From 2f7cde4e441a8668d7e771f23037de92ff051940 Mon Sep 17 00:00:00 2001
From: timbogdanov <hello@uchurn.com>
Date: Tue, 18 Aug 2026 21:04:01 -0500
Subject: [PATCH] Port the parametric DSL into the editor
MIME-Version: 1.0
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15 primitives, each with a declared period, composed with set/union/intersect/
xor/subtract and sized to a common multiple of every layer's period so the result
tiles seamlessly by construction. tools/dsl_prototype.py has been the reference
implementation since before the editor existed and tools/dsl_demo.py has proved
28 programs tile exactly on every commit; none of it had ever reached a user.

A Program panel makes it usable by hand: five presets, the program as editable
JSON, live size and ink readout, and a Replace canvas that renders into a
two-colour document. Bad input reports and does not crash — an unknown shape type
says so, malformed JSON says where.

Four things in the Python do not survive a literal translation, and each is a
silent wrong answer rather than an error. They are named at the top of the ported
block:

  round()   banker's rounding, so round(2.5) is 2 where Math.round gives 3. It
            decides wave offsets and canvas sizing.
  %         a floor modulo in Python, a remainder in JS. Every expression that
            can go negative routes through floorMod.
  //        floors, where |0 truncates toward zero.
  _hash2    multiplies by constants near 2^31, which passes 2^53 and silently
            drops low bits, so the mixing steps use Math.imul.

tests/fixtures/dsl.json is the oracle: 62 programs — the 28 from the gallery,
every primitive again at non-default parameters, every composition op over the
same two shapes, and every post transform on an asymmetric source — compared as
encoded patternData, because a one-pixel difference still changes the string.

59 of the 62 passed on the first run. The three failures were all `text`, and the
cause was that the glyph tables had been typed in by hand rather than taken from
the emitted file: one wrong row in the 5x7 'D' and half of 3x5 rewritten. They
are now emitted from the source tables, and the fixture carries those tables so a
future slip is reported as "5x7 font: 1/36 glyphs differ (D)" rather than as a
lit-pixel count being off by sixteen.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UCrKKTD2mwHx8Fm1EnJiQ3
---
 app/patternfront.html     |  336 +++++
 tests/fixtures/dsl.json   | 2430 +++++++++++++++++++++++++++++++++++++
 tools/gen-dsl-fixtures.py |  188 +++
 tools/verify-all.sh       |    2 +
 tools/verify-dsl.js       |  142 +++
 5 files changed, 3098 insertions(+)
 create mode 100644 tests/fixtures/dsl.json
 create mode 100644 tools/gen-dsl-fixtures.py
 create mode 100644 tools/verify-dsl.js

diff --git a/app/patternfront.html b/app/patternfront.html
index 0691d22..9f64774 100644
--- a/app/patternfront.html
+++ b/app/patternfront.html
@@ -349,6 +349,7 @@
     <button class="b sq" id="zen" title="Hide the side panels  (Tab)">
       <svg viewBox="0 0 20 20"><path d="M3 4h14v12H3z"/><path d="M7 4v12M13 4v12"/></svg></button>
     <button class="b sq" id="helpBtn" title="Shortcuts  (?)">?</button>
+    <button class="b" id="dslBtn" title="Describe a pattern as a program">Program…</button>
     <button class="b" id="imgBtn">Image…</button>
     <button class="b go" id="expBtn">Export…</button>
   </div>
@@ -537,6 +538,20 @@
     <button class="b go" id="iReplace">Replace canvas</button></div>
 </div></div>
 
+<div class="ov" id="ovDsl" hidden><div class="sheet sm">
+  <div class="sh"><h2>Program</h2><button class="b" id="dslX">Close</button></div>
+  <div style="padding:8px;display:flex;flex-direction:column;gap:7px">
+    <span class="note">A pattern described rather than drawn. The canvas is sized to a
+      common multiple of every layer's period, so the result tiles seamlessly.</span>
+    <div class="r" id="dslPresets"></div>
+    <textarea id="dslSrc" spellcheck="false" rows="12" style="width:100%;resize:vertical;
+      background:var(--well);color:var(--text);border:0.1rem solid var(--edge-dim);
+      font:inherit;padding:0.4rem"></textarea>
+    <button class="b go" id="dslGo">Replace canvas</button>
+    <span class="note" id="dslStat"></span>
+  </div>
+</div></div>
+
 <div class="ov" id="ovExp" hidden><div class="sheet sm">
   <div class="sh"><h2>Export</h2><button class="b" id="expX">Close</button></div>
   <div style="padding:8px;display:flex;flex-direction:column;gap:7px">
@@ -1609,6 +1624,64 @@
 const openOv=id=>{$(id).hidden=false;};
 const closeOv=id=>{$(id).hidden=true;};
 $('imgBtn').onclick=()=>openOv('ovImg');
+
+/* The program panel. Everything here runs against the same dslRender the
+   verification suite holds byte-for-byte against the Python oracle, so what is
+   rendered in the panel is what the fixtures cover. */
+const DSL_PRESETS={
+  Stripes:{canvas:{width:32,height:32,scale:1,autoSize:true},
+    layers:[{op:'set',shape:{type:'stripes',axis:'v',period:8,thickness:4}}],post:{}},
+  Diagonal:{canvas:{width:32,height:32,scale:1,autoSize:true},
+    layers:[{op:'set',shape:{type:'diagonal',dx:1,dy:1,period:8,thickness:3}}],post:{}},
+  Checker:{canvas:{width:32,height:32,scale:1,autoSize:true},
+    layers:[{op:'set',shape:{type:'checker',cellW:4,cellH:4}}],post:{}},
+  Plaid:{canvas:{width:32,height:32,scale:1,autoSize:true},
+    layers:[{op:'set',shape:{type:'stripes',axis:'v',period:8,thickness:3}},
+            {op:'xor',shape:{type:'stripes',axis:'h',period:6,thickness:2}}],post:{}},
+  Houndstooth:{canvas:{width:32,height:32,scale:1,autoSize:true},
+    layers:[{op:'set',shape:{type:'checker',cellW:4,cellH:4}},
+            {op:'xor',shape:{type:'diagonal',dx:1,dy:1,period:8,thickness:4}}],post:{}},
+};
+function dslShow(prog){$('dslSrc').value=JSON.stringify(prog,null,1);dslPreviewStat();}
+function dslPreviewStat(){
+  try{
+    const r=dslRender(JSON.parse($('dslSrc').value));
+    const ink=r.bits.reduce((a,b)=>a+b,0);
+    $('dslStat').innerHTML='<span style="color:var(--ok)">'+r.w+'×'+r.h+
+      ' · '+Math.round(100*ink/(r.w*r.h))+'% ink · scale '+(1<<r.scale)+'×</span>';
+  }catch(e){
+    $('dslStat').innerHTML='<span style="color:var(--danger)">'+e.message+'</span>';}
+}
+(()=>{const el=$('dslPresets');
+  for(const name of Object.keys(DSL_PRESETS)){
+    const b=document.createElement('button');b.className='b';b.textContent=name;
+    b.onclick=()=>dslShow(DSL_PRESETS[name]);el.appendChild(b);}})();
+$('dslBtn').onclick=()=>{
+  if(!$('dslSrc').value.trim()) dslShow(DSL_PRESETS.Diagonal);
+  openOv('ovDsl');dslPreviewStat();};
+$('dslX').onclick=()=>closeOv('ovDsl');
+$('ovDsl').addEventListener('pointerdown',e=>{if(e.target===$('ovDsl'))closeOv('ovDsl');});
+$('dslSrc').oninput=dslPreviewStat;
+$('dslGo').onclick=()=>{
+  let r;
+  try{ r=dslRender(JSON.parse($('dslSrc').value)); }
+  catch(e){ $('dslStat').innerHTML='<span style="color:var(--danger)">'+e.message+'</span>'; return; }
+  snap();
+  doc.w=r.w;doc.h=r.h;
+  // A program is one bit per pixel, which is the two-colour document exactly:
+  // slot 1 is the primary the format calls bit 0, slot 2 the secondary. Keep an
+  // existing duotone rather than resetting the user's colours.
