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README.md

@@ -8,8 +8,64 @@ pinned: false
 license: mit
 ---
 
+# Slapstack Studio — Bet 9 (splat eraser · backdrop · band gains)
+
+Bet 8 plus the editing layer: this is the "adaptive density control by hand"
+step — delete splats, clean images, control the look. **Client-only delta**:
+`app.py`, `oracle.py`, and the verified BP core are byte-identical to Bet 8, so
+deploying is replacing `studio_ui.html`, `studio_core.js`, and the built
+`studio/studio.html` on the existing Space (or pushing this repo as-is).
+
+## New in Bet 9 — all in the EDIT & LOOK card
+
+**Erase tool.** Switch tool from *pose* to *erase*; three brush sizes (S/M/L);
+drag over the canvas and atoms under the brush are deleted. Works in soup and
+bound states. Mechanically an erase filters every per-atom parallel array
+(obs, gt, evidence, assignment, marginals) by the brush mask — atom order
+carries no meaning anywhere in the system (additive render, per-atom
+marginals), so **Undo** is simply re-appending the removed records, and the
+field restores bit-exactly (verified). Undo history survives until the next
+Bind/Scramble (BP re-inference makes the records stale, so the stack clears —
+honestly, rather than pretending).
+
+**Burn into template.** By default erases are scene-level: Scramble rebuilds
+from the layer templates and the splats come back. Tick *burn into template*
+and each erased atom is also removed from its source layer's template (tracked
+by reference through the scene build), so the cleanup is permanent — the
+hand-operated version of 3DGS adaptive density pruning. Undo restores burned
+atoms too.
+
+**Backdrop.** A color picker and an image upload. The backdrop is pure
+presentation state, touched by nothing in the inference loop — which is
+exactly why it *persists* across Bind/Scramble/drag instead of reverting to
+gray. The gray you see by default is not a background at all: it is
+sigmoid(0), the neutral of the additive field where no atom paints. The
+backdrop composites under the field using the rendered-deviation alpha
+(`alphaFromPre`), so cancelling atom pairs stay transparent over your image.
+
+**Gains.** The dials from the original splatstack direct-fit editor, back:
+coarse (<4 c/img), mid (4–10), fine (>10) band gains plus a global opacity
+gain. Render-only, like before — occlusion evidence and BP are untouched.
+Exactness for free: the Gabor render is linear in atom color, so
+Σ_b gain_b·render(band_b) ≡ render(gain-scaled atoms), verified to 2.4e-7.
+Band gains apply in field mode; opacity applies in both modes.
+
+**Ledger for this drop.** `tests_edit.js`: 13/13 GO (band edges, gain
+linearity, backdrop identities incl. the image path, brush geometry + veto,
+erase→undo bit-exact round trip, burn/unburn template membership).
+`tests_studio.js` regression: unchanged from shipped Bet 8 (11 GO and the one
+known inherited coverage-overlap FAIL, untouched by this delta). All four
+script blocks of the built `studio/studio.html` (106 KB) syntax-verified.
+Untouched and still honestly unverified: the GPU SDS path.
+
+---
+
 # Slapstack Studio (Bet 8 Playroom)
 
+Live at huggingface: https://huggingface.co/spaces/Aluode/SlapStackStudio
+
+Video: [https://studio.youtube.com/video/a-emh7csWQk/edit](https://youtu.be/a-emh7csWQk)
+
 ![pic2](pic2.png)
 
 An interactive, layered visual sandbox running multi-object Belief Propagation (BP) over Gabor packet representations. The system supports full 2D depth occlusion matting, spatial grab/drag/scale/rotate mechanics, semantic prompt interventions, and server-side neural layer distillation via Score Distillation Sampling (SDS).
@@ -90,8 +146,3 @@ Open your browser and navigate to http://127.0.0.1:7860. The unified workspace w
 ### Prompt Interventions
 
 Enter clean, natural commands in the prompt box (e.g., *"move the boat left, send the star behind the tractor"*) to execute hard algebraic transformations. The graph instantly recalculates the new joint posterior distribution around your action.
-
-Future direction: 
-
-Deleting splats to seperate background fuzz from the images would fit here great. I think there has been a lot of work on 3d splats on this. So I guess the work is already done?
-

requirements.txt

@@ -1,4 +1,4 @@
-gradio<6.0
+gradio
 diffusers
 transformers
 torch

studio/studio.html

@@ -72,6 +72,11 @@ button.primary{border-color:var(--phosphor);color:var(--phosphor)}
 label.tog{display:flex;gap:8px;align-items:center;cursor:pointer;padding:2px 0;font-size:12px}
 label.tog input{accent-color:var(--phosphor)}
 input[type=range]{flex:1;accent-color:var(--phosphor)}
+.gain-row{display:grid;grid-template-columns:54px 1fr 40px;gap:6px;align-items:center;margin-top:3px}
+.gain-row input[type=range]{width:100%;margin:0}
+.gain-row .val{text-align:right}
+input[type=color]{width:36px;height:22px;padding:1px;border:1px solid var(--panel-edge);background:var(--well);border-radius:4px;cursor:pointer}
+#stage.erasing #overlay-canvas{cursor:crosshair}
 input[type=text],textarea{font-family:var(--mono);font-size:12px;background:var(--well);
   color:var(--ink);border:1px solid var(--panel-edge);border-radius:4px;padding:6px 8px;width:100%}
 input[type=text]:focus-visible,textarea:focus-visible{outline:2px solid var(--phosphor);border-color:transparent}
@@ -99,7 +104,7 @@ input[type=file]{font-size:10.5px;color:var(--muted);max-width:170px}
     <div id="stage">
       <canvas id="scene-canvas"></canvas>
       <canvas id="overlay-canvas"></canvas>
-      <div class="hint">drag = pose clamp &middot; wheel rotate &middot; shift+wheel scale &middot; shift+click = semantic hint for selected layer</div>
+      <div class="hint">drag = pose clamp &middot; wheel rotate &middot; shift+wheel scale &middot; shift+click = hint &middot; erase tool: brush deletes atoms</div>
     </div>
   </div>
 
@@ -129,6 +134,36 @@ input[type=file]{font-size:10.5px;color:var(--muted);max-width:170px}
       </div>
     </div>
 
