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<a href='https://github.com/akkartik/mu/blob/main/103grapheme.subx'>https://github.com/akkartik/mu/blob/main/103grapheme.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Use the built-in font to draw a grapheme to real screen.</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 the font).</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment">#</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># There are uncomfortable assumptions baked in here about english/latin</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># script. We convert the grid of pixels into a fixed-width grid of graphemes,</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># which may not work well with other language families.</span>
<span id="L9" class="LineNr"> 9 </span>
<span id="L10" class="LineNr"> 10 </span>== code
<span id="L11" class="LineNr"> 11 </span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment"># The Mu computer's screen is 1024px wide and 768px tall.</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxComment"># The Mu computer's font is 8px wide and 16px tall.</span>
<span id="L14" class="LineNr"> 14 </span><span class="subxComment"># Therefore 'x' here is in [0, 128), and 'y' is in [0, 48)</span>
<span id="L15" class="LineNr"> 15 </span><span class="subxComment"># Doesn't update the cursor; where the cursor should go after printing the</span>
<span id="L16" class="LineNr"> 16 </span><span class="subxComment"># current grapheme is a higher-level concern.</span>
<span id="L17" class="LineNr"> 17 </span><span class="subxFunction">draw-grapheme-on-real-screen</span>: <span class="subxComment"># g: grapheme, x: int, y: int, color: int, background-color: int</span>
<span id="L18" class="LineNr"> 18 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L19" class="LineNr"> 19 </span> 55/push-ebp
<span id="L20" class="LineNr"> 20 </span> 89/<- %ebp 4/r32/esp
<span id="L21" class="LineNr"> 21 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L22" class="LineNr"> 22 </span> 50/push-eax
<span id="L23" class="LineNr"> 23 </span> 51/push-ecx
<span id="L24" class="LineNr"> 24 </span> 52/push-edx
<span id="L25" class="LineNr"> 25 </span> 53/push-ebx
<span id="L26" class="LineNr"> 26 </span> 56/push-esi
<span id="L27" class="LineNr"> 27 </span> <span class="subxComment"># var letter-bitmap/esi = font[g]</span>
<span id="L28" class="LineNr"> 28 </span> 8b/-> *(ebp+8) 6/r32/esi
<span id="L29" class="LineNr"> 29 </span> c1 4/subop/shift-left %esi 4/imm8
<span id="L30" class="LineNr"> 30 </span> 81 0/subop/add %esi <span class="SpecialChar"><a href='boot.subx.html#L643'>Font</a></span>/imm32
<span id="L31" class="LineNr"> 31 </span> <span class="subxComment"># if (letter-bitmap >= 0x9400) return # characters beyond ASCII currently not supported</span>
<span id="L32" class="LineNr"> 32 </span> 81 7/subop/compare %esi 0x9400/imm32
<span id="L33" class="LineNr"> 33 </span> 7d/jump-if->= $draw-grapheme-on-real-screen:end/disp8
<span id="L34" class="LineNr"> 34 </span> <span class="subxComment"># var ycurr/edx: int = y*16</span>
<span id="L35" class="LineNr"> 35 </span> 8b/-> *(ebp+0x10) 2/r32/edx
<span id="L36" class="LineNr"> 36 </span> c1 4/subop/shift-left %edx 4/imm8
<span id="L37" class="LineNr"> 37 </span> <span class="subxComment"># var ymax/ebx: int = ycurr + 16</span>
<span id="L38" class="LineNr"> 38 </span> 8b/-> *(ebp+0x10) 3/r32/ebx
<span id="L39" class="LineNr"> 39 </span> c1 4/subop/shift-left %ebx 4/imm8
<span id="L40" class="LineNr"> 40 </span> 81 0/subop/add %ebx 0x10/imm32
<span id="L41" class="LineNr"> 41 </span> {
<span id="L42" class="LineNr"> 42 </span> <span class="subxComment"># if (ycurr >= ymax) break</span>
<span id="L43" class="LineNr"> 43 </span> 39/compare %edx 3/r32/ebx