+  if(doc.palette.length!==3)
+    doc.palette=[{r:0,g:0,b:0,a:0},{r:255,g:255,b:255,a:255},{r:0,g:0,b:0,a:255}];
+  doc.layers=[{name:'Program',visible:true,locked:false,opacity:1}];
+  const idx=new Uint8Array(r.w*r.h);
+  for(let i=0;i<idx.length;i++) idx[i]=r.bits[i]?2:1;
+  doc.frames=[{cels:[idx]}];
+  aLayer=0;aFrame=0;fg=2;bg=1;sel=null;
+  $('cw').value=doc.w;$('ch').value=doc.h;
+  const sl=$('ofScale'); if(sl){sl.value=r.scale;}
+  fullSync();commit();closeOv('ovDsl');
+  toast('Rendered '+r.w+'×'+r.h+' from the program');};
 $('imgX').onclick=()=>closeOv('ovImg');
 $('ovImg').addEventListener('pointerdown',e=>{if(e.target===$('ovImg'))closeOv('ovImg');});
 $('drop').onclick=()=>$('file').click();
@@ -1819,6 +1892,269 @@
   const px=floorMod(wx>>d.scale,d.w),py=floorMod(wy>>d.scale,d.h);
   return d.bits[py*d.w+px]===0;
 }
+
+/* ═══════ pattern DSL ═══════
+   A pattern described as a program rather than drawn: 15 primitives, each with a
+   declared period, composed with set/union/intersect/xor/subtract and sized so
+   the result tiles seamlessly by construction. Ported from tools/dsl_prototype.py,
+   which tools/dsl_demo.py proves tiles 28/28, and held byte-for-byte against
+   tests/fixtures/dsl.json.
+
+   Four things do NOT survive a literal translation from Python, and every one of
+   them is a silent wrong answer rather than an error:
+
+     * `round()` is banker's rounding — round(2.5) is 2, round(3.5) is 4 —
+       where Math.round always goes up. It decides wave offsets and canvas
+       sizing, so pyRound() below reproduces it.
+     * `%` is a floor modulo in Python and a remainder in JS. Any expression
+       that can go negative (a diagonal's x*dy - y*dx, a wave's y - offset)
+       needs floorMod.
+     * `//` floors; `|0` truncates toward zero. Same thing only for non-negative
+       operands, so Math.floor is used throughout rather than a bit trick.
+     * _hash2 multiplies by constants near 2^31. A plain `*` passes 2^53 and
+       silently drops low bits, so the mixing steps go through Math.imul.
+*/
+const DSL_MIN_W=2,DSL_MAX_W=129,DSL_MIN_H=2,DSL_MAX_H=65,DSL_MAX_LAYERS=4;
+
+/** Python's round(): halves go to the nearest even, not always up. */
+function pyRound(x){
+  const f=Math.floor(x),d=x-f;
+  if(d>0.5) return f+1;
+  if(d<0.5) return f;
+  return f%2===0?f:f+1;
+}
+function gcd(a,b){a=Math.abs(a);b=Math.abs(b);while(b){const t=a%b;a=b;b=t;}return a||1;}
+function lcm(a,b){return Math.abs(a*b)/gcd(a,b);}
+
+/** Deterministic [0,1). Stable across languages, which is why noise fixtures work. */
+function hash2(x,y,seed){
+  let h=(Math.imul(x,374761393)+Math.imul(y,668265263)+Math.imul(seed,2246822519))>>>0;
+  h=Math.imul(h^(h>>>13),1274126177)>>>0;
+  return ((h^(h>>>16))>>>0)/4294967296;
+}
+
+/* Bitmap fonts for the `text` primitive: one integer per row, MSB-leftmost. */
+const F57={0:[14,17,19,21,25,17,14],1:[4,12,4,4,4,4,14],2:[14,17,1,2,4,8,31],3:[31,2,4,2,1,17,14],4:[2,6,10,18,31,2,2],5:[31,16,30,1,1,17,14],6:[6,8,16,30,17,17,14],7:[31,1,2,4,8,8,8],8:[14,17,17,14,17,17,14],9:[14,17,17,15,1,2,12],A:[14,17,17,31,17,17,17],B:[30,17,17,30,17,17,30],C:[14,17,16,16,16,17,14],D:[30,17,17,17,17,17,30],E:[31,16,16,30,16,16,31],F:[31,16,16,30,16,16,16],G:[14,17,16,23,17,17,15],H:[17,17,17,31,17,17,17],I:[14,4,4,4,4,4,14],J:[7,2,2,2,2,18,12],K:[17,18,20,24,20,18,17],L:[16,16,16,16,16,16,31],M:[17,27,21,21,17,17,17],N:[17,25,21,19,17,17,17],O:[14,17,17,17,17,17,14],P:[30,17,17,30,16,16,16],Q:[14,17,17,17,21,18,13],R:[30,17,17,30,20,18,17],S:[15,16,16,14,1,1,30],T:[31,4,4,4,4,4,4],U:[17,17,17,17,17,17,14],V:[17,17,17,17,17,10,4],W:[17,17,17,21,21,27,17],X:[17,17,10,4,10,17,17],Y:[17,17,10,4,4,4,4],Z:[31,1,2,4,8,16,31]};
+const F35={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};
+
+/* Each primitive returns {fn,px,py}: fn(x,y)->0|1, genuinely periodic with the
+   declared period. Those periods are what size_canvas uses to guarantee tiling. */
+const DSL_SHAPES={
+  solid:()=>({fn:()=>1,px:1,py:1}),
+  stripes:(p)=>{
+    const period=p.period??8,phase=p.phase??0;
+    const th=Math.min(p.thickness??4,period-1);
+    return p.axis==='h'
+      ?{fn:(x,y)=>floorMod(y+phase,period)<th?1:0,px:1,py:period}
+      :{fn:(x,y)=>floorMod(x+phase,period)<th?1:0,px:period,py:1};},
+  diagonal:(p)=>{
+    const dx=p.dx??1,dy=p.dy??1,period=p.period??8,phase=p.phase??0;
+    const th=Math.min(p.thickness??4,period-1);
+    return {fn:(x,y)=>floorMod(x*dy-y*dx+phase,period)<th?1:0,
+            px:period/gcd(floorMod(dy,period)||period,period),
+            py:period/gcd(floorMod(dx,period)||period,period)};},
+  checker:(p)=>{
+    const cw=p.cellW??4,ch=p.cellH??4,phase=p.phase??0;
+    return {fn:(x,y)=>(Math.floor(x/cw)+Math.floor(y/ch)+phase)%2?1:0,
+            px:2*cw,py:2*ch};},
+  grid:(p)=>{
+    const pX=p.periodX??8,pY=p.periodY??8,fX=p.phaseX??0,fY=p.phaseY??0;
+    const lX=Math.min(p.lineX??1,pX-1),lY=Math.min(p.lineY??1,pY-1);
+    return {fn:(x,y)=>(floorMod(x+fX,pX)<lX||floorMod(y+fY,pY)<lY)?1:0,px:pX,py:pY};},
