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<a href='https://github.com/akkartik/mu/blob/main/101screen.subx'>https://github.com/akkartik/mu/blob/main/101screen.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Primitives for screen control.</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># We need to do this in machine code because Mu doesn't have global variables</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># yet (for the start of video memory).</span>
<span id="L5" class="LineNr"> 5 </span>
<span id="L6" class="LineNr"> 6 </span>== code
<span id="L7" class="LineNr"> 7 </span>
<span id="L8" class="LineNr"> 8 </span><span class="subxFunction">pixel-on-real-screen</span>: <span class="subxComment"># x: int, y: int, color: int</span>
<span id="L9" class="LineNr"> 9 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L10" class="LineNr">10 </span> 55/push-ebp
<span id="L11" class="LineNr">11 </span> 89/<- %ebp 4/r32/esp
<span id="L12" class="LineNr">12 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L13" class="LineNr">13 </span> 50/push-eax
<span id="L14" class="LineNr">14 </span> 51/push-ecx
<span id="L15" class="LineNr">15 </span> <span class="subxComment"># bounds checks</span>
<span id="L16" class="LineNr">16 </span> 8b/-> *(ebp+8) 0/r32/eax
<span id="L17" class="LineNr">17 </span> 3d/compare-eax-and 0/imm32
<span id="L18" class="LineNr">18 </span> 7c/jump-if-< $pixel-on-real-screen:end/disp8
<span id="L19" class="LineNr">19 </span> 3d/compare-eax-and 0x400/imm32/screen-width=1024
<span id="L20" class="LineNr">20 </span> 7d/jump-if->= $pixel-on-real-screen:end/disp8
<span id="L21" class="LineNr">21 </span> 8b/-> *(ebp+0xc) 0/r32/eax
<span id="L22" class="LineNr">22 </span> 3d/compare-eax-and 0/imm32
<span id="L23" class="LineNr">23 </span> 7c/jump-if-< $pixel-on-real-screen:end/disp8
<span id="L24" class="LineNr">24 </span> 3d/compare-eax-and 0x300/imm32/screen-height=768
<span id="L25" class="LineNr">25 </span> 7d/jump-if->= $pixel-on-real-screen:end/disp8
<span id="L26" class="LineNr">26 </span> <span class="subxComment"># eax = y*1024 + x</span>
<span id="L27" class="LineNr">27 </span> 8b/-> *(ebp+0xc) 0/r32/eax
<span id="L28" class="LineNr">28 </span> c1/shift 4/subop/left %eax 0xa/imm8
<span id="L29" class="LineNr">29 </span> 03/add-> *(ebp+8) 0/r32/eax
<span id="L30" class="LineNr">30 </span> <span class="subxComment"># eax += location of frame buffer</span>
<span id="L31" class="LineNr">31 </span> 03/add-> *<span class="SpecialChar"><a href='boot.subx.html#L607'>Video-memory-addr</a></span> 0/r32/eax
<span id="L32" class="LineNr">32 </span> <span class="subxComment"># *eax = color</span>
<span id="L33" class="LineNr">33 </span> 8b/-> *(ebp+0x10) 1/r32/ecx
<span id="L34" class="LineNr">34 </span> 88/byte<- *eax 1/r32/CL
<span id="L35" class="LineNr">35 </span><span class="Constant">$pixel-on-real-screen:end</span>:
<span id="L36" class="LineNr">36 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L37" class="LineNr">37 </span> 59/pop-to-ecx
<span id="L38" class="LineNr">38 </span> 58/pop-to-eax
<span id="L39" class="LineNr">39 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L40" class="LineNr">40 </span> 89/<- %esp 5/r32/ebp
<span id="L41" class="LineNr">41 </span> 5d/pop-to-ebp
<span id="L42" class="LineNr">42 </span> c3/return
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