<span id="L44" class="LineNr"> 44 </span> 7d/jump-if->= <span class="Constant">break</span>/disp8
<span id="L45" class="LineNr"> 45 </span> <span class="subxComment"># var xcurr/eax: int = x*8 + 7</span>
<span id="L46" class="LineNr"> 46 </span> 8b/-> *(ebp+0xc) 0/r32/eax <span class="subxComment"># font-width - 1</span>
<span id="L47" class="LineNr"> 47 </span> c1 4/subop/shift-left %eax 3/imm8
<span id="L48" class="LineNr"> 48 </span> 81 0/subop/add %eax 7/imm32
<span id="L49" class="LineNr"> 49 </span> <span class="subxComment"># var xmin/ecx: int = x*8</span>
<span id="L50" class="LineNr"> 50 </span> 8b/-> *(ebp+0xc) 1/r32/ecx
<span id="L51" class="LineNr"> 51 </span> c1 4/subop/shift-left %ecx 3/imm8
<span id="L52" class="LineNr"> 52 </span> <span class="subxComment"># var row-bitmap/ebx: int = *letter-bitmap</span>
<span id="L53" class="LineNr"> 53 </span> 53/push-ebx
<span id="L54" class="LineNr"> 54 </span> 8b/-> *esi 3/r32/ebx
<span id="L55" class="LineNr"> 55 </span> {
<span id="L56" class="LineNr"> 56 </span> <span class="subxComment"># if (xcurr < xmin) break</span>
<span id="L57" class="LineNr"> 57 </span> 39/compare %eax 1/r32/ecx
<span id="L58" class="LineNr"> 58 </span> 7c/jump-if-< <span class="Constant">break</span>/disp8
<span id="L59" class="LineNr"> 59 </span> <span class="subxComment"># shift LSB from row-bitmap into carry flag (CF)</span>
<span id="L60" class="LineNr"> 60 </span> c1 5/subop/shift-right-logical %ebx 1/imm8
<span id="L61" class="LineNr"> 61 </span> <span class="subxComment"># if LSB, draw a pixel in the given color</span>
<span id="L62" class="LineNr"> 62 </span> {
<span id="L63" class="LineNr"> 63 </span> 73/jump-if-not-CF <span class="Constant">break</span>/disp8
<span id="L64" class="LineNr"> 64 </span> (<a href='101screen.subx.html#L8'>pixel-on-real-screen</a> %eax %edx *(ebp+0x14))
<span id="L65" class="LineNr"> 65 </span> eb/jump $draw-grapheme-on-real-screen:continue/disp8
<span id="L66" class="LineNr"> 66 </span> }
<span id="L67" class="LineNr"> 67 </span> <span class="subxComment"># otherwise use the background color</span>
<span id="L68" class="LineNr"> 68 </span> (<a href='101screen.subx.html#L8'>pixel-on-real-screen</a> %eax %edx *(ebp+0x18))
<span id="L69" class="LineNr"> 69 </span><span class="Constant">$draw-grapheme-on-real-screen:continue</span>:
<span id="L70" class="LineNr"> 70 </span> <span class="subxComment"># --x</span>
<span id="L71" class="LineNr"> 71 </span> 48/decrement-eax
<span id="L72" class="LineNr"> 72 </span> <span class="subxComment">#</span>
<span id="L73" class="LineNr"> 73 </span> eb/jump <span class="Constant">loop</span>/disp8
<span id="L74" class="LineNr"> 74 </span> }
<span id="L75" class="LineNr"> 75 </span> <span class="subxComment"># reclaim row-bitmap</span>
<span id="L76" class="LineNr"> 76 </span> 5b/pop-to-ebx
<span id="L77" class="LineNr"> 77 </span> <span class="subxComment"># ++y</span>
<span id="L78" class="LineNr"> 78 </span> 42/increment-edx
<span id="L79" class="LineNr"> 79 </span> <span class="subxComment"># next bitmap row</span>
<span id="L80" class="LineNr"> 80 </span> 46/increment-esi
<span id="L81" class="LineNr"> 81 </span> <span class="subxComment">#</span>
<span id="L82" class="LineNr"> 82 </span> eb/jump <span class="Constant">loop</span>/disp8
<span id="L83" class="LineNr"> 83 </span> }
<span id="L84" class="LineNr"> 84 </span><span class="Constant">$draw-grapheme-on-real-screen:end</span>:
<span id="L85" class="LineNr"> 85 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L86" class="LineNr"> 86 </span> 5e/pop-to-esi
<span id="L87" class="LineNr"> 87 </span> 5b/pop-to-ebx
<span id="L88" class="LineNr"> 88 </span> 5a/pop-to-edx
<span id="L89" class="LineNr"> 89 </span> 59/pop-to-ecx
<span id="L90" class="LineNr"> 90 </span> 58/pop-to-eax