+  dots:(p)=>{
+    const pX=p.periodX??8,pY=p.periodY??8,r=p.radius??2,shape=p.shape??'circle';
+    const rowOff=p.rowOffset??0,jit=p.jitter??0,seed=p.seed??0;
+    const py=floorMod(rowOff,pX)!==0?pY*2:pY;
+    return {fn:(x,y)=>{
+      const row=Math.floor(y/pY),ox=floorMod(row*rowOff,pX);
+      let cx=floorMod(x-ox,pX)-pX/2,cy=floorMod(y,pY)-pY/2;
+      if(jit){
+        cx+=(hash2(Math.floor(x/pX),row,seed)-0.5)*2*jit;
+        cy+=(hash2(row,Math.floor(x/pX),seed+1)-0.5)*2*jit;}
+      const d=shape==='square'?Math.max(Math.abs(cx),Math.abs(cy))
+             :shape==='diamond'?Math.abs(cx)+Math.abs(cy)
+             :Math.hypot(cx,cy);
+      return d<=r?1:0;},px:pX,py};},
+  brick:(p)=>{
+    const bw=p.brickW??8,bh=p.brickH??4,mortar=p.mortar??1,off=p.offset??4;
+    return {fn:(x,y)=>{
+      const row=Math.floor(y/bh),xs=floorMod(x+row*off,bw);
+      return (floorMod(y,bh)<mortar||xs<mortar)?1:0;},
+      px:lcm(bw,bw/gcd(floorMod(off,bw)||bw,bw)),py:2*bh};},
+  wave:(p)=>{
+    const axis=p.axis??'h',period=p.period??16,amp=p.amplitude??3,phase=p.phase??0;
+    const th=p.thickness??2,vp=Math.max(2*amp,th+1);
+    const fn=axis==='h'
+      ?(x,y)=>{const o=pyRound(amp*Math.sin(2*Math.PI*floorMod(x+phase,period)/period));
+               return floorMod(y-o,vp)<th?1:0;}
+      :(x,y)=>{const o=pyRound(amp*Math.sin(2*Math.PI*floorMod(y+phase,period)/period));
+               return floorMod(x-o,vp)<th?1:0;};
+    return axis==='h'?{fn,px:period,py:vp}:{fn,px:vp,py:period};},
+  zigzag:(p)=>{
+    const axis=p.axis??'h',period=p.period??8,amp=p.amplitude??3,th=p.thickness??2;
+    const vp=Math.max(2*amp,th+1),half=period/2;
+    const tri=t=>pyRound(amp*(2*Math.abs(floorMod(t,period)/half-1)-1));
+    const fn=axis==='h'?(x,y)=>floorMod(y-tri(x),vp)<th?1:0
+                       :(x,y)=>floorMod(x-tri(y),vp)<th?1:0;
+    return axis==='h'?{fn,px:period,py:vp}:{fn,px:vp,py:period};},
+  triangles:(p)=>{
+    const size=p.size??8,down=p.orientation==='down';
+    return {fn:(x,y)=>{
+      const u=floorMod(x,2*size);
+      let v=floorMod(y,size);
+      if(down) v=size-1-v;
+      const half=size-1-v;
+      return (u>=half&&u<2*size-half)?1:0;},px:2*size,py:size};},
+  rings:(p)=>{
+    const period=p.period??16,th=p.thickness??2,cx=p.cx??0,cy=p.cy??0;
+    return {fn:(x,y)=>{
+      const u=floorMod(x+cx,period)-period/2,v=floorMod(y+cy,period)-period/2;
+      const d=Math.trunc(Math.hypot(u,v));
+      return floorMod(d,th*2)<th?1:0;},px:period,py:period};},
+  halftone:(p)=>{
+    const period=p.period??8,angle=p.angle??0;
+    const level=Math.max(0,Math.min(1,p.level??0.5));
+    const r=Math.sqrt(level)*period*0.62;
+    return {fn:(x,y)=>{
+      const xs=angle===45
+        ?floorMod(x+floorMod(Math.floor(y/period),2)*Math.floor(period/2),period)
+        :floorMod(x,period);
+      const u=xs-period/2,v=floorMod(y,period)-period/2;
+      return Math.hypot(u,v)<=r?1:0;},px:period,py:period*(angle===45?2:1)};},
+  noise:(p,canvas)=>{
+    const [w,h]=canvas,density=p.density??0.5,seed=p.seed??0;
+    let grid=[];
+    for(let y=0;y<h;y++){const row=[];
+      for(let x=0;x<w;x++) row.push(hash2(x,y,seed)<density?1:0);
+      grid.push(row);}
+    if(p.blue){
+      // Void-and-cluster, cheaply: drop any point that already has a lit
+      // 4-neighbour toroidally, which breaks up clumps.
+      const out=[];for(let y=0;y<h;y++) out.push(new Array(w).fill(0));
+      for(let y=0;y<h;y++)for(let x=0;x<w;x++){
+        if(!grid[y][x]) continue;
+        const near=[[1,0],[-1,0],[0,1],[0,-1]].some(([dx,dy])=>
+          out[floorMod(y+dy,h)][floorMod(x+dx,w)]);
+        if(!near) out[y][x]=1;}
+      grid=out;}
+    return {fn:(x,y)=>grid[floorMod(y,h)][floorMod(x,w)],px:w,py:h};},
+  text:(p)=>{
+    const font=p.font??'5x7',table=font==='5x7'?F57:F35;
+    const gwid=font==='5x7'?5:3,gh=font==='5x7'?7:5;
+    const tracking=p.tracking??1,leading=p.leading??2;
+    let chars=String(p.glyphs??'AB').toUpperCase().split('')
+      .filter(c=>Object.prototype.hasOwnProperty.call(table,c)).slice(0,8);
+    if(!chars.length) chars=['A'];
+    const total=chars.length*(gwid+tracking),vspan=gh+leading;
+    return {fn:(x,y)=>{
+      const v=floorMod(y,vspan);
+      if(v>=gh) return 0;                       // inside the leading gap
+      const u=floorMod(x,total),idx=Math.floor(u/(gwid+tracking)),col=u%(gwid+tracking);
+      if(col>=gwid||idx>=chars.length) return 0;
+      return (table[chars[idx]][v]>>(gwid-1-col))&1?1:0;},px:total,py:vspan};},
+  border:(p,canvas)=>{
+    const [w,h]=canvas,inset=p.inset??0,th=p.thickness??1;
+    return {fn:(x,y)=>{
+      const u=floorMod(x,w),v=floorMod(y,h);
+      const inner=u>=inset&&u<w-inset&&v>=inset&&v<h-inset;
+      const core=u>=inset+th&&u<w-inset-th&&v>=inset+th&&v<h-inset-th;
+      return (inner&&!core)?1:0;},px:w,py:h};},
+};
+// Their period is the canvas, not their own parameters, so they cannot drive sizing.