+    <div class="card">
+      <h2>EDIT &amp; LOOK</h2>
+      <div class="row">
+        <span class="dim">tool</span>
+        <label class="tog"><input type="radio" name="tool" value="pose" checked> pose</label>
+        <label class="tog"><input type="radio" name="tool" value="erase"> erase</label>
+        <span class="spacer"></span>
+        <span class="dim">brush</span>
+        <label class="tog"><input type="radio" name="brush" value="0.05"> S</label>
+        <label class="tog"><input type="radio" name="brush" value="0.12" checked> M</label>
+        <label class="tog"><input type="radio" name="brush" value="0.25"> L</label>
+      </div>
+      <div class="row">
+        <button id="btn-undo-erase" disabled>Undo erase</button>
+        <button id="btn-restore-erase" disabled>Restore all</button>
+        <label class="tog"><input type="checkbox" id="erase-burn"> burn into template</label>
+      </div>
+      <div class="row">
+        <span class="dim">backdrop</span>
+        <input type="color" id="bg-color" value="#808080" title="backdrop color">
+        <input type="file" id="bg-file" accept="image/*" style="max-width:46%">
+        <button id="btn-bg-clear">clear img</button>
+      </div>
+      <div class="gain-row"><span class="dim">coarse</span><input type="range" id="g-coarse" min="0" max="200" value="100"><span class="val readout" id="g-coarse-v">1.00</span></div>
+      <div class="gain-row"><span class="dim">mid</span><input type="range" id="g-mid" min="0" max="200" value="100"><span class="val readout" id="g-mid-v">1.00</span></div>
+      <div class="gain-row"><span class="dim">fine</span><input type="range" id="g-fine" min="0" max="200" value="100"><span class="val readout" id="g-fine-v">1.00</span></div>
+      <div class="gain-row"><span class="dim">opacity</span><input type="range" id="g-op" min="0" max="200" value="100"><span class="val readout" id="g-op-v">1.00</span></div>
+      <div class="dim" style="font-size:10.5px;margin-top:6px">Erase deletes atoms under the brush (render only, until <b>burn</b> writes it into the layer template; Scramble/Bind rebuild the scene from templates). Undo works until the next Bind. Backdrop is presentation and survives everything. Band gains (coarse&lt;4, mid 4&ndash;10, fine&gt;10&nbsp;c/img) scale atom colors in field mode; opacity blends the whole field over the backdrop.</div>
+    </div>
+
     <div class="card">
       <h2>LAYERS <span class="dim" style="letter-spacing:0">(front is highest)</span></h2>
       <div id="layer-list"></div>
@@ -177,7 +212,7 @@ input[type=file]{font-size:10.5px;color:var(--muted);max-width:170px}
     <div class="card" id="ledger">
       <details>
         <summary>HONEST LEDGER</summary>
-        <p><b>Verified in this build:</b> the BP core matches the SlapstackBet6 Python (transform 2e-16, render MSE 8.6e-8, identical binding); drag = pose clamp + re-settle; identity persists through occlusion; depth occlusion removes evidence honestly (marginals revert toward the prior, coverage releases when moved away); the semantic likelihood factor resolves the twins case (two identical stars: 0.05 acc on geometry alone, 0.99 with location priors) and a mildly wrong prior is overridden by evidence; image&rarr;layer fitting runs end to end on CPU.</p>
+        <p><b>Verified in this build:</b> the BP core matches the SlapstackBet6 Python (transform 2e-16, render MSE 8.6e-8, identical binding); drag = pose clamp + re-settle; identity persists through occlusion; depth occlusion removes evidence honestly (marginals revert toward the prior, coverage releases when moved away); the semantic likelihood factor resolves the twins case (two identical stars: 0.05 acc on geometry alone, 0.99 with location priors) and a mildly wrong prior is overridden by evidence; image&rarr;layer fitting runs end to end on CPU. <b>Bet 9:</b> the eraser filters per-atom state (order-free, so undo is re-append), burn edits the template so erases survive rebuilds; the backdrop is pure presentation and persists across Bind/Scramble; band gains exploit render linearity (gain&middot;color &equiv; gain&middot;contribution), verified in tests_edit.js.</p>
         <p><span class="no">Not verified:</span> text&rarr;layer (SDS) and cross-attention matte are line-for-line adaptations of the verified Bet-5 GPU loop but have NOT been executed on a GPU — first run is a smoke test; SD attention maps flicker across seeds, which is why they enter BP as a prior with a weight, never as truth. Real-photo scene&rarr;atoms remains open. Painter compositing and the alpha matte are presentation choices, not the additive field model.</p>
       </details>
     </div>
@@ -702,6 +737,47 @@ function trimAtoms(atoms, sigMax = 0.35) {
   return kept.map(a => { const b = a.slice(); b[0] -= mx; b[1] -= my; return b; });
 }
 
+/* ---- Bet 9 additions: eraser + backdrop + band gains (pure, testable) ---- */
+
+/* Frequency band of an atom. f is cycles/unit; the frame spans 2 units, so
+   cycles-per-image = 2f. Bands follow the original splatstack dials:
+   coarse < 4 c/img, mid 4–10, fine > 10.  Returns 0|1|2. */
+const BAND_EDGES = [2.0, 5.0];
+function bandOf(f) { return f < BAND_EDGES[0] ? 0 : f < BAND_EDGES[1] ? 1 : 2; }
+
+/* Erase mask: true for atoms whose center falls inside the brush circle.
+   skip(i) can veto (e.g. atoms of hidden layers stay untouched). */
+function eraseMask(obs, wx, wy, r, skip) {
+  const r2 = r * r;
+  return obs.map((a, i) => {
+    if (skip && skip(i)) return false;
+    const dx = a[0] - wx, dy = a[1] - wy;
+    return dx * dx + dy * dy < r2;
+  });
+}
+
+/* Composite an already-sigmoided field over a backdrop.
+   img: Uint8ClampedArray RGBA from sigmoidField/compositePainter (mutated).
+   alpha: Float32Array(H*H) from alphaFromPre of the (band-gained) pre field.
+   opacity: global gain on alpha, clamped to [0,1] per pixel.
+   bg: either [r,g,b] flat color or a Uint8ClampedArray(4*H*H) RGBA image.
+   Identity check: with alpha==1 everywhere or bg==the field itself the
+   output is unchanged; with opacity such that a==1 the field wins. */
+function blendOverBackdrop(img, alpha, opacity, bg, H) {
+  const n = H * H;
+  const flat = !(bg && bg.length === 4 * n);
+  for (let i = 0; i < n; i++) {
+    const a = Math.min(1, alpha[i] * opacity);
+    const br = flat ? bg[0] : bg[4 * i],
+          bgr = flat ? bg[1] : bg[4 * i + 1],
+          bb = flat ? bg[2] : bg[4 * i + 2];
+    img[4 * i]     = br  + a * (img[4 * i]     - br);
+    img[4 * i + 1] = bgr + a * (img[4 * i + 1] - bgr);
+    img[4 * i + 2] = bb  + a * (img[4 * i + 2] - bb);
+  }
+  return img;
+}
+
 /* Sim(2) composition in vote coordinates: (g2 ∘ g1). */
 function composePose(g2, g1) {
   const s2 = Math.exp(g2[3]);
@@ -754,6 +830,19 @@ const S = {
 };
 let nextDepth = 1, nextId = 1;
 
