133 lines
3.8 KiB
Plaintext
133 lines
3.8 KiB
Plaintext
# Use the built-in font to draw a grapheme to real screen.
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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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#
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# There are uncomfortable assumptions baked in here about english/latin
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# script. We convert the grid of pixels into a fixed-width grid of graphemes,
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# which may not work well with other language families.
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== code
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# The Mu computer's screen is 1024px wide and 768px tall.
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# The Mu computer's font is 8px wide and 16px tall.
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# Therefore 'x' here is in [0, 128), and 'y' is in [0, 48)
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draw-grapheme-on-real-screen: # g: grapheme, x: int, y: int, color: int, background-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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52/push-edx
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53/push-ebx
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56/push-esi
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# var letter-bitmap/esi = font[g]
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8b/-> *(ebp+8) 6/r32/esi
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c1 4/subop/shift-left %esi 4/imm8
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8d/copy-address *(esi+0x8800) 6/r32/esi # font-start
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# if (letter-bitmap >= 0x9000) return # characters beyond ASCII currently not supported
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81 7/subop/compare %esi 0x9000/imm32
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7d/jump-if->= $draw-grapheme-on-real-screen:end/disp8
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# var ycurr/edx: int = y*16
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8b/-> *(ebp+0x10) 2/r32/edx
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c1 4/subop/shift-left %edx 4/imm8
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# var ymax/ebx: int = ycurr + 16
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8b/-> *(ebp+0x10) 3/r32/ebx
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c1 4/subop/shift-left %ebx 4/imm8
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81 0/subop/add %ebx 0x10/imm32
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{
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# if (ycurr >= ymax) break
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39/compare %edx 3/r32/ebx
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7d/jump-if->= break/disp8
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# var xcurr/eax: int = x*8 + 7
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8b/-> *(ebp+0xc) 0/r32/eax # font-width - 1
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c1 4/subop/shift-left %eax 3/imm8
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81 0/subop/add %eax 7/imm32
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# var xmin/ecx: int = x*8
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8b/-> *(ebp+0xc) 1/r32/ecx
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c1 4/subop/shift-left %ecx 3/imm8
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# var row-bitmap/ebx: int = *letter-bitmap
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53/push-ebx
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8b/-> *esi 3/r32/ebx
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{
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# if (xcurr < xmin) break
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39/compare %eax 1/r32/ecx
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7c/jump-if-< break/disp8
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# shift LSB from row-bitmap into carry flag (CF)
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c1 5/subop/shift-right-logical %ebx 1/imm8
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# if LSB, draw a pixel in the given color
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{
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73/jump-if-not-CF break/disp8
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(pixel-on-real-screen %eax %edx *(ebp+0x14))
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eb/jump $draw-grapheme-on-real-screen:continue/disp8
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}
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# otherwise use the background color
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(pixel-on-real-screen %eax %edx *(ebp+0x18))
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$draw-grapheme-on-real-screen:continue:
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# --x
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48/decrement-eax
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#
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eb/jump loop/disp8
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}
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# reclaim row-bitmap
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5b/pop-to-ebx
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# ++y
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42/increment-edx
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# next bitmap row
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46/increment-esi
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#
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eb/jump loop/disp8
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}
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$draw-grapheme-on-real-screen:end:
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# . restore registers
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5e/pop-to-esi
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5b/pop-to-ebx
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5a/pop-to-edx
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59/pop-to-ecx
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58/pop-to-eax
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# . epilogue
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89/<- %esp 5/r32/ebp
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5d/pop-to-ebp
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c3/return
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cursor-position-on-real-screen: # -> _/eax: int, _/ecx: int
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# . prologue
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55/push-ebp
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89/<- %ebp 4/r32/esp
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# TODO: support fake screen; we currently assume 'screen' is always 0 (real)
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8b/-> *Default-next-x 0/r32/eax
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8b/-> *Default-next-y 1/r32/ecx
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$cursor-position-on-real-screen:end:
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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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set-cursor-position-on-real-screen: # x: int, y: 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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# TODO: support fake screen; we currently assume 'screen' is always 0 (real)
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8b/-> *(ebp+8) 0/r32/eax
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89/<- *Default-next-x 0/r32/eax
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8b/-> *(ebp+0xc) 0/r32/eax
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89/<- *Default-next-y 0/r32/eax
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$set-cursor-position-on-real-screen:end:
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# . restore registers
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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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== data
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Default-next-x:
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0/imm32
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Default-next-y:
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0/imm32
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