+const DSL_CANVAS_LOCKED=new Set(['noise','border']);
+
+/* Out-of-range values are clamped rather than rejected: a model that says
+   period 900 meant "very wide", and refusing the whole program helps nobody. */
+const DSL_RANGES={
+  period:[2,64],periodX:[2,64],periodY:[2,64],thickness:[1,63],
+  phase:[0,63],phaseX:[0,63],phaseY:[0,63],dx:[1,8],dy:[1,8],
+  cellW:[1,32],cellH:[1,32],lineX:[1,8],lineY:[1,8],radius:[0,16],
+  rowOffset:[0,63],jitter:[0,4],brickW:[2,64],brickH:[1,32],mortar:[1,4],
+  offset:[0,63],amplitude:[1,16],size:[2,32],cx:[0,63],cy:[0,63],
+  level:[0,1],density:[0,1],inset:[0,16],tracking:[0,3],leading:[0,8],
+};
+function dslValidateShape(raw){
+  if(!raw||typeof raw!=='object'||!raw.type) throw new Error("shape missing 'type'");
+  if(!DSL_SHAPES[raw.type]) throw new Error('unknown shape type '+JSON.stringify(raw.type));
+  const out={type:raw.type};
+  for(const k of Object.keys(raw)){
+    if(k==='type') continue;
+    const r=DSL_RANGES[k];
+    out[k]=r?Math.max(r[0],Math.min(r[1],raw[k])):raw[k];}
+  if('thickness' in out&&'period' in out) out.thickness=Math.min(out.thickness,out.period-1);
+  if('seed' in out) out.seed=out.seed>>>0;
+  if(raw.type==='text'){
+    const g=String(out.glyphs??'A').toUpperCase().replace(/[^A-Z0-9]/g,'').slice(0,8);
+    out.glyphs=g||'A';}
+  return out;
+}
+function dslValidate(prog){
+  if(!prog||typeof prog!=='object') throw new Error('program must be an object');
+  const layers=prog.layers||[];
+  if(!layers.length) throw new Error('program has no layers');
+  if(layers.length>DSL_MAX_LAYERS)
+    throw new Error('too many layers ('+layers.length+' > '+DSL_MAX_LAYERS+')');
+  const clean={canvas:{...(prog.canvas||{})},
+    layers:layers.map(l=>({op:l.op||'union',shape:dslValidateShape(l.shape)})),
+    post:{...(prog.post||{})}};
+  clean.layers[0].op='set';                     // nothing to compose against yet
+  return clean;
+}
+
+/* The tiling guarantee: size the canvas to a common multiple of every layer's
+   period, so the edges meet. A period wider than the format can hold cannot
+   tile, and the canvas is capped instead — the seam is then real and reported. */
+function dslSize(program){
+  const c=program.canvas||{},wantW=c.width??16,wantH=c.height??16;
+  if(c.autoSize===false)
+    return [Math.max(DSL_MIN_W,Math.min(DSL_MAX_W,wantW)),
+            Math.max(DSL_MIN_H,Math.min(DSL_MAX_H,wantH))];
+  let px=1,py=1;
+  for(const layer of program.layers){
+    const s=layer.shape;
+    if(DSL_CANVAS_LOCKED.has(s.type)) continue;
+    const {px:sx,py:sy}=DSL_SHAPES[s.type](s,[wantW,wantH]);
+    px=lcm(px,Math.max(1,sx));py=lcm(py,Math.max(1,sy));}
+  const fit=(period,want,lo,hi)=>{
+    if(period>hi) return hi;
+    let size=period*Math.max(1,pyRound(want/period));
+    while(size>hi) size-=period;
+    while(size<lo) size+=period;
+    return size;};
+  return [fit(px,wantW,DSL_MIN_W,DSL_MAX_W),fit(py,wantH,DSL_MIN_H,DSL_MAX_H)];
+}
+
+/** Run a program. Returns {w,h,scale,bits} in the same shape decodeOF gives. */
+function dslRender(raw){
+  const program=dslValidate(raw);
+  let [w,h]=dslSize(program);
+  const scale=Math.max(0,Math.min(7,program.canvas?.scale??1));
+  let buf=new Uint8Array(w*h);
+  for(const layer of program.layers){
+    const {fn}=DSL_SHAPES[layer.shape.type](layer.shape,[w,h]);
+    const op=layer.op;
+    for(let y=0;y<h;y++){const base=y*w;
+      for(let x=0;x<w;x++){
+        const v=fn(x,y),i=base+x;
+        if(op==='set') buf[i]=v;
+        else if(op==='union') buf[i]|=v;
+        else if(op==='intersect') buf[i]&=v;
+        else if(op==='xor') buf[i]^=v;
+        else if(op==='subtract') buf[i]&=1-v;}}}
+  const post=program.post||{};
+  const remap=(nw,nh,pick)=>{const out=new Uint8Array(nw*nh);
+    for(let y=0;y<nh;y++)for(let x=0;x<nw;x++) out[y*nw+x]=pick(x,y);
+    return out;};
+  if(post.mirrorX) buf=remap(w,h,(x,y)=>buf[y*w+(w-1-x)]);
+  if(post.mirrorY) buf=remap(w,h,(x,y)=>buf[(h-1-y)*w+x]);
+  for(let r=0;r<floorMod(post.rotate90||0,4);r++){
+    const src=buf,sw=w,sh=h;
+    buf=remap(sh,sw,(x,y)=>src[(sh-1-x)*sw+y]);
+    const t=w;w=h;h=t;}
+  if(post.invert) for(let i=0;i<buf.length;i++) buf[i]=1-buf[i];
+  return {w,h,scale,bits:buf};
+}
+
 // Flatten the visible layers to palette indices (top layer wins).
 function flatIndex(fi){
   const out=new Uint8Array(npx());
diff --git a/tests/fixtures/dsl.json b/tests/fixtures/dsl.json
new file mode 100644
index 0000000..83abd24
--- /dev/null
+++ b/tests/fixtures/dsl.json
@@ -0,0 +1,2430 @@
+{
+ "note": "Oracle for the parametric DSL. Rendered by tools/dsl_prototype.py, which tools/dsl_demo.py verifies tiles exactly. The editor's JavaScript must reproduce patternData byte for byte.",
+ "caseCount": 62,
+ "fonts": {
+  "5x7": {
+   "A": [
+    14,
+    17,
+    17,
+    31,
+    17,
+    17,
+    17
+   ],
+   "B": [
+    30,
+    17,
+    17,
+    30,
+    17,
+    17,
+    30
+   ],
+   "C": [
+    14,
+    17,
+    16,
+    16,
+    16,
+    17,
+    14
+   ],
+   "D": [
+    30,
+    17,
+    17,
+    17,
+    17,
+    17,
+    30
+   ],
+   "E": [
+    31,
+    16,
+    16,
+    30,
+    16,
+    16,
+    31
+   ],
+   "F": [
+    31,
+    16,
+    16,
+    30,
+    16,
+    16,
+    16
+   ],
+   "G": [
+    14,
+    17,
+    16,
+    23,
+    17,
+    17,
+    15
+   ],
+   "H": [
+    17,
+    17,
+    17,
+    31,
+    17,
+    17,
+    17
+   ],
+   "I": [
+    14,
+    4,
+    4,
+    4,
+    4,
+    4,
+    14
+   ],
+   "J": [
+    7,
+    2,
+    2,
+    2,
+    2,
+    18,
+    12
+   ],
+   "K": [
+    17,
+    18,
+    20,
+    24,
+    20,
+    18,
+    17
+   ],
+   "L": [
+    16,
+    16,
+    16,
+    16,
+    16,
+    16,
+    31
+   ],
+   "M": [
+    17,
+    27,
+    21,
+    21,
+    17,
+    17,
+    17
+   ],
+   "N": [
+    17,
+    25,
+    21,
+    19,
+    17,
+    17,
+    17
+   ],