+/* ---- Bet 9: eraser / backdrop / band-gain state ---- */
+const GAINS = { band: [1, 1, 1], opacity: 1 };
+const backdrop = { custom: false, rgb: [128, 128, 128], img: null }; // img: RGBA RES*RES
+let bandPre = null, bandDirty = true;
+const fieldAlpha = new Float32Array(RES * RES);
+let eraseStack = [], lastCursor = null;
+function toolMode(){ return document.querySelector('input[name=tool]:checked').value; }
+function brushR(){ return +document.querySelector('input[name=brush]:checked').value; }
+function updateEraseButtons(){
+  document.getElementById("btn-undo-erase").disabled = !eraseStack.length;
+  document.getElementById("btn-restore-erase").disabled = !eraseStack.length;
+}
+
 function addLayer(name, template, autoPlace) {
   const [color, rgb] = PALETTE[(S.layers.length) % PALETTE.length];
   const L = { id: nextId++, name, color, rgb, template, placed: false,
@@ -782,17 +871,19 @@ function rand(){ rngState=(rngState*1103515245+12345)&0x7fffffff; return rngStat
 function rebuildScene() {
   S.placed = S.layers.map((L,i)=>L.placed?i:-1).filter(i=>i>=0);
   const noiseAmt = 0.006 * Math.pow(3, +document.getElementById("noise").value / 3);
-  S.obs = []; S.gt = [];
+  S.obs = []; S.gt = []; S.src = [];
   S.placed.forEach((li,k)=>{
-    for (const a of transformAtoms(S.layers[li].template, S.layers[li].pose)) {
-      S.obs.push(a); S.gt.push(k);
+    const tmpl = S.layers[li].template;
+    const tr = transformAtoms(tmpl, S.layers[li].pose);
+    for (let j = 0; j < tr.length; j++) {
+      S.obs.push(tr[j]); S.gt.push(k); S.src.push({ li, ref: tmpl[j] });
     }
   });
   for (let i=0;i<12;i++){
     const su=0.04+0.08*rand();
     S.obs.push([-0.95+1.9*rand(),-0.95+1.9*rand(),-Math.PI/2+Math.PI*rand(),
       su,su*(0.4+0.5*rand()),4+10*rand(),TAU*rand(),rand(),rand(),rand()]);
-    S.gt.push(-1);
+    S.gt.push(-1); S.src.push(null);
   }
   for (const a of S.obs) for(let q=0;q<10;q++){
     const g=Math.sqrt(-2*Math.log(rand()+1e-9))*Math.cos(TAU*rand());
@@ -804,6 +895,7 @@ function rebuildScene() {
   S.covFrac=S.placed.map(()=>0);
   S.coastT=S.placed.map(()=>0);
   S.ownField=null;
+  eraseStack=[]; updateEraseButtons();
   setPhase("soup");
   rebuildGroupBuffers();
   renderScene(); drawOverlay(); renderLayerList(); renderLibrary(); updatePanels();
@@ -861,12 +953,28 @@ function rebuildGroupBuffers(){
     renderPre([S.obs[i]],RES,S.groupPre[g]);
   }
   for(let g=0;g<=K;g++) S.groupAlpha.push(alphaFromPre(S.groupPre[g],RES));
+  bandDirty=true;
 }
 function rebuildOneGroup(k){
   S.groupPre[k]=new Float32Array(3*RES*RES);
   if(!S.layers[S.placed[k]].hidden)
     renderPre(groupAtomIdx(k).map(i=>S.obs[i]),RES,S.groupPre[k]);
   S.groupAlpha[k]=alphaFromPre(S.groupPre[k],RES);
+  bandDirty=true;
+}
+/* frequency-band buffers, built lazily only when a band gain != 1.
+   Same visibility rule as the group buffers; render is linear in atom color,
+   so gain*color == gain*contribution and Σ_b gain_b·bandPre_b is exact. */
+function rebuildBandBuffers(){
+  const K=S.placed.length;
+  bandPre=[new Float32Array(3*RES*RES),new Float32Array(3*RES*RES),new Float32Array(3*RES*RES)];
+  const groupOf=i=>{ const g=S.marg?believedGroup(i):S.gt[i]; return g>=0?g:K; };
+  for(let i=0;i<S.obs.length;i++){
+    const g=groupOf(i);
+    if(g<K && S.layers[S.placed[g]].hidden) continue;
+    renderPre([S.obs[i]],RES,bandPre[bandOf(S.obs[i][5])]);
+  }
+  bandDirty=false;
 }
 const sceneCtx=sceneC.getContext("2d");
 const compositePre=new Float32Array(3*RES*RES);
@@ -874,16 +982,40 @@ const sceneImg=new ImageData(RES,RES);
 function compMode(){ return document.querySelector('input[name=comp]:checked').value; }
 function renderScene(){
   const K=S.placed.length;
+  const gb=GAINS.band, gainsOn=gb[0]!==1||gb[1]!==1||gb[2]!==1;
+  const bgOn=backdrop.custom||backdrop.img||GAINS.opacity!==1;
   if(compMode()==="field"){
     compositePre.fill(0);
-    for(const buf of S.groupPre)
-      for(let i=0;i<compositePre.length;i++) compositePre[i]+=buf[i];
+    if(gainsOn){
+      if(bandDirty) rebuildBandBuffers();
+      for(let b=0;b<3;b++){
+        const g=gb[b]; if(!g) continue;
+        const buf=bandPre[b];
+        for(let i=0;i<compositePre.length;i++) compositePre[i]+=g*buf[i];
+      }
+    } else {
+      for(const buf of S.groupPre)
+        for(let i=0;i<compositePre.length;i++) compositePre[i]+=buf[i];
+    }
     sigmoidField(compositePre,RES,sceneImg.data);
+    if(bgOn){
+      alphaFromPre(compositePre,RES,fieldAlpha);
+      blendOverBackdrop(sceneImg.data,fieldAlpha,GAINS.opacity,backdrop.img||backdrop.rgb,RES);
+    }
   } else {
     // painter: clutter at the back, then placed layers by depth
     const order=[K, ...S.placed.map((li,k)=>k)
       .sort((a,b)=>S.layers[S.placed[a]].depth-S.layers[S.placed[b]].depth)];
     compositePainter(order,S.groupPre,S.groupAlpha,RES,sceneImg.data);
+    if(bgOn){
+      // union alpha of everything rendered (band gains are field-mode only)
+      for(let i=0;i<RES*RES;i++){
+        let keep=1;
+        for(let q=0;q<=K;q++) keep*=1-S.groupAlpha[q][i];
+        fieldAlpha[i]=1-keep;
+      }
+      blendOverBackdrop(sceneImg.data,fieldAlpha,GAINS.opacity,backdrop.img||backdrop.rgb,RES);
+    }
   }
   sceneCtx.putImageData(sceneImg,0,0);
 }
@@ -993,6 +1125,14 @@ function drawOverlay(){
       }
     }
   }
+
+  if(toolMode()==="erase"&&lastCursor){       // eraser brush cursor
+    ctx.strokeStyle="rgba(255,120,110,0.9)";
+    ctx.lineWidth=1.4*px1;ctx.setLineDash([4*px1,3*px1]);
+    ctx.beginPath();
+    ctx.arc(w2p(lastCursor[0]),w2p(lastCursor[1]),brushR()*overC.width/2,0,TAU);
+    ctx.stroke();ctx.setLineDash([]);
+  }
 }
 
 /* ------------- semantic factor from hints ------------- */
@@ -1049,6 +1189,7 @@ function runBind(opts={}){
 function bind(animate=true){
   if(S.phase==="binding"||!S.placed.length) return;
   S.assign=null;
+  eraseStack=[]; updateEraseButtons();   // erase history is stale once BP re-runs
   S.evid=S.obs.map(()=>true);      // full re-bind: everything is evidence again
   for(const li of S.placed) if(S.layers[li].hidden){
     // user-hidden layers stay evidence-free
@@ -1132,6 +1273,70 @@ function applyGesture(k,g){
   renderScene();drawOverlay();updatePanels();
 }
 
+/* ------------- eraser (Bet 9) -------------
+   Deleting an atom = filtering every per-atom parallel array by the brush
+   mask. Order of atoms carries no meaning anywhere (additive render, per-atom
+   marginals), so undo can simply re-append the removed records.
+   Undo is valid until the next Bind/Scramble/place/remove (those rebuild or
+   re-infer the per-atom state). "Burn" additionally removes the source atom
+   from the layer TEMPLATE, so the erase survives scene rebuilds. */
+function eraseAt(wx,wy,stroke){
+  const skip=i=>{ const g=believedGroup(i); return g>=0&&S.layers[S.placed[g]].hidden; };
+  const mask=eraseMask(S.obs,wx,wy,brushR(),skip);
+  let any=false; for(const m of mask) if(m){any=true;break;}
+  if(!any) return;
+  const kObs=[],kGt=[],kSrc=[],kEvid=[],
+        kAssign=S.assign?[]:null, kMarg=S.marg?[]:null;
+  for(let i=0;i<S.obs.length;i++){
+    if(mask[i]){
+      stroke.atoms.push({a:S.obs[i],gt:S.gt[i],src:S.src[i],evid:S.evid[i],
+        assign:S.assign?S.assign[i]:null, marg:S.marg?S.marg[i]:null});
+    } else {
+      kObs.push(S.obs[i]);kGt.push(S.gt[i]);kSrc.push(S.src[i]);kEvid.push(S.evid[i]);
+      if(kAssign)kAssign.push(S.assign[i]);
+      if(kMarg)kMarg.push(S.marg[i]);
+    }
+  }
+  S.obs=kObs;S.gt=kGt;S.src=kSrc;S.evid=kEvid;
+  if(kAssign)S.assign=kAssign;
+  if(kMarg)S.marg=kMarg;
+  rebuildGroupBuffers();renderScene();drawOverlay();updatePanels();
+}
+function commitStroke(stroke){
+  if(!stroke.atoms.length) return;
+  if(document.getElementById("erase-burn").checked){
+    for(const rec of stroke.atoms){
+      if(!rec.src) continue;                       // clutter has no template
+      const L=S.layers[rec.src.li];
+      const idx=L.template.indexOf(rec.src.ref);
+      if(idx>=0){L.template.splice(idx,1);stroke.tmpl.push(rec.src);}
+    }
+  }
+  eraseStack.push(stroke);
+  updateEraseButtons();
+  refreshOwnership();drawOverlay();renderLayerList();renderLibrary();
+}
+function undoErase(redraw=true){
+  const stroke=eraseStack.pop();
+  if(!stroke) return;
+  for(const t of stroke.tmpl) S.layers[t.li].template.push(t.ref);
+  for(const rec of stroke.atoms){
+    S.obs.push(rec.a);S.gt.push(rec.gt);S.src.push(rec.src);S.evid.push(rec.evid);
+    if(S.assign)S.assign.push(rec.assign??-1);
+    if(S.marg)S.marg.push(rec.marg);
+  }
+  updateEraseButtons();
+  if(redraw){
+    rebuildGroupBuffers();renderScene();refreshOwnership();
+    drawOverlay();updatePanels();renderLayerList();renderLibrary();
+  }
+}
+function restoreAllErases(){
+  while(eraseStack.length) undoErase(false);
+  rebuildGroupBuffers();renderScene();refreshOwnership();
+  drawOverlay();updatePanels();renderLayerList();renderLibrary();
+}
+
 /* ------------- pointer interaction ------------- */
 let drag=null;
 overC.addEventListener("pointerdown",e=>{
@@ -1148,6 +1353,13 @@ overC.addEventListener("pointerdown",e=>{
     }
     return;
   }
+  if(toolMode()==="erase"){                 // erase works in soup AND bound
+    drag={erase:true,stroke:{atoms:[],tmpl:[]}};
+    overC.setPointerCapture(e.pointerId);
+    lastCursor=[wx,wy];
+    eraseAt(wx,wy,drag.stroke);
+    return;
+  }
   if(S.phase!=="bound") return;
   let best=-1,bd=0.12*0.12;
   for(let i=0;i<S.obs.length;i++){
@@ -1167,19 +1379,25 @@ overC.addEventListener("pointerdown",e=>{
   overC.setPointerCapture(e.pointerId);
 });
 overC.addEventListener("pointermove",e=>{
-  if(!drag) return;
   const rect=overC.getBoundingClientRect();
   const wx=p2w((e.clientX-rect.left)*overC.width/rect.width);
   const wy=p2w((e.clientY-rect.top)*overC.width/rect.width);
+  if(toolMode()==="erase") lastCursor=[wx,wy];
+  if(!drag){ if(toolMode()==="erase") drawOverlay(); return; }
+  if(drag.erase){ eraseAt(wx,wy,drag.stroke); return; }
   const dx=wx-drag.lx,dy=wy-drag.ly;
   if(dx||dy){applyGesture(drag.k,gestureTranslate(dx,dy));drag.lx=wx;drag.ly=wy;drag.moved=true;}
 });
 overC.addEventListener("pointerup",e=>{
   if(!drag) return;
+  if(drag.erase){ commitStroke(drag.stroke); drag=null; return; }
   overC.classList.remove("dragging");
   if(drag.moved) resettle(drag.k,S.mu[drag.k]);
   drag=null;
 });
+overC.addEventListener("pointerleave",()=>{
+  if(lastCursor){ lastCursor=null; drawOverlay(); }
+});
 overC.addEventListener("wheel",e=>{
   if(S.phase!=="bound") return;
   const rect=overC.getBoundingClientRect();
@@ -1480,6 +1698,48 @@ document.getElementById("auto-occ").addEventListener("change",()=>{
   if(S.phase==="bound"){occlusionRefresh(false);renderScene();}
 });
 