<span id="L91" class="LineNr"> 91 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L92" class="LineNr"> 92 </span> 89/<- %esp 5/r32/ebp
<span id="L93" class="LineNr"> 93 </span> 5d/pop-to-ebp
<span id="L94" class="LineNr"> 94 </span> c3/return
<span id="L95" class="LineNr"> 95 </span>
<span id="L96" class="LineNr"> 96 </span><span class="subxFunction">cursor-position-on-real-screen</span>: <span class="subxComment"># -> _/eax: int, _/ecx: int</span>
<span id="L97" class="LineNr"> 97 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L98" class="LineNr"> 98 </span> 55/push-ebp
<span id="L99" class="LineNr"> 99 </span> 89/<- %ebp 4/r32/esp
<span id="L100" class="LineNr">100 </span> <span class="subxComment"># TODO: support fake screen; we currently assume 'screen' is always 0 (real)</span>
<span id="L101" class="LineNr">101 </span> 8b/-> *<span class="SpecialChar"><a href='103grapheme.subx.html#L170'>Real-screen-cursor-x</a></span> 0/r32/eax
<span id="L102" class="LineNr">102 </span> 8b/-> *<span class="SpecialChar"><a href='103grapheme.subx.html#L172'>Real-screen-cursor-y</a></span> 1/r32/ecx
<span id="L103" class="LineNr">103 </span><span class="Constant">$cursor-position-on-real-screen:end</span>:
<span id="L104" class="LineNr">104 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L105" class="LineNr">105 </span> 89/<- %esp 5/r32/ebp
<span id="L106" class="LineNr">106 </span> 5d/pop-to-ebp
<span id="L107" class="LineNr">107 </span> c3/return
<span id="L108" class="LineNr">108 </span>
<span id="L109" class="LineNr">109 </span><span class="subxFunction">set-cursor-position-on-real-screen</span>: <span class="subxComment"># x: int, y: int</span>
<span id="L110" class="LineNr">110 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L111" class="LineNr">111 </span> 55/push-ebp
<span id="L112" class="LineNr">112 </span> 89/<- %ebp 4/r32/esp
<span id="L113" class="LineNr">113 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L114" class="LineNr">114 </span> 50/push-eax
<span id="L115" class="LineNr">115 </span> <span class="subxComment">#</span>
<span id="L116" class="LineNr">116 </span> 8b/-> *(ebp+8) 0/r32/eax
<span id="L117" class="LineNr">117 </span> 89/<- *<span class="SpecialChar"><a href='103grapheme.subx.html#L170'>Real-screen-cursor-x</a></span> 0/r32/eax
<span id="L118" class="LineNr">118 </span> 8b/-> *(ebp+0xc) 0/r32/eax
<span id="L119" class="LineNr">119 </span> 89/<- *<span class="SpecialChar"><a href='103grapheme.subx.html#L172'>Real-screen-cursor-y</a></span> 0/r32/eax
<span id="L120" class="LineNr">120 </span><span class="Constant">$set-cursor-position-on-real-screen:end</span>:
<span id="L121" class="LineNr">121 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L122" class="LineNr">122 </span> 58/pop-to-eax
<span id="L123" class="LineNr">123 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L124" class="LineNr">124 </span> 89/<- %esp 5/r32/ebp
<span id="L125" class="LineNr">125 </span> 5d/pop-to-ebp
<span id="L126" class="LineNr">126 </span> c3/return
<span id="L127" class="LineNr">127 </span>
<span id="L128" class="LineNr">128 </span><span class="subxComment"># Not a real `show-cursor` primitive:</span>
<span id="L129" class="LineNr">129 </span><span class="subxComment"># - does not clear previous location cursor was shown at.</span>
<span id="L130" class="LineNr">130 </span><span class="subxComment"># - does not preserve what was at the cursor. Caller is responsible for</span>
<span id="L131" class="LineNr">131 </span><span class="subxComment"># tracking what was on the screen at this position before and passing it</span>
<span id="L132" class="LineNr">132 </span><span class="subxComment"># in again.</span>
<span id="L133" class="LineNr">133 </span><span class="subxComment"># - does not stop showing the cursor at this location when the cursor moves</span>