+   "O": [
+    14,
+    17,
+    17,
+    17,
+    17,
+    17,
+    14
+   ],
+   "P": [
+    30,
+    17,
+    17,
+    30,
+    16,
+    16,
+    16
+   ],
+   "Q": [
+    14,
+    17,
+    17,
+    17,
+    21,
+    18,
+    13
+   ],
+   "R": [
+    30,
+    17,
+    17,
+    30,
+    20,
+    18,
+    17
+   ],
+   "S": [
+    15,
+    16,
+    16,
+    14,
+    1,
+    1,
+    30
+   ],
+   "T": [
+    31,
+    4,
+    4,
+    4,
+    4,
+    4,
+    4
+   ],
+   "U": [
+    17,
+    17,
+    17,
+    17,
+    17,
+    17,
+    14
+   ],
+   "V": [
+    17,
+    17,
+    17,
+    17,
+    17,
+    10,
+    4
+   ],
+   "W": [
+    17,
+    17,
+    17,
+    21,
+    21,
+    27,
+    17
+   ],
+   "X": [
+    17,
+    17,
+    10,
+    4,
+    10,
+    17,
+    17
+   ],
+   "Y": [
+    17,
+    17,
+    10,
+    4,
+    4,
+    4,
+    4
+   ],
+   "Z": [
+    31,
+    1,
+    2,
+    4,
+    8,
+    16,
+    31
+   ],
+   "0": [
+    14,
+    17,
+    19,
+    21,
+    25,
+    17,
+    14
+   ],
+   "1": [
+    4,
+    12,
+    4,
+    4,
+    4,
+    4,
+    14
+   ],
+   "2": [
+    14,
+    17,
+    1,
+    2,
+    4,
+    8,
+    31
+   ],
+   "3": [
+    31,
+    2,
+    4,
+    2,
+    1,
+    17,
+    14
+   ],
+   "4": [
+    2,
+    6,
+    10,
+    18,
+    31,
+    2,
+    2
+   ],
+   "5": [
+    31,
+    16,
+    30,
+    1,
+    1,
+    17,
+    14
+   ],
+   "6": [
+    6,
+    8,
+    16,
+    30,
+    17,
+    17,
+    14
+   ],
+   "7": [
+    31,
+    1,
+    2,
+    4,
+    8,
+    8,
+    8
+   ],
+   "8": [
+    14,
+    17,
+    17,
+    14,
+    17,
+    17,
+    14
+   ],
+   "9": [
+    14,
+    17,
+    17,
+    15,
+    1,
+    2,
+    12
+   ]
+  },
+  "3x5": {
+   "A": [
+    2,
+    5,
+    7,
+    5,
+    5
+   ],
+   "B": [
+    6,
+    5,
+    6,
+    5,
+    6
+   ],
+   "C": [
+    3,
+    4,
+    4,
+    4,
+    3
+   ],
+   "D": [
+    6,
+    5,
+    5,
+    5,
+    6
+   ],
+   "E": [
+    7,
+    4,
+    6,
+    4,
+    7
+   ],
+   "F": [
+    7,
+    4,
+    6,
+    4,
+    4
+   ],
+   "G": [
+    3,
+    4,
+    5,
+    5,
+    3
+   ],
+   "H": [
+    5,
+    5,
+    7,
+    5,
+    5
+   ],
+   "I": [
+    7,
+    2,
+    2,
+    2,
+    7
+   ],
+   "J": [
+    1,
+    1,
+    1,
+    5,
+    2
+   ],
+   "K": [
+    5,
+    5,
+    6,
+    5,
+    5
+   ],
+   "L": [
+    4,
+    4,
+    4,
+    4,
+    7
+   ],
+   "M": [
+    5,
+    7,
+    7,
+    5,
+    5
+   ],
+   "N": [
+    5,
+    7,
+    7,
+    7,
+    5
+   ],
+   "O": [
+    2,
+    5,
+    5,
+    5,
+    2
+   ],
+   "P": [
+    6,
+    5,
+    6,
+    4,
+    4
+   ],
+   "Q": [
+    2,
+    5,
+    5,
+    6,
+    3
+   ],
+   "R": [
+    6,
+    5,
+    6,
+    5,
+    5
+   ],
+   "S": [
+    3,
+    4,
+    2,
+    1,
+    6
+   ],
+   "T": [
+    7,
+    2,
+    2,
+    2,
+    2
+   ],
+   "U": [
+    5,
+    5,
+    5,
+    5,
+    7
+   ],
+   "V": [
+    5,
+    5,
+    5,
+    5,
+    2
+   ],
+   "W": [
+    5,
+    5,
+    7,
+    7,
+    5
+   ],
+   "X": [
+    5,
+    5,
+    2,
+    5,
+    5
+   ],
+   "Y": [
+    5,
+    5,
+    2,
+    2,
+    2
+   ],
+   "Z": [
+    7,
+    1,
+    2,
+    4,
+    7
+   ],
+   "0": [
+    7,
+    5,
+    5,
+    5,
+    7
+   ],
+   "1": [
+    2,
+    6,
+    2,
+    2,
+    7
+   ],
+   "2": [
+    6,
+    1,
+    2,
+    4,
+    7
+   ],
+   "3": [
+    6,
+    1,
+    2,
+    1,
+    6
+   ],
+   "4": [
+    5,
+    5,
+    7,
+    1,
+    1
+   ],
+   "5": [
+    7,
+    4,
+    6,
+    1,
+    6
+   ],
+   "6": [
+    3,
+    4,
+    7,
+    5,
+    7
+   ],
+   "7": [
+    7,
+    1,
+    2,
+    2,
+    2
+   ],
+   "8": [
+    7,
+    5,
+    7,
+    5,
+    7
+   ],
+   "9": [
+    7,
+    5,
+    7,
+    1,
+    6
+   ]
+  }
+ },
+ "cases": [
+  {
+   "name": "gallery:stripes_v",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "stripes",
+       "axis": "v",
+       "period": 8,
+       "thickness": 4
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 32,
+   "scale": 1,
+   "ink": 512,
+   "patternData": "APF4Dw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8PDw8"
+  },
+  {
+   "name": "gallery:stripes_h",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "stripes",
+       "axis": "h",
+       "period": 6,
+       "thickness": 3
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 30,
+   "scale": 1,
+   "ink": 480,
+   "patternData": "APFw________________AAAAAAAAAAAAAAAA________________AAAAAAAAAAAAAAAA________________AAAAAAAAAAAAAAAA________________AAAAAAAAAAAAAAAA________________AAAAAAAAAAAAAAAA"
+  },
+  {
+   "name": "gallery:diagonal",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "diagonal",
+       "dx": 1,
+       "dy": 1,
+       "period": 8,
+       "thickness": 5
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 32,
+   "scale": 1,
+   "ink": 640,
+   "patternData": "APF4Hx8fHz4-Pj58fHx8-Pj4-PHx8fHj4-Pjx8fHx4-Pj48fHx8fPj4-Pnx8fHz4-Pj48fHx8ePj4-PHx8fHj4-Pjx8fHx8-Pj4-fHx8fPj4-Pjx8fHx4-Pj48fHx8ePj4-PHx8fHz4-Pj58fHx8-Pj4-PHx8fHj4-Pjx8fHx4-Pj48"
+  },
+  {
+   "name": "gallery:diagonal_steep",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "diagonal",
+       "dx": 2,
+       "dy": 1,
+       "period": 8,
+       "thickness": 3
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 32,
+   "scale": 1,
+   "ink": 384,
+   "patternData": "APF4BwcHBxwcHBxwcHBwwcHBwQcHBwccHBwccHBwcMHBwcEHBwcHHBwcHHBwcHDBwcHBBwcHBxwcHBxwcHBwwcHBwQcHBwccHBwccHBwcMHBwcEHBwcHHBwcHHBwcHDBwcHBBwcHBxwcHBxwcHBwwcHBwQcHBwccHBwccHBwcMHBwcE"
+  },
+  {
+   "name": "gallery:checker",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "checker",
+       "cellW": 4,
+       "cellH": 4
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 32,
+   "scale": 1,
+   "ink": 512,
+   "patternData": "APF48PDw8PDw8PDw8PDw8PDw8A8PDw8PDw8PDw8PDw8PDw_w8PDw8PDw8PDw8PDw8PDwDw8PDw8PDw8PDw8PDw8PD_Dw8PDw8PDw8PDw8PDw8PAPDw8PDw8PDw8PDw8PDw8P8PDw8PDw8PDw8PDw8PDw8A8PDw8PDw8PDw8PDw8PDw8"