+/* ------------- edit & look wiring (Bet 9) ------------- */
+document.getElementById("btn-undo-erase").addEventListener("click",()=>undoErase());
+document.getElementById("btn-restore-erase").addEventListener("click",restoreAllErases);
+document.querySelectorAll('input[name=tool]').forEach(el=>el.addEventListener("change",()=>{
+  stage.classList.toggle("erasing",toolMode()==="erase");
+  if(toolMode()!=="erase") lastCursor=null;
+  drawOverlay();
+}));
+document.querySelectorAll('input[name=brush]').forEach(el=>el.addEventListener("change",drawOverlay));
+document.getElementById("bg-color").addEventListener("input",e=>{
+  const h=e.target.value;
+  backdrop.rgb=[parseInt(h.slice(1,3),16),parseInt(h.slice(3,5),16),parseInt(h.slice(5,7),16)];
+  backdrop.custom=true;renderScene();
+});
+document.getElementById("bg-file").addEventListener("change",e=>{
+  const f=e.target.files[0];if(!f)return;
+  const img=new Image();
+  img.onload=()=>{
+    const c=document.createElement("canvas");c.width=c.height=RES;
+    const sc=Math.max(RES/img.width,RES/img.height);      // cover-crop
+    c.getContext("2d").drawImage(img,(RES-img.width*sc)/2,(RES-img.height*sc)/2,img.width*sc,img.height*sc);
+    backdrop.img=c.getContext("2d").getImageData(0,0,RES,RES).data;
+    backdrop.custom=true;renderScene();
+    URL.revokeObjectURL(img.src);
+  };
+  img.src=URL.createObjectURL(f);
+});
+document.getElementById("btn-bg-clear").addEventListener("click",()=>{
+  backdrop.img=null;document.getElementById("bg-file").value="";
+  renderScene();
+});
+for(const [id,set] of [
+  ["g-coarse",v=>GAINS.band[0]=v],["g-mid",v=>GAINS.band[1]=v],
+  ["g-fine",v=>GAINS.band[2]=v],["g-op",v=>GAINS.opacity=v]]){
+  const el=document.getElementById(id);
+  el.addEventListener("input",()=>{
+    const v=el.value/100; set(v);
+    document.getElementById(id+"-v").textContent=v.toFixed(2);
+    renderScene();
+  });
+}
+
 /* ------------- boot ------------- */
 document.getElementById("btn-scramble").addEventListener("click",scramble);
 document.getElementById("btn-bind").addEventListener("click",()=>bind(true));

studio/studio_core.js

@@ -107,6 +107,47 @@ function trimAtoms(atoms, sigMax = 0.35) {
   return kept.map(a => { const b = a.slice(); b[0] -= mx; b[1] -= my; return b; });
 }
 
+/* ---- Bet 9 additions: eraser + backdrop + band gains (pure, testable) ---- */
+
+/* Frequency band of an atom. f is cycles/unit; the frame spans 2 units, so
+   cycles-per-image = 2f. Bands follow the original splatstack dials:
+   coarse < 4 c/img, mid 4–10, fine > 10.  Returns 0|1|2. */
+const BAND_EDGES = [2.0, 5.0];
+function bandOf(f) { return f < BAND_EDGES[0] ? 0 : f < BAND_EDGES[1] ? 1 : 2; }
+
+/* Erase mask: true for atoms whose center falls inside the brush circle.
+   skip(i) can veto (e.g. atoms of hidden layers stay untouched). */
+function eraseMask(obs, wx, wy, r, skip) {
+  const r2 = r * r;
+  return obs.map((a, i) => {
+    if (skip && skip(i)) return false;
+    const dx = a[0] - wx, dy = a[1] - wy;
+    return dx * dx + dy * dy < r2;
+  });
+}
+
+/* Composite an already-sigmoided field over a backdrop.
+   img: Uint8ClampedArray RGBA from sigmoidField/compositePainter (mutated).
+   alpha: Float32Array(H*H) from alphaFromPre of the (band-gained) pre field.
+   opacity: global gain on alpha, clamped to [0,1] per pixel.
+   bg: either [r,g,b] flat color or a Uint8ClampedArray(4*H*H) RGBA image.
+   Identity check: with alpha==1 everywhere or bg==the field itself the
+   output is unchanged; with opacity such that a==1 the field wins. */
+function blendOverBackdrop(img, alpha, opacity, bg, H) {
+  const n = H * H;
+  const flat = !(bg && bg.length === 4 * n);
+  for (let i = 0; i < n; i++) {
+    const a = Math.min(1, alpha[i] * opacity);
+    const br = flat ? bg[0] : bg[4 * i],
+          bgr = flat ? bg[1] : bg[4 * i + 1],
+          bb = flat ? bg[2] : bg[4 * i + 2];
+    img[4 * i]     = br  + a * (img[4 * i]     - br);
+    img[4 * i + 1] = bgr + a * (img[4 * i + 1] - bgr);
+    img[4 * i + 2] = bb  + a * (img[4 * i + 2] - bb);
+  }
+  return img;
+}
+
 /* Sim(2) composition in vote coordinates: (g2 ∘ g1). */
 function composePose(g2, g1) {
   const s2 = Math.exp(g2[3]);
@@ -131,5 +172,6 @@ if (typeof module !== "undefined") {
     ALPHA_C, COVER_THRESH, alphaFromPre, coverageOf, autoHidden,
     compositePainter, composePose, gestureTranslate, gestureRotateAbout,
     gestureScaleAbout, trimAtoms,
+    BAND_EDGES, bandOf, eraseMask, blendOverBackdrop,
   };
 }

studio_core.js

@@ -107,6 +107,47 @@ function trimAtoms(atoms, sigMax = 0.35) {
   return kept.map(a => { const b = a.slice(); b[0] -= mx; b[1] -= my; return b; });
 }
 
