6e36ce06dd
It's not really manageable to make the fake screen pixel-oriented. Feels excessive to compare things pixel by pixel when we will mostly be writing text to screen. It'll also make expected screen assertions more difficult to manage. So I'm not sure how to make assertions about pixels for now. Instead we'll introduce fake screens at draw-grapheme.
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/imm32/1024
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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/imm32/768
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7d/jump-if->= $pixel-on-real-screen:end/disp8
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# eax = y*1024 + x
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8b/-> *(ebp+0xc) 0/r32/eax
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c1/shift 4/subop/left %eax 0xa/imm8
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03/add-> *(ebp+8) 0/r32/eax
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# eax += location of frame buffer
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03/add-> *0x7f28 0/r32/eax # unsafe
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# *eax = color
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8b/-> *(ebp+0x10) 1/r32/ecx
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88/byte<- *eax 1/r32/CL
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$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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