+  },
+  {
+   "name": "gallery:checker_tall",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "checker",
+       "cellW": 3,
+       "cellH": 5
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 30,
+   "height": 30,
+   "scale": 1,
+   "ink": 450,
+   "patternData": "AOFwOI7jOI7jOI7jOI7jOI7jOI7j-HEcx3Ecx3Ecx3Ecx3Ecx3Ecx4HjOI7jOI7jOI7jOI7jOI7jOI4fx3Ecx3Ecx3Ecx3Ecx3Ecx3EcOI7jOI7jOI7jOI7jOI7jOI7j-HEcx3Ecx3Ecx3Ecx3Ecx3EcxwE"
+  },
+  {
+   "name": "gallery:grid",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "grid",
+       "periodX": 8,
+       "periodY": 8,
+       "lineX": 1,
+       "lineY": 1
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 32,
+   "scale": 1,
+   "ink": 240,
+   "patternData": "APF4_____wEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQH_____AQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAf____8BAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEB_____wEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQEBAQE"
+  },
+  {
+   "name": "gallery:dots",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "dots",
+       "periodX": 8,
+       "periodY": 8,
+       "radius": 2
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 32,
+   "height": 32,
+   "scale": 1,
+   "ink": 208,
+   "patternData": "APF4AAAAAAAAAAAQEBAQODg4OHx8fHw4ODg4EBAQEAAAAAAAAAAAAAAAABAQEBA4ODg4fHx8fDg4ODgQEBAQAAAAAAAAAAAAAAAAEBAQEDg4ODh8fHx8ODg4OBAQEBAAAAAAAAAAAAAAAAAQEBAQODg4OHx8fHw4ODg4EBAQEAAAAAA"
+  },
+  {
+   "name": "gallery:dots_brick",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "dots",
+       "periodX": 8,
+       "periodY": 8,
+       "radius": 2,
+       "rowOffset": 4
+      }
+     }
+    ],
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+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "triangles",
+       "size": 5,
+       "orientation": "up"
+      }
+     }
+    ],
+    "post": {
+     "rotate90": 3
+    }
+   },
+   "width": 30,
+   "height": 30,
+   "scale": 1,
+   "ink": 540,
+   "patternData": "AOFwEEIIIcYYY8w555x77733_________--9995zzjnnGGOMMYQQQgghhBBijDHGnHPOuffee___________3nvvPeecc44xxhhDCCGEEEIIIcYYY8w555x77733_________--9995zzjnnGGOMMYQQQgg"
+  },
+  {
+   "name": "post_invert",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "triangles",
+       "size": 5,
+       "orientation": "up"
+      }
+     }
+    ],
+    "post": {
+     "invert": true
+    }
+   },
+   "width": 30,
+   "height": 30,
+   "scale": 1,
+   "ink": 360,
+   "patternData": "AOFwzz___OGHHz7wwAMHGGCAAAAAwPPPP3_44YcPPPDAAQYYIAAAAPD8888ffvjhAw88cIABBggAAAA8__zzhx9--MADDxxggAECAAAAzz___OGHHz7wwAMHGGCAAAAAwPPPP3_44YcPPPDAAQYYIAAAAAA"
+  },
+  {
+   "name": "post_rot90_invert",
+   "program": {
+    "canvas": {
+     "width": 32,
+     "height": 32,
+     "scale": 1,
+     "autoSize": true
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "triangles",
+       "size": 5,
+       "orientation": "up"
+      }
+     }
+    ],
+    "post": {
+     "rotate90": 1,
+     "invert": true
+    }
+   },
+   "width": 30,
+   "height": 30,
+   "scale": 1,
+   "ink": 360,
+   "patternData": "AOFw3nvvPeecc44xxhhDCCGEAAAAAAAAAAAhhBBijDHGnHPOuffee--9995zzjnnGGOMMYQQQggAAAAAAAAAEEIIIcYYY8w555x777333nvvPeecc44xxhhDCCGEAAAAAAAAAAAhhBBijDHGnHPOuffeew8"
+  },
+  {
+   "name": "canvas:fixed",
+   "program": {
+    "canvas": {
+     "width": 23,
+     "height": 17,
+     "scale": 3,
+     "autoSize": false
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "diagonal",
+       "dx": 1,
+       "dy": 1,
+       "period": 7,
+       "thickness": 3
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 23,
+   "height": 17,
+   "scale": 3,
+   "ink": 168,
+   "patternData": "AKs8h8Nhh8Mhh8MBh8MBh8MJh8MNh8MPh8MOh0MOhwMOhwMOhxMOhxsOhx8Ohx0OhxwOBw"
+  },
+  {
+   "name": "canvas:limits",
+   "program": {
+    "canvas": {
+     "width": 129,
+     "height": 65,
+     "scale": 0,
+     "autoSize": false
+    },
+    "layers": [
+     {
+      "op": "set",
+      "shape": {
+       "type": "checker",
+       "cellW": 1,
+       "cellH": 1
+      }
+     }
+    ],
+    "post": {}
+   },
+   "width": 129,
+   "height": 65,
+   "scale": 0,
+   "ink": 4192,
+   "patternData": "APj_qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqgA"
+  }
+ ]
+}
diff --git a/tools/gen-dsl-fixtures.py b/tools/gen-dsl-fixtures.py
new file mode 100644
index 0000000..9249c02
--- /dev/null
+++ b/tools/gen-dsl-fixtures.py
@@ -0,0 +1,188 @@
+#!/usr/bin/env python3
+"""
+Freeze the parametric DSL into a fixture the editor's JavaScript can be held to.
+
+WHY THIS EXISTS
+---------------
+`tools/dsl_prototype.py` is the reference implementation of the pattern DSL: 15
+primitives, each with a declared period, composed with set/union/intersect/xor/
+subtract, sized so the result tiles seamlessly by construction. `tools/dsl_demo.py`
+proves 28 programs tile exactly. Both have run on every commit since before the
+editor existed, and the editor has never used any of it.
+
+Porting it to JavaScript means two implementations that must agree forever. This
+turns the Python one into the oracle, the same way tests/fixtures/codec.json and
+tests/fixtures/sampler.json do for the codec and the sampler.
+
+WHAT IT COVERS
+--------------
+  * The 28 programs from dsl_demo's GALLERY — every primitive, plus the composite
+    examples docs/03 §4.6 and §4.7 promise.
+  * Each primitive again at non-default parameters, because a port that ignores
+    an argument still passes on defaults.
+  * Every composition op and every post transform, since those are where an
+    off-by-one in a mirror or a rotate hides.
+
+Determinism matters here: `noise` and `dots` jitter both go through the DSL's
+`_hash2`, which is written to be stable across languages. If the JavaScript hash
+disagrees by one bit, those cases diverge and this fixture says so.