+/* ---- Bet 9 additions: eraser + backdrop + band gains (pure, testable) ---- */
+
+/* Frequency band of an atom. f is cycles/unit; the frame spans 2 units, so
+   cycles-per-image = 2f. Bands follow the original splatstack dials:
+   coarse < 4 c/img, mid 4–10, fine > 10.  Returns 0|1|2. */
+const BAND_EDGES = [2.0, 5.0];
+function bandOf(f) { return f < BAND_EDGES[0] ? 0 : f < BAND_EDGES[1] ? 1 : 2; }
+
+/* Erase mask: true for atoms whose center falls inside the brush circle.
+   skip(i) can veto (e.g. atoms of hidden layers stay untouched). */
+function eraseMask(obs, wx, wy, r, skip) {
+  const r2 = r * r;
+  return obs.map((a, i) => {
+    if (skip && skip(i)) return false;
+    const dx = a[0] - wx, dy = a[1] - wy;
+    return dx * dx + dy * dy < r2;
+  });
+}
+
+/* Composite an already-sigmoided field over a backdrop.
+   img: Uint8ClampedArray RGBA from sigmoidField/compositePainter (mutated).
+   alpha: Float32Array(H*H) from alphaFromPre of the (band-gained) pre field.
+   opacity: global gain on alpha, clamped to [0,1] per pixel.
+   bg: either [r,g,b] flat color or a Uint8ClampedArray(4*H*H) RGBA image.
+   Identity check: with alpha==1 everywhere or bg==the field itself the
+   output is unchanged; with opacity such that a==1 the field wins. */
+function blendOverBackdrop(img, alpha, opacity, bg, H) {
+  const n = H * H;
+  const flat = !(bg && bg.length === 4 * n);
+  for (let i = 0; i < n; i++) {
+    const a = Math.min(1, alpha[i] * opacity);
+    const br = flat ? bg[0] : bg[4 * i],
+          bgr = flat ? bg[1] : bg[4 * i + 1],
+          bb = flat ? bg[2] : bg[4 * i + 2];
+    img[4 * i]     = br  + a * (img[4 * i]     - br);
+    img[4 * i + 1] = bgr + a * (img[4 * i + 1] - bgr);
+    img[4 * i + 2] = bb  + a * (img[4 * i + 2] - bb);
+  }
+  return img;
+}
+
 /* Sim(2) composition in vote coordinates: (g2 ∘ g1). */
 function composePose(g2, g1) {
   const s2 = Math.exp(g2[3]);
@@ -131,5 +172,6 @@ if (typeof module !== "undefined") {
     ALPHA_C, COVER_THRESH, alphaFromPre, coverageOf, autoHidden,
     compositePainter, composePose, gestureTranslate, gestureRotateAbout,
     gestureScaleAbout, trimAtoms,
+    BAND_EDGES, bandOf, eraseMask, blendOverBackdrop,
   };
 }

studio_ui.html

@@ -72,6 +72,11 @@ button.primary{border-color:var(--phosphor);color:var(--phosphor)}
 label.tog{display:flex;gap:8px;align-items:center;cursor:pointer;padding:2px 0;font-size:12px}
 label.tog input{accent-color:var(--phosphor)}
 input[type=range]{flex:1;accent-color:var(--phosphor)}
+.gain-row{display:grid;grid-template-columns:54px 1fr 40px;gap:6px;align-items:center;margin-top:3px}
+.gain-row input[type=range]{width:100%;margin:0}
+.gain-row .val{text-align:right}
+input[type=color]{width:36px;height:22px;padding:1px;border:1px solid var(--panel-edge);background:var(--well);border-radius:4px;cursor:pointer}
+#stage.erasing #overlay-canvas{cursor:crosshair}
 input[type=text],textarea{font-family:var(--mono);font-size:12px;background:var(--well);
   color:var(--ink);border:1px solid var(--panel-edge);border-radius:4px;padding:6px 8px;width:100%}
 input[type=text]:focus-visible,textarea:focus-visible{outline:2px solid var(--phosphor);border-color:transparent}
@@ -99,7 +104,7 @@ input[type=file]{font-size:10.5px;color:var(--muted);max-width:170px}
     <div id="stage">
       <canvas id="scene-canvas"></canvas>
       <canvas id="overlay-canvas"></canvas>
-      <div class="hint">drag = pose clamp &middot; wheel rotate &middot; shift+wheel scale &middot; shift+click = semantic hint for selected layer</div>
+      <div class="hint">drag = pose clamp &middot; wheel rotate &middot; shift+wheel scale &middot; shift+click = hint &middot; erase tool: brush deletes atoms</div>
     </div>
   </div>
 
@@ -129,6 +134,36 @@ input[type=file]{font-size:10.5px;color:var(--muted);max-width:170px}
       </div>
     </div>
 
+    <div class="card">
+      <h2>EDIT &amp; LOOK</h2>
+      <div class="row">
+        <span class="dim">tool</span>
+        <label class="tog"><input type="radio" name="tool" value="pose" checked> pose</label>
+        <label class="tog"><input type="radio" name="tool" value="erase"> erase</label>
+        <span class="spacer"></span>
+        <span class="dim">brush</span>
+        <label class="tog"><input type="radio" name="brush" value="0.05"> S</label>
+        <label class="tog"><input type="radio" name="brush" value="0.12" checked> M</label>
+        <label class="tog"><input type="radio" name="brush" value="0.25"> L</label>
+      </div>
+      <div class="row">
+        <button id="btn-undo-erase" disabled>Undo erase</button>
+        <button id="btn-restore-erase" disabled>Restore all</button>
+        <label class="tog"><input type="checkbox" id="erase-burn"> burn into template</label>
+      </div>
+      <div class="row">
+        <span class="dim">backdrop</span>
+        <input type="color" id="bg-color" value="#808080" title="backdrop color">
+        <input type="file" id="bg-file" accept="image/*" style="max-width:46%">
+        <button id="btn-bg-clear">clear img</button>
+      </div>
+      <div class="gain-row"><span class="dim">coarse</span><input type="range" id="g-coarse" min="0" max="200" value="100"><span class="val readout" id="g-coarse-v">1.00</span></div>
+      <div class="gain-row"><span class="dim">mid</span><input type="range" id="g-mid" min="0" max="200" value="100"><span class="val readout" id="g-mid-v">1.00</span></div>
+      <div class="gain-row"><span class="dim">fine</span><input type="range" id="g-fine" min="0" max="200" value="100"><span class="val readout" id="g-fine-v">1.00</span></div>
+      <div class="gain-row"><span class="dim">opacity</span><input type="range" id="g-op" min="0" max="200" value="100"><span class="val readout" id="g-op-v">1.00</span></div>
+      <div class="dim" style="font-size:10.5px;margin-top:6px">Erase deletes atoms under the brush (render only, until <b>burn</b> writes it into the layer template; Scramble/Bind rebuild the scene from templates). Undo works until the next Bind. Backdrop is presentation and survives everything. Band gains (coarse&lt;4, mid 4&ndash;10, fine&gt;10&nbsp;c/img) scale atom colors in field mode; opacity blends the whole field over the backdrop.</div>
+    </div>
+
     <div class="card">
       <h2>LAYERS <span class="dim" style="letter-spacing:0">(front is highest)</span></h2>
       <div id="layer-list"></div>
@@ -177,7 +212,7 @@ input[type=file]{font-size:10.5px;color:var(--muted);max-width:170px}
     <div class="card" id="ledger">
       <details>
         <summary>HONEST LEDGER</summary>
-        <p><b>Verified in this build:</b> the BP core matches the SlapstackBet6 Python (transform 2e-16, render MSE 8.6e-8, identical binding); drag = pose clamp + re-settle; identity persists through occlusion; depth occlusion removes evidence honestly (marginals revert toward the prior, coverage releases when moved away); the semantic likelihood factor resolves the twins case (two identical stars: 0.05 acc on geometry alone, 0.99 with location priors) and a mildly wrong prior is overridden by evidence; image&rarr;layer fitting runs end to end on CPU.</p>
+        <p><b>Verified in this build:</b> the BP core matches the SlapstackBet6 Python (transform 2e-16, render MSE 8.6e-8, identical binding); drag = pose clamp + re-settle; identity persists through occlusion; depth occlusion removes evidence honestly (marginals revert toward the prior, coverage releases when moved away); the semantic likelihood factor resolves the twins case (two identical stars: 0.05 acc on geometry alone, 0.99 with location priors) and a mildly wrong prior is overridden by evidence; image&rarr;layer fitting runs end to end on CPU. <b>Bet 9:</b> the eraser filters per-atom state (order-free, so undo is re-append), burn edits the template so erases survive rebuilds; the backdrop is pure presentation and persists across Bind/Scramble; band gains exploit render linearity (gain&middot;color &equiv; gain&middot;contribution), verified in tests_edit.js.</p>
         <p><span class="no">Not verified:</span> text&rarr;layer (SDS) and cross-attention matte are line-for-line adaptations of the verified Bet-5 GPU loop but have NOT been executed on a GPU — first run is a smoke test; SD attention maps flicker across seeds, which is why they enter BP as a prior with a weight, never as truth. Real-photo scene&rarr;atoms remains open. Painter compositing and the alpha matte are presentation choices, not the additive field model.</p>
       </details>
     </div>
@@ -221,6 +256,19 @@ const S = {
 };
 let nextDepth = 1, nextId = 1;
 
