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ROR ZP1+1
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ROR ZP1+0
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CLC ; ZP1+ZP2->ZP2
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LDA ZP1+0
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ADC ZP2+0
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STA ZP2+0
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LDA ZP1+1
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ADC ZP2+1
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STA ZP2+1
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CLC ; ZP1+ZP2->ZP2
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LDA ZP1+0
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ADC ZP2+0
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STA ZP2+0
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LDA ZP1+1
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ADC ZP2+1
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STA ZP2+1
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CLC ; ZP1+ZP2->ZP2
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LDA ZP1+0
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ADC ZP2+0
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STA ZP2+0
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LDA ZP1+1
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ADC ZP2+1
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STA ZP2+1
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CLC ; ZP2 divide by 2
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ROR ZP2+1
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ROR ZP2+0
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CLC ; ZP2 divide by 2
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ROR ZP2+1
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ROR ZP2+0
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CLC ; ZP2 divide by 2
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ROR ZP2+1
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ROR ZP2+0
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LDA ZP2+0
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STA VDUQ+5
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LDA ZP2+1
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STA VDUQ+6
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* Y-coordinate in VDUQ+7,+8 1024/4*3/4=192
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LDA VDUQ+7 ; Y-coord -> ZP1
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STA ZP1+0
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LDA VDUQ+8
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STA ZP1+1
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CLC ; ZP1 divide by 2 (0-512 now)
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ROR ZP1+1
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ROR ZP1+0
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CLC ; ZP1 divide by 2 (0-256 now)
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ROR ZP1+1
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ROR ZP1+0
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LDA ZP1+0 ; Copy ZP1->ZP2
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STA ZP2+0
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LDA ZP1+1
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STA ZP2+1
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CLC ; ZP1+ZP2->ZP2
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LDA ZP1+0
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ADC ZP2+0
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STA ZP2+0
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LDA ZP1+1
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ADC ZP2+1
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STA ZP2+1
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CLC ; ZP1+ZP2->ZP2
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LDA ZP1+0
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ADC ZP2+0
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STA ZP2+0
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LDA ZP1+1
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ADC ZP2+1
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STA ZP2+1
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CLC ; ZP2 divide by 2
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ROR ZP2+1
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ROR ZP2+0
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CLC ; ZP2 divide by 2
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ROR ZP2+1
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ROR ZP2+0
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LDA ZP2+0
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STA VDUQ+7
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LDA ZP2+1
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STA VDUQ+8
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RTS
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