+
+    python3 tools/gen-dsl-fixtures.py           # write + verify
+    python3 tools/gen-dsl-fixtures.py --check   # verify only, no write
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import sys
+
+HERE = os.path.dirname(os.path.abspath(__file__))
+sys.path.insert(0, HERE)
+ROOT = os.path.dirname(HERE)
+OUT = os.path.join(ROOT, "tests", "fixtures", "dsl.json")
+
+from dsl_prototype import (encode, render, tiles_exactly,     # noqa: E402
+                           FONT_5X7, FONT_3X5)
+from dsl_demo import GALLERY                                  # noqa: E402
+
+
+def prog(shape=None, canvas=None, layers=None, post=None) -> dict:
+    return {
+        "canvas": canvas or {"width": 32, "height": 32, "scale": 1, "autoSize": True},
+        "layers": layers or [{"op": "set", "shape": shape}],
+        "post": post or {},
+    }
+
+
+# Each primitive away from its defaults. A port that silently drops a parameter
+# renders the default and passes the gallery; it fails here.
+OFF_DEFAULTS = [
+    ("solid_only", {"type": "solid"}),
+    ("stripes_thin", {"type": "stripes", "axis": "h", "period": 7, "thickness": 2, "phase": 3}),
+    ("diagonal_steep", {"type": "diagonal", "dx": 3, "dy": 2, "period": 12, "thickness": 4, "phase": 5}),
+    ("checker_oblong", {"type": "checker", "cellW": 5, "cellH": 2, "phase": 1}),
+    ("grid_thick", {"type": "grid", "periodX": 9, "periodY": 6, "lineX": 3, "lineY": 2,
+                    "phaseX": 2, "phaseY": 4}),
+    ("dots_diamond", {"type": "dots", "periodX": 10, "periodY": 6, "radius": 3,
+                      "shape": "diamond", "rowOffset": 5}),
+    ("dots_square_jitter", {"type": "dots", "periodX": 8, "periodY": 8, "radius": 2,
+                            "shape": "square", "jitter": 2, "seed": 7}),
+    ("brick_offset", {"type": "brick", "brickW": 10, "brickH": 5, "mortar": 2, "offset": 3}),
+    ("wave_vertical", {"type": "wave", "axis": "v", "period": 14, "amplitude": 4, "thickness": 3,
+                       "phase": 2}),
+    ("zigzag_vertical", {"type": "zigzag", "axis": "v", "period": 10, "amplitude": 4, "thickness": 3}),
+    ("triangles_down", {"type": "triangles", "size": 6, "orientation": "down"}),
+    ("rings_offset", {"type": "rings", "period": 12, "thickness": 3, "cx": 4, "cy": 2}),
+    ("halftone_45", {"type": "halftone", "period": 10, "level": 0.8, "angle": 45}),
+    ("halftone_light", {"type": "halftone", "period": 6, "level": 0.15}),
+    ("noise_blue", {"type": "noise", "density": 0.35, "seed": 99, "blue": True}),
+    ("noise_plain", {"type": "noise", "density": 0.6, "seed": 12345}),
+    ("text_3x5", {"type": "text", "glyphs": "OF", "font": "3x5", "tracking": 2, "leading": 3}),
+    ("text_5x7", {"type": "text", "glyphs": "PF9", "font": "5x7", "tracking": 1, "leading": 1}),
+    ("border_inset", {"type": "border", "inset": 3, "thickness": 2}),
+]
+
+OPS = ["set", "union", "intersect", "xor", "subtract"]
+POSTS = [
+    ("post_mirrorX", {"mirrorX": True}),
+    ("post_mirrorY", {"mirrorY": True}),
+    ("post_both_mirrors", {"mirrorX": True, "mirrorY": True}),
+    ("post_rot90", {"rotate90": 1}),
+    ("post_rot180", {"rotate90": 2}),
+    ("post_rot270", {"rotate90": 3}),
+    ("post_invert", {"invert": True}),
+    ("post_rot90_invert", {"rotate90": 1, "invert": True}),
+]
+
+
+def cases() -> list[tuple[str, dict]]:
+    out: list[tuple[str, dict]] = []
+    for name, _desc, program in GALLERY:
+        out.append((f"gallery:{name}", program))
+    for name, shape in OFF_DEFAULTS:
+        out.append((f"params:{name}", prog(shape)))
+    # Composition: the same two shapes under every op, so an op that is wired to
+    # the wrong bitwise operator cannot hide behind a shape that rarely overlaps.
+    for op in OPS:
+        out.append((f"op:{op}", prog(None, layers=[
+            {"op": "set", "shape": {"type": "stripes", "axis": "v", "period": 8, "thickness": 5}},
+            {"op": op, "shape": {"type": "stripes", "axis": "h", "period": 6, "thickness": 4}},
+        ])))
+    # Asymmetric source, so a mirror or rotate that is a no-op is visible.
+    asym = {"type": "triangles", "size": 5, "orientation": "up"}
+    for name, post in POSTS:
+        out.append((f"{name}", prog(asym, post=post)))
+    # Explicit sizing, where the tiling guarantee is deliberately switched off.
+    out.append(("canvas:fixed", prog(
+        {"type": "diagonal", "dx": 1, "dy": 1, "period": 7, "thickness": 3},
+        canvas={"width": 23, "height": 17, "scale": 3, "autoSize": False})))
+    out.append(("canvas:limits", prog(
+        {"type": "checker", "cellW": 1, "cellH": 1},
+        canvas={"width": 129, "height": 65, "scale": 0, "autoSize": False})))
+    return out
+
+
+def main() -> int:
+    check_only = "--check" in sys.argv
+    built = []
+    tiling_failures = []
+
+    for name, program in cases():
+        w, h, scale, buf = render(program)
+        data = encode(w, h, scale, buf)
+        ok, _px, _py = tiles_exactly(program, w, h)
+        if program.get("canvas", {}).get("autoSize", True) and not ok:
+            tiling_failures.append(name)
+        built.append({
+            "name": name,
+            "program": program,
+            "width": w,
+            "height": h,
+            "scale": scale,
+            "ink": sum(buf),
+            "patternData": data,
+        })
+
+    if tiling_failures:
+        print("*** programs with autoSize that do not tile exactly: "
+              f"{', '.join(tiling_failures)} ***")
+        return 1
+
+    doc = {
+        "note": ("Oracle for the parametric DSL. Rendered by tools/dsl_prototype.py, "
+                 "which tools/dsl_demo.py verifies tiles exactly. The editor's "
+                 "JavaScript must reproduce patternData byte for byte."),
+        "caseCount": len(built),
+        # The glyph tables the editor carries a copy of. Transcribing these by
+        # hand once put a wrong 'D' in the 5x7 font and rewrote half of 3x5; the
+        # text cases caught it, but as "384 lit pixels, oracle says 400", which
+        # names the symptom rather than the cause. Comparing the tables directly
+        # says which glyph.
