43 lines
1.2 KiB
Plaintext
43 lines
1.2 KiB
Plaintext
# Primitives for screen control.
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#
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# We need to do this in machine code because Mu doesn't have global variables
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# yet (for the start of video memory).
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== code
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pixel-on-real-screen: # x: int, y: int, color: int
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# . prologue
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55/push-ebp
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89/<- %ebp 4/r32/esp
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# . save registers
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50/push-eax
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51/push-ecx
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# bounds checks
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8b/-> *(ebp+8) 0/r32/eax
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3d/compare-eax-and 0/imm32
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7c/jump-if-< $pixel-on-real-screen:end/disp8
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3d/compare-eax-and 0x400/imm32/screen-width=1024
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7d/jump-if->= $pixel-on-real-screen:end/disp8
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8b/-> *(ebp+0xc) 0/r32/eax
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3d/compare-eax-and 0/imm32
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7c/jump-if-< $pixel-on-real-screen:end/disp8
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3d/compare-eax-and 0x300/imm32/screen-height=768
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7d/jump-if->= $pixel-on-real-screen:end/disp8
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# eax = y*1024 + x
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8b/-> *(ebp+0xc) 0/r32/eax
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c1/shift 4/subop/left %eax 0xa/imm8
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03/add-> *(ebp+8) 0/r32/eax
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# eax += location of frame buffer
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03/add-> *Video-memory-addr 0/r32/eax
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# *eax = color
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8b/-> *(ebp+0x10) 1/r32/ecx
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88/byte<- *eax 1/r32/CL
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$pixel-on-real-screen:end:
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# . restore registers
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59/pop-to-ecx
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58/pop-to-eax
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# . epilogue
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89/<- %esp 5/r32/ebp
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5d/pop-to-ebp
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c3/return
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