+/* ---- Bet 9: eraser / backdrop / band-gain state ---- */
+const GAINS = { band: [1, 1, 1], opacity: 1 };
+const backdrop = { custom: false, rgb: [128, 128, 128], img: null }; // img: RGBA RES*RES
+let bandPre = null, bandDirty = true;
+const fieldAlpha = new Float32Array(RES * RES);
+let eraseStack = [], lastCursor = null;
+function toolMode(){ return document.querySelector('input[name=tool]:checked').value; }
+function brushR(){ return +document.querySelector('input[name=brush]:checked').value; }
+function updateEraseButtons(){
+  document.getElementById("btn-undo-erase").disabled = !eraseStack.length;
+  document.getElementById("btn-restore-erase").disabled = !eraseStack.length;
+}
+
 function addLayer(name, template, autoPlace) {
   const [color, rgb] = PALETTE[(S.layers.length) % PALETTE.length];
   const L = { id: nextId++, name, color, rgb, template, placed: false,
@@ -249,17 +297,19 @@ function rand(){ rngState=(rngState*1103515245+12345)&0x7fffffff; return rngStat
 function rebuildScene() {
   S.placed = S.layers.map((L,i)=>L.placed?i:-1).filter(i=>i>=0);
   const noiseAmt = 0.006 * Math.pow(3, +document.getElementById("noise").value / 3);
-  S.obs = []; S.gt = [];
+  S.obs = []; S.gt = []; S.src = [];
   S.placed.forEach((li,k)=>{
-    for (const a of transformAtoms(S.layers[li].template, S.layers[li].pose)) {
-      S.obs.push(a); S.gt.push(k);
+    const tmpl = S.layers[li].template;
+    const tr = transformAtoms(tmpl, S.layers[li].pose);
+    for (let j = 0; j < tr.length; j++) {
+      S.obs.push(tr[j]); S.gt.push(k); S.src.push({ li, ref: tmpl[j] });
     }
   });
   for (let i=0;i<12;i++){
     const su=0.04+0.08*rand();
     S.obs.push([-0.95+1.9*rand(),-0.95+1.9*rand(),-Math.PI/2+Math.PI*rand(),
       su,su*(0.4+0.5*rand()),4+10*rand(),TAU*rand(),rand(),rand(),rand()]);
-    S.gt.push(-1);
+    S.gt.push(-1); S.src.push(null);
   }
   for (const a of S.obs) for(let q=0;q<10;q++){
     const g=Math.sqrt(-2*Math.log(rand()+1e-9))*Math.cos(TAU*rand());
@@ -271,6 +321,7 @@ function rebuildScene() {
   S.covFrac=S.placed.map(()=>0);
   S.coastT=S.placed.map(()=>0);
   S.ownField=null;
+  eraseStack=[]; updateEraseButtons();
   setPhase("soup");
   rebuildGroupBuffers();
   renderScene(); drawOverlay(); renderLayerList(); renderLibrary(); updatePanels();
@@ -328,12 +379,28 @@ function rebuildGroupBuffers(){
     renderPre([S.obs[i]],RES,S.groupPre[g]);
   }
   for(let g=0;g<=K;g++) S.groupAlpha.push(alphaFromPre(S.groupPre[g],RES));
+  bandDirty=true;
 }
 function rebuildOneGroup(k){
   S.groupPre[k]=new Float32Array(3*RES*RES);
   if(!S.layers[S.placed[k]].hidden)
     renderPre(groupAtomIdx(k).map(i=>S.obs[i]),RES,S.groupPre[k]);
   S.groupAlpha[k]=alphaFromPre(S.groupPre[k],RES);
+  bandDirty=true;
+}
+/* frequency-band buffers, built lazily only when a band gain != 1.
+   Same visibility rule as the group buffers; render is linear in atom color,
+   so gain*color == gain*contribution and Σ_b gain_b·bandPre_b is exact. */
+function rebuildBandBuffers(){
+  const K=S.placed.length;
+  bandPre=[new Float32Array(3*RES*RES),new Float32Array(3*RES*RES),new Float32Array(3*RES*RES)];
+  const groupOf=i=>{ const g=S.marg?believedGroup(i):S.gt[i]; return g>=0?g:K; };
+  for(let i=0;i<S.obs.length;i++){
+    const g=groupOf(i);
+    if(g<K && S.layers[S.placed[g]].hidden) continue;
+    renderPre([S.obs[i]],RES,bandPre[bandOf(S.obs[i][5])]);
+  }
+  bandDirty=false;
 }
 const sceneCtx=sceneC.getContext("2d");
 const compositePre=new Float32Array(3*RES*RES);
@@ -341,16 +408,40 @@ const sceneImg=new ImageData(RES,RES);
 function compMode(){ return document.querySelector('input[name=comp]:checked').value; }
 function renderScene(){
   const K=S.placed.length;
+  const gb=GAINS.band, gainsOn=gb[0]!==1||gb[1]!==1||gb[2]!==1;
+  const bgOn=backdrop.custom||backdrop.img||GAINS.opacity!==1;
   if(compMode()==="field"){
     compositePre.fill(0);
-    for(const buf of S.groupPre)
-      for(let i=0;i<compositePre.length;i++) compositePre[i]+=buf[i];
+    if(gainsOn){
+      if(bandDirty) rebuildBandBuffers();
+      for(let b=0;b<3;b++){
+        const g=gb[b]; if(!g) continue;
+        const buf=bandPre[b];
+        for(let i=0;i<compositePre.length;i++) compositePre[i]+=g*buf[i];
+      }
+    } else {
+      for(const buf of S.groupPre)
+        for(let i=0;i<compositePre.length;i++) compositePre[i]+=buf[i];
+    }
     sigmoidField(compositePre,RES,sceneImg.data);
+    if(bgOn){
+      alphaFromPre(compositePre,RES,fieldAlpha);
+      blendOverBackdrop(sceneImg.data,fieldAlpha,GAINS.opacity,backdrop.img||backdrop.rgb,RES);
+    }
   } else {
     // painter: clutter at the back, then placed layers by depth
     const order=[K, ...S.placed.map((li,k)=>k)
       .sort((a,b)=>S.layers[S.placed[a]].depth-S.layers[S.placed[b]].depth)];
     compositePainter(order,S.groupPre,S.groupAlpha,RES,sceneImg.data);
+    if(bgOn){
+      // union alpha of everything rendered (band gains are field-mode only)
+      for(let i=0;i<RES*RES;i++){
+        let keep=1;
+        for(let q=0;q<=K;q++) keep*=1-S.groupAlpha[q][i];
+        fieldAlpha[i]=1-keep;
+      }
+      blendOverBackdrop(sceneImg.data,fieldAlpha,GAINS.opacity,backdrop.img||backdrop.rgb,RES);
+    }
   }
   sceneCtx.putImageData(sceneImg,0,0);
 }
@@ -460,6 +551,14 @@ function drawOverlay(){
       }
     }
   }
+
+  if(toolMode()==="erase"&&lastCursor){       // eraser brush cursor
+    ctx.strokeStyle="rgba(255,120,110,0.9)";
+    ctx.lineWidth=1.4*px1;ctx.setLineDash([4*px1,3*px1]);
+    ctx.beginPath();
+    ctx.arc(w2p(lastCursor[0]),w2p(lastCursor[1]),brushR()*overC.width/2,0,TAU);
+    ctx.stroke();ctx.setLineDash([]);
+  }
 }
 
 /* ------------- semantic factor from hints ------------- */
@@ -516,6 +615,7 @@ function runBind(opts={}){
 function bind(animate=true){
   if(S.phase==="binding"||!S.placed.length) return;
   S.assign=null;
+  eraseStack=[]; updateEraseButtons();   // erase history is stale once BP re-runs
   S.evid=S.obs.map(()=>true);      // full re-bind: everything is evidence again
   for(const li of S.placed) if(S.layers[li].hidden){
     // user-hidden layers stay evidence-free
@@ -599,6 +699,70 @@ function applyGesture(k,g){
   renderScene();drawOverlay();updatePanels();
 }
 