+        "fonts": {"5x7": FONT_5X7, "3x5": FONT_3X5},
+        "cases": built,
+    }
+
+    if check_only:
+        if not os.path.exists(OUT):
+            print(f"{OUT} is missing — run without --check")
+            return 1
+        if json.load(open(OUT, encoding="utf-8")) != doc:
+            print(f"{OUT} is stale — re-run without --check")
+            return 1
+        print(f"DSL fixtures current  {len(built)} programs, all autoSize cases tile exactly")
+        return 0
+
+    os.makedirs(os.path.dirname(OUT), exist_ok=True)
+    with open(OUT, "w", encoding="utf-8") as fh:
+        json.dump(doc, fh, indent=1)
+        fh.write("\n")
+    shapes = {c["program"]["layers"][0]["shape"]["type"] for c in built}
+    print(f"wrote {OUT}")
+    print(f"  {len(built)} programs  {len(shapes)} distinct primitives in the first layer")
+    print(f"  every autoSize program tiles exactly")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/tools/verify-all.sh b/tools/verify-all.sh
index a4641e6..716d290 100755
--- a/tools/verify-all.sh
+++ b/tools/verify-all.sh
@@ -38,6 +38,8 @@ run "codec corpus"                 python3 tools/gen-codec-fixtures.py --check
 run "editor codec vs corpus"       node    tools/verify-codec.js
 run "sampler oracle"               python3 tools/gen-sampler-fixtures.py --check
 run "editor sampler vs oracle"     node    tools/verify-sampler.js
+run "DSL oracle"                   python3 tools/gen-dsl-fixtures.py --check
+run "editor DSL vs oracle"         node    tools/verify-dsl.js
 run "DSL prototype + seam metric"  python3 tools/dsl_demo.py
 run "router prompt examples"       python3 tools/verify-prompt.py
 run "map-scale sampling"           python3 tools/preview_prototype.py
diff --git a/tools/verify-dsl.js b/tools/verify-dsl.js
new file mode 100644
index 0000000..c233627
--- /dev/null
+++ b/tools/verify-dsl.js
@@ -0,0 +1,142 @@
+#!/usr/bin/env node
+/*
+ * Run the EDITOR'S OWN DSL against the Python oracle.
+ *
+ * tools/dsl_prototype.py is the reference implementation and tools/dsl_demo.py
+ * proves 28 programs tile exactly. Neither says anything about the JavaScript a
+ * user's pattern actually goes through. This lifts the real renderer out of
+ * app/patternfront.html and re-renders every program in tests/fixtures/dsl.json,
+ * comparing the encoded result byte for byte.
+ *
+ * Byte-for-byte is the right bar rather than "looks similar": four things in the
+ * Python do not survive a literal translation, and each fails silently.
+ *
+ *   round()   banker's rounding, so round(2.5) is 2 where Math.round gives 3.
+ *             It decides wave offsets and canvas sizing.
+ *   %         a floor modulo in Python, a remainder in JS. Any expression that
+ *             can go negative diverges.
+ *   //        floors, where |0 truncates toward zero.
+ *   _hash2    multiplies by constants near 2^31; a plain * passes 2^53 and drops
+ *             low bits, so noise and dot jitter drift apart.
+ *
+ * A pattern that is one pixel different still encodes to a different string, so
+ * any of those shows up here as a mismatch rather than as a subtly wrong export.
+ *
+ *   node tools/verify-dsl.js
+ */
+
+'use strict';
+const fs = require('fs');
+const path = require('path');
+const vm = require('vm');
+const { editorJs, grabFunction, grabConst } = require('./lib/extract');
+
+const ROOT = path.join(__dirname, '..');
+const FIXTURES = path.join(ROOT, 'tests', 'fixtures', 'dsl.json');
+
+if (!fs.existsSync(FIXTURES)) {
+  console.log(`missing ${FIXTURES}`);
+  console.log('run: python3 tools/gen-dsl-fixtures.py');
+  process.exit(2);
+}
+
+const js = editorJs();
+const ctx = {
+  Uint8Array, Error, Math, JSON, Object, String, Array,
+  btoa: s => Buffer.from(s, 'binary').toString('base64'),
+};
+vm.createContext(ctx);
+vm.runInContext([
+  grabConst(js, 'floorMod'),
+  grabFunction(js, 'encodeOF'),
+  grabFunction(js, 'pyRound'),
+  grabFunction(js, 'gcd'),
+  grabFunction(js, 'lcm'),
+  grabFunction(js, 'hash2'),
+  grabConst(js, 'F57'),
+  grabConst(js, 'F35'),
+  grabConst(js, 'DSL_MIN_W'),
+  grabMulti('DSL_SHAPES'),
+  grabConst(js, 'DSL_CANVAS_LOCKED'),
+  grabMulti('DSL_RANGES'),
+  grabFunction(js, 'dslValidateShape'),
+  grabFunction(js, 'dslValidate'),
+  grabFunction(js, 'dslSize'),
+  grabFunction(js, 'dslRender'),
+].join('\n'), ctx);
+
+/** A multi-line `const NAME={...};` — grabConst only handles single lines. */
+function grabMulti(name) {
+  const at = js.indexOf(`const ${name}=`);
+  if (at < 0) throw new Error(`const ${name} not found in the editor`);
+  const { matchBrace } = require('./lib/extract');
+  const open = js.indexOf('{', at);
+  return js.slice(at, matchBrace(js, open) + 1) + ';';
+}
+
+const dslRender = vm.runInContext('dslRender', ctx);
+const encodeOF = vm.runInContext('encodeOF', ctx);
+const pyRound = vm.runInContext('pyRound', ctx);
+
+const corpus = JSON.parse(fs.readFileSync(FIXTURES, 'utf8'));
+const failures = [];
+
+// State the rounding rule as a check, rather than leaving the fixture to imply
+// it. If this is wrong, several cases below fail for a reason nobody would guess.
+for (const [input, want] of [[0.5, 0], [1.5, 2], [2.5, 2], [3.5, 4], [-2.5, -2], [2.4, 2]]) {
+  if (pyRound(input) !== want) {
+    failures.push(`pyRound(${input}) is ${pyRound(input)}, Python gives ${want}`);
+  }
+}
+
+// Compare the glyph tables directly. The editor keeps its own copy, and a bad
+// transcription otherwise surfaces only as a lit-pixel count being off.
+{
+  const F57 = vm.runInContext('F57', ctx), F35 = vm.runInContext('F35', ctx);
+  for (const [label, want, got] of [['5x7', corpus.fonts['5x7'], F57],
+                                    ['3x5', corpus.fonts['3x5'], F35]]) {
+    const wrong = Object.keys(want)
+      .filter(k => JSON.stringify(want[k]) !== JSON.stringify(got[k]));
+    if (wrong.length) {
+      failures.push(`${label} font: ${wrong.length}/${Object.keys(want).length} `
+                  + `glyphs differ from the source table (${wrong.slice(0, 8).join(' ')})`);
+    }
+  }
+}
+
+const primitives = new Set();
+for (const c of corpus.cases) {
+  let got;
+  try { got = dslRender(c.program); }
+  catch (e) { failures.push(`${c.name}: dslRender threw ${e.message}`); continue; }
+
+  if (got.w !== c.width || got.h !== c.height) {
+    failures.push(`${c.name}: sized ${got.w}x${got.h}, oracle says ${c.width}x${c.height}`);
+    continue;
+  }
+  const ink = got.bits.reduce((a, b) => a + b, 0);
+  if (ink !== c.ink) {
+    failures.push(`${c.name}: ${ink} lit pixels, oracle says ${c.ink}`);
+    continue;
+  }
+  const data = encodeOF(got.w, got.h, got.scale, got.bits);
+  if (data !== c.patternData) {
+    failures.push(`${c.name}: encodes to a different pattern `
+                + `(${data.length} vs ${c.patternData.length} chars)`);
+    continue;
+  }
+  for (const l of c.program.layers) primitives.add(l.shape.type);
+}
+
+console.log(`${corpus.cases.length} programs through the editor's own DSL`);
+console.log(`  ${primitives.size} primitives exercised, `
+          + `every result compared as encoded patternData`);
+
+if (failures.length) {
+  console.log(`\n*** ${failures.length} FAILURE(S) ***`);
+  for (const f of failures.slice(0, 20)) console.log(`    - ${f}`);
+  if (failures.length > 20) console.log(`    ... and ${failures.length - 20} more`);
+  process.exit(1);
+}
+console.log('  the shipping renderer agrees with the oracle byte for byte');
+console.log('ALL DSL CHECKS PASSED');