<span id="L134" class="LineNr">134 </span><span class="subxFunction">draw-cursor-on-real-screen</span>: <span class="subxComment"># g: grapheme</span>
<span id="L135" class="LineNr">135 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L136" class="LineNr">136 </span> 55/push-ebp
<span id="L137" class="LineNr">137 </span> 89/<- %ebp 4/r32/esp
<span id="L138" class="LineNr">138 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L139" class="LineNr">139 </span> 50/push-eax
<span id="L140" class="LineNr">140 </span> 51/push-ecx
<span id="L141" class="LineNr">141 </span> <span class="subxComment">#</span>
<span id="L142" class="LineNr">142 </span> (<a href='103grapheme.subx.html#L96'>cursor-position-on-real-screen</a>) <span class="subxComment"># => eax, ecx</span>
<span id="L143" class="LineNr">143 </span> (<a href='103grapheme.subx.html#L17'>draw-grapheme-on-real-screen</a> *(ebp+8) %eax %ecx 0 7)
<span id="L144" class="LineNr">144 </span><span class="Constant">$draw-cursor-on-real-screen:end</span>:
<span id="L145" class="LineNr">145 </span> <span class="subxS1Comment"># . restore registers</span>
<span id="L146" class="LineNr">146 </span> 59/pop-to-ecx
<span id="L147" class="LineNr">147 </span> 58/pop-to-eax
<span id="L148" class="LineNr">148 </span> <span class="subxS1Comment"># . epilogue</span>
<span id="L149" class="LineNr">149 </span> 89/<- %esp 5/r32/ebp
<span id="L150" class="LineNr">150 </span> 5d/pop-to-ebp
<span id="L151" class="LineNr">151 </span> c3/return
<span id="L152" class="LineNr">152 </span>
<span id="L153" class="LineNr">153 </span>== data
<span id="L154" class="LineNr">154 </span>
<span id="L155" class="LineNr">155 </span><span class="subxComment"># The cursor is where certain Mu functions (usually of the form</span>
<span id="L156" class="LineNr">156 </span><span class="subxComment"># 'draw*cursor*') print to by default.</span>
<span id="L157" class="LineNr">157 </span><span class="subxComment">#</span>
<span id="L158" class="LineNr">158 </span><span class="subxComment"># We don't bother displaying the cursor when drawing. It only becomes visible</span>
<span id="L159" class="LineNr">159 </span><span class="subxComment"># on draw-cursor, which is quite rickety (see above)</span>
<span id="L160" class="LineNr">160 </span><span class="subxComment">#</span>
<span id="L161" class="LineNr">161 </span><span class="subxComment"># It's up to applications to manage cursor display:</span>
<span id="L162" class="LineNr">162 </span><span class="subxComment"># - clean up where it used to be</span>
<span id="L163" class="LineNr">163 </span><span class="subxComment"># - display the cursor before waiting for a key</span>
<span id="L164" class="LineNr">164 </span><span class="subxComment"># - ensure its location appropriately suggests the effect keystrokes will have</span>
<span id="L165" class="LineNr">165 </span><span class="subxComment"># - ensure its contents (and colors) appropriately reflect the state of the</span>
<span id="L166" class="LineNr">166 </span><span class="subxComment"># screen</span>
<span id="L167" class="LineNr">167 </span><span class="subxComment">#</span>
<span id="L168" class="LineNr">168 </span><span class="subxComment"># There's no blinking, etc. We aren't using any hardware-supported text mode</span>
<span id="L169" class="LineNr">169 </span><span class="subxComment"># here.</span>
<span id="L170" class="LineNr">170 </span><span class="SpecialChar">Real-screen-cursor-x</span>:
<span id="L171" class="LineNr">171 </span> 0/imm32
<span id="L172" class="LineNr">172 </span><span class="SpecialChar">Real-screen-cursor-y</span>:
<span id="L173" class="LineNr">173 </span> 0/imm32
</pre>
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