+/* ------------- eraser (Bet 9) -------------
+   Deleting an atom = filtering every per-atom parallel array by the brush
+   mask. Order of atoms carries no meaning anywhere (additive render, per-atom
+   marginals), so undo can simply re-append the removed records.
+   Undo is valid until the next Bind/Scramble/place/remove (those rebuild or
+   re-infer the per-atom state). "Burn" additionally removes the source atom
+   from the layer TEMPLATE, so the erase survives scene rebuilds. */
+function eraseAt(wx,wy,stroke){
+  const skip=i=>{ const g=believedGroup(i); return g>=0&&S.layers[S.placed[g]].hidden; };
+  const mask=eraseMask(S.obs,wx,wy,brushR(),skip);
+  let any=false; for(const m of mask) if(m){any=true;break;}
+  if(!any) return;
+  const kObs=[],kGt=[],kSrc=[],kEvid=[],
+        kAssign=S.assign?[]:null, kMarg=S.marg?[]:null;
+  for(let i=0;i<S.obs.length;i++){
+    if(mask[i]){
+      stroke.atoms.push({a:S.obs[i],gt:S.gt[i],src:S.src[i],evid:S.evid[i],
+        assign:S.assign?S.assign[i]:null, marg:S.marg?S.marg[i]:null});
+    } else {
+      kObs.push(S.obs[i]);kGt.push(S.gt[i]);kSrc.push(S.src[i]);kEvid.push(S.evid[i]);
+      if(kAssign)kAssign.push(S.assign[i]);
+      if(kMarg)kMarg.push(S.marg[i]);
+    }
+  }
+  S.obs=kObs;S.gt=kGt;S.src=kSrc;S.evid=kEvid;
+  if(kAssign)S.assign=kAssign;
+  if(kMarg)S.marg=kMarg;
+  rebuildGroupBuffers();renderScene();drawOverlay();updatePanels();
+}
+function commitStroke(stroke){
+  if(!stroke.atoms.length) return;
+  if(document.getElementById("erase-burn").checked){
+    for(const rec of stroke.atoms){
+      if(!rec.src) continue;                       // clutter has no template
+      const L=S.layers[rec.src.li];
+      const idx=L.template.indexOf(rec.src.ref);
+      if(idx>=0){L.template.splice(idx,1);stroke.tmpl.push(rec.src);}
+    }
+  }
+  eraseStack.push(stroke);
+  updateEraseButtons();
+  refreshOwnership();drawOverlay();renderLayerList();renderLibrary();
+}
+function undoErase(redraw=true){
+  const stroke=eraseStack.pop();
+  if(!stroke) return;
+  for(const t of stroke.tmpl) S.layers[t.li].template.push(t.ref);
+  for(const rec of stroke.atoms){
+    S.obs.push(rec.a);S.gt.push(rec.gt);S.src.push(rec.src);S.evid.push(rec.evid);
+    if(S.assign)S.assign.push(rec.assign??-1);
+    if(S.marg)S.marg.push(rec.marg);
+  }
+  updateEraseButtons();
+  if(redraw){
+    rebuildGroupBuffers();renderScene();refreshOwnership();
+    drawOverlay();updatePanels();renderLayerList();renderLibrary();
+  }
+}
+function restoreAllErases(){
+  while(eraseStack.length) undoErase(false);
+  rebuildGroupBuffers();renderScene();refreshOwnership();
+  drawOverlay();updatePanels();renderLayerList();renderLibrary();
+}
+
 /* ------------- pointer interaction ------------- */
 let drag=null;
 overC.addEventListener("pointerdown",e=>{
@@ -615,6 +779,13 @@ overC.addEventListener("pointerdown",e=>{
     }
     return;
   }
+  if(toolMode()==="erase"){                 // erase works in soup AND bound
+    drag={erase:true,stroke:{atoms:[],tmpl:[]}};
+    overC.setPointerCapture(e.pointerId);
+    lastCursor=[wx,wy];
+    eraseAt(wx,wy,drag.stroke);
+    return;
+  }
   if(S.phase!=="bound") return;
   let best=-1,bd=0.12*0.12;
   for(let i=0;i<S.obs.length;i++){
@@ -634,19 +805,25 @@ overC.addEventListener("pointerdown",e=>{
   overC.setPointerCapture(e.pointerId);
 });
 overC.addEventListener("pointermove",e=>{
-  if(!drag) return;
   const rect=overC.getBoundingClientRect();
   const wx=p2w((e.clientX-rect.left)*overC.width/rect.width);
   const wy=p2w((e.clientY-rect.top)*overC.width/rect.width);
+  if(toolMode()==="erase") lastCursor=[wx,wy];
+  if(!drag){ if(toolMode()==="erase") drawOverlay(); return; }
+  if(drag.erase){ eraseAt(wx,wy,drag.stroke); return; }
   const dx=wx-drag.lx,dy=wy-drag.ly;
   if(dx||dy){applyGesture(drag.k,gestureTranslate(dx,dy));drag.lx=wx;drag.ly=wy;drag.moved=true;}
 });
 overC.addEventListener("pointerup",e=>{
   if(!drag) return;
+  if(drag.erase){ commitStroke(drag.stroke); drag=null; return; }
   overC.classList.remove("dragging");
   if(drag.moved) resettle(drag.k,S.mu[drag.k]);
   drag=null;
 });
+overC.addEventListener("pointerleave",()=>{
+  if(lastCursor){ lastCursor=null; drawOverlay(); }
+});
 overC.addEventListener("wheel",e=>{
   if(S.phase!=="bound") return;
   const rect=overC.getBoundingClientRect();
@@ -947,6 +1124,48 @@ document.getElementById("auto-occ").addEventListener("change",()=>{
   if(S.phase==="bound"){occlusionRefresh(false);renderScene();}
 });
 
+/* ------------- edit & look wiring (Bet 9) ------------- */
+document.getElementById("btn-undo-erase").addEventListener("click",()=>undoErase());
+document.getElementById("btn-restore-erase").addEventListener("click",restoreAllErases);
+document.querySelectorAll('input[name=tool]').forEach(el=>el.addEventListener("change",()=>{
+  stage.classList.toggle("erasing",toolMode()==="erase");
+  if(toolMode()!=="erase") lastCursor=null;
+  drawOverlay();
+}));
+document.querySelectorAll('input[name=brush]').forEach(el=>el.addEventListener("change",drawOverlay));
+document.getElementById("bg-color").addEventListener("input",e=>{
+  const h=e.target.value;
+  backdrop.rgb=[parseInt(h.slice(1,3),16),parseInt(h.slice(3,5),16),parseInt(h.slice(5,7),16)];
+  backdrop.custom=true;renderScene();
+});
+document.getElementById("bg-file").addEventListener("change",e=>{
+  const f=e.target.files[0];if(!f)return;
+  const img=new Image();
+  img.onload=()=>{
+    const c=document.createElement("canvas");c.width=c.height=RES;
+    const sc=Math.max(RES/img.width,RES/img.height);      // cover-crop
+    c.getContext("2d").drawImage(img,(RES-img.width*sc)/2,(RES-img.height*sc)/2,img.width*sc,img.height*sc);
+    backdrop.img=c.getContext("2d").getImageData(0,0,RES,RES).data;
+    backdrop.custom=true;renderScene();
+    URL.revokeObjectURL(img.src);
+  };
+  img.src=URL.createObjectURL(f);
+});
+document.getElementById("btn-bg-clear").addEventListener("click",()=>{
+  backdrop.img=null;document.getElementById("bg-file").value="";
+  renderScene();
+});
+for(const [id,set] of [
+  ["g-coarse",v=>GAINS.band[0]=v],["g-mid",v=>GAINS.band[1]=v],
+  ["g-fine",v=>GAINS.band[2]=v],["g-op",v=>GAINS.opacity=v]]){
+  const el=document.getElementById(id);
+  el.addEventListener("input",()=>{
+    const v=el.value/100; set(v);
+    document.getElementById(id+"-v").textContent=v.toFixed(2);
+    renderScene();
+  });
+}
+
 /* ------------- boot ------------- */
 document.getElementById("btn-scramble").addEventListener("click",scramble);
 document.getElementById("btn-bind").addEventListener("click",()=>bind(true));

tests_edit.js

@@ -0,0 +1,141 @@
+/* Bet 9 battery — eraser / backdrop / band gains, tested headless.
+   1. bandOf edges match the declared bands
+   2. band-gain linearity: sum_b gain_b * render(band_b) == render(gain-scaled colors), exactly
+   3. blendOverBackdrop: identities (a=1 field wins, a=0 backdrop wins), image backdrop path
+   4. eraseMask geometry + skip veto
+   5. erase -> undo round-trip: rendered field identical (order-free re-append)
+   6. burn-to-template: template loses exactly the erased refs; undo restores them
+*/
+"use strict";
+const C = require("./studio/core.js");
+const SC = require("./studio/studio_core.js");
+
+let go = 0, fail = 0;
+function T(name, ok, note) {
+  console.log((ok ? "GO  " : "FAIL") + " " + name + (note ? "  [" + note + "]" : ""));
+  ok ? go++ : fail++;
+}
+const rnd = (() => { let s = 424242; return () => (s = (s * 1103515245 + 12345) & 0x7fffffff) / 0x7fffffff; })();
+function randAtoms(n) {
+  const out = [];
+  for (let i = 0; i < n; i++) {
+    const su = 0.03 + 0.1 * rnd();
+    out.push([-0.8 + 1.6 * rnd(), -0.8 + 1.6 * rnd(), Math.PI * rnd(),
+      su, su * (0.4 + 0.5 * rnd()), 0.6 + 9 * rnd(), 2 * Math.PI * rnd(),
+      -1 + 2 * rnd(), -1 + 2 * rnd(), -1 + 2 * rnd()]);
+  }
+  return out;
+}
+const H = 64;
+
+/* 1 ------------------------------------------------------------------ */
+T("bandOf edges", SC.bandOf(1.99) === 0 && SC.bandOf(2.0) === 1 &&
+  SC.bandOf(4.99) === 1 && SC.bandOf(5.0) === 2, "edges at f=2,5 (4 & 10 c/img)");
+
+/* 2 band-gain linearity ---------------------------------------------- */
+{
+  const atoms = randAtoms(40);
+  const gains = [0.3, 1.7, 0.0];
+  // path A: per-band buffers scaled at composite time
+  const bands = [new Float32Array(3 * H * H), new Float32Array(3 * H * H), new Float32Array(3 * H * H)];
+  for (const a of atoms) C.renderPre([a], H, bands[SC.bandOf(a[5])]);
+  const A = new Float32Array(3 * H * H);
+  for (let b = 0; b < 3; b++) for (let i = 0; i < A.length; i++) A[i] += gains[b] * bands[b][i];
+  // path B: gain baked into atom colors, rendered once
+  const scaled = atoms.map(a => {
+    const g = gains[SC.bandOf(a[5])], c = a.slice();
+    c[7] *= g; c[8] *= g; c[9] *= g; return c;
+  });
+  const B = C.renderPre(scaled, H);
+  let maxd = 0;
+  for (let i = 0; i < A.length; i++) maxd = Math.max(maxd, Math.abs(A[i] - B[i]));
+  T("band gains exact by render linearity", maxd < 1e-6, "max |A-B| = " + maxd.toExponential(1));
+}
+
+/* 3 backdrop blending -------------------------------------------------*/
+{
+  const atoms = randAtoms(25);
+  const pre = C.renderPre(atoms, H);
+  const img0 = C.sigmoidField(pre, H);
+  const alpha = SC.alphaFromPre(pre, H);
+
+  // a) alpha forced to 1 -> field unchanged
+  const one = new Float32Array(H * H).fill(1);
+  const imgA = new Uint8ClampedArray(img0);
+  SC.blendOverBackdrop(imgA, one, 1, [10, 200, 30], H);
+  let d = 0; for (let i = 0; i < imgA.length; i++) d = Math.max(d, Math.abs(imgA[i] - img0[i]));
+  T("alpha=1: field wins everywhere", d === 0, "max delta " + d);
+
+  // b) opacity 0 -> pure backdrop color
+  const imgB = new Uint8ClampedArray(img0);
+  SC.blendOverBackdrop(imgB, alpha, 0, [10, 200, 30], H);
+  let ok = true;
+  for (let i = 0; i < H * H; i++)
+    if (imgB[4 * i] !== 10 || imgB[4 * i + 1] !== 200 || imgB[4 * i + 2] !== 30) { ok = false; break; }
+  T("opacity=0: backdrop wins everywhere", ok);
+
+  // c) image backdrop path: where alpha==0 the backdrop image shows verbatim
+  const bg = new Uint8ClampedArray(4 * H * H);
+  for (let i = 0; i < H * H; i++) { bg[4 * i] = i % 251; bg[4 * i + 1] = (2 * i) % 251; bg[4 * i + 2] = (3 * i) % 251; bg[4 * i + 3] = 255; }
+  const imgC = new Uint8ClampedArray(img0);
+  SC.blendOverBackdrop(imgC, alpha, 1, bg, H);
+  ok = true;
+  let checked = 0;
+  for (let i = 0; i < H * H; i++) if (alpha[i] === 0) {
+    checked++;
+    if (imgC[4 * i] !== bg[4 * i] || imgC[4 * i + 1] !== bg[4 * i + 1] || imgC[4 * i + 2] !== bg[4 * i + 2]) { ok = false; break; }
+  }
+  T("image backdrop shows through empty pixels", ok && checked > 100, checked + " empty px checked");
+}
+
+/* 4 eraseMask ----------------------------------------------------------*/
+{
+  const obs = [[0, 0, 0, .05, .05, 3, 0, 1, 0, 0], [0.09, 0, 0, .05, .05, 3, 0, 1, 0, 0],
+               [0.3, 0.3, 0, .05, .05, 3, 0, 1, 0, 0]];
+  const m = SC.eraseMask(obs, 0, 0, 0.12, null);
+  T("brush circle membership", m[0] === true && m[1] === true && m[2] === false);
+  const m2 = SC.eraseMask(obs, 0, 0, 0.12, i => i === 1);
+  T("skip veto respected", m2[0] === true && m2[1] === false && m2[2] === false);
+}
+
+/* 5 erase -> undo round trip (order-free re-append) --------------------*/
+{
+  const obs = randAtoms(60);
+  const before = C.renderPre(obs, H);
+  const mask = SC.eraseMask(obs, 0.1, -0.1, 0.35, null);
+  const removed = [], kept = [];
+  for (let i = 0; i < obs.length; i++) (mask[i] ? removed : kept).push(obs[i]);
+  T("stroke removed something and kept something",
+    removed.length > 0 && kept.length > 0, removed.length + " erased / " + kept.length + " kept");
+  const mid = C.renderPre(kept, H);
+  let changed = 0; for (let i = 0; i < mid.length; i++) if (mid[i] !== before[i]) changed++;
+  T("erase changes the rendered field", changed > 0, changed + " px");
+  const after = C.renderPre(kept.concat(removed), H);   // undo = append at the end
+  let maxd = 0; for (let i = 0; i < after.length; i++) maxd = Math.max(maxd, Math.abs(after[i] - before[i]));
+  T("undo restores the field exactly (order-free)", maxd < 1e-6, "max delta " + maxd.toExponential(1));
+}
+
+/* 6 burn-to-template ----------------------------------------------------*/
+{
+  const template = randAtoms(30);
+  // scene build records src by REFERENCE, like the studio does
+  const src = template.map(ref => ({ li: 0, ref }));
+  const layer = { template: template.slice() };
+  const mask = SC.eraseMask(template, 0, 0, 0.4, null);
+  const burned = [];
+  for (let i = 0; i < template.length; i++) if (mask[i]) {
+    const idx = layer.template.indexOf(src[i].ref);
+    if (idx >= 0) { layer.template.splice(idx, 1); burned.push(src[i]); }
+  }
+  const nGone = mask.filter(Boolean).length;
+  T("burn removes exactly the erased refs", burned.length === nGone &&
+    layer.template.length === 30 - nGone, nGone + " burned");
+  T("burned refs really left the template",
+    burned.every(b => !layer.template.includes(b.ref)));
+  for (const b of burned) layer.template.push(b.ref);   // undo
+  T("undo restores template membership", layer.template.length === 30 &&
+    burned.every(b => layer.template.includes(b.ref)));
+}
+
+console.log("\n" + go + " GO, " + fail + " FAIL");
+process.exit(fail ? 1 : 0);