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diff --git a/public/bluebey-studio/src/occlusion.js b/public/bluebey-studio/src/occlusion.js
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+++ b/public/bluebey-studio/src/occlusion.js
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+// src/occlusion.js
+//
+// A tiny "hide ぶるべー behind this" mask editor.
+//
+// WHY: the background is a fixed image, so hiding the character behind a tree
+// is a 2D masking job, not a depth-estimation one. The user taps the object;
+// a magic wand (see floodfill.js) marks it. The editor hands back two PNGs:
+//
+//   mask    - opaque where the object is, used by the export to punch the
+//             character out there (`destination-out`)
+//   inverse - transparent where the object is, used as a CSS `mask-image` on
+//             the WebGL canvas so the live preview hides it too
+//
+// Both are in the canvas' CSS pixel space, so the editor is handed the
+// backdrop *as already painted* (fit, scale, offset, blur, darken applied by
+// main.js) rather than the raw photo. That keeps the mask aligned with what
+// the export will draw.
+
+import { floodFill } from './floodfill.js';
+
+const DEFAULT_TOLERANCE = 32;
+
+/**
+ * @param {HTMLCanvasElement} backdrop the backdrop painted at the canvas' CSS
+ *   size (the same pixels the export will composite)
+ * @param {HTMLCanvasElement|null} character a transparent-background render of
+ *   the character, drawn faintly so the user can aim
+ * @param {{ left:number, top:number, width:number, height:number }} rect the
+ *   canvas' on-screen rectangle
+ * @returns {Promise<{mask:string, inverse:string}|null>} null when cancelled
+ */
+export function openOcclusionEditor({ backdrop, character = null, rect }) {
+  return new Promise((resolve) => {
+    const width = Math.max(1, Math.round(rect.width));
+    const height = Math.max(1, Math.round(rect.height));
+
+    const root = document.createElement('div');
+    root.className = 'occlusion-editor';
+    root.style.cssText = [
+      'position:fixed',
+      `left:${rect.left}px`,
+      `top:${rect.top}px`,
+      `width:${width}px`,
+      `height:${height}px`,
+      'z-index:100',
+      'background:#111',
+      'overflow:hidden',
+      'touch-action:none',
+      'user-select:none',
+      'font:13px system-ui, "Hiragino Sans", "Yu Gothic UI", sans-serif',
+    ].join(';');
+
+    // The backdrop, exactly as the studio paints it.
+    const photo = document.createElement('canvas');
+    photo.width = width;
+    photo.height = height;
+    photo.style.cssText = 'position:absolute;inset:0;width:100%;height:100%;cursor:crosshair;';
+    const pctx = photo.getContext('2d', { willReadFrequently: true });
+    pctx.drawImage(backdrop, 0, 0, width, height);
+    const pixels = pctx.getImageData(0, 0, width, height).data;
+
+    // A faint copy of ぶるべー, so the user can see what is being covered.
+    const ghost = document.createElement('canvas');
+    ghost.width = width;
+    ghost.height = height;
+    ghost.style.cssText = 'position:absolute;inset:0;width:100%;height:100%;opacity:0.55;pointer-events:none;';
+    if (character) ghost.getContext('2d').drawImage(character, 0, 0, width, height);
+
+    // The mask: opaque white where the object is.
+    const mask = document.createElement('canvas');
+    mask.width = width;
+    mask.height = height;
+    mask.style.cssText = 'position:absolute;inset:0;width:100%;height:100%;opacity:0.55;pointer-events:none;';
+    const mctx = mask.getContext('2d');
+    const maskImage = mctx.createImageData(width, height);
+
+    const bar = document.createElement('div');
+    bar.style.cssText = [
+      'position:absolute',
+      'left:0', 'right:0', 'top:0',
+      'display:flex', 'flex-wrap:wrap', 'gap:8px', 'align-items:center',
+      'padding:8px 10px',
+      'background:rgba(20,16,28,0.86)', 'color:#fff',
+      'box-sizing:border-box',
+    ].join(';');
+
+    const title = document.createElement('strong');
+    title.textContent = '隠すマスク';
+
+    const hintText = document.createElement('span');
+    hintText.textContent = '隠したい物（木・建物など）をタップ。何回でも追加できます';
+    hintText.style.cssText = 'opacity:0.8;flex:1 1 220px;';
+
+    const toleranceWrap = document.createElement('label');
+    toleranceWrap.style.cssText = 'display:flex;gap:6px;align-items:center;white-space:nowrap;';
+    toleranceWrap.append(document.createTextNode('にじみ'));
+    const tolerance = document.createElement('input');
+    tolerance.type = 'range';
+    tolerance.min = '0';
+    tolerance.max = '100';
+    tolerance.step = '1';
+    tolerance.value = String(DEFAULT_TOLERANCE);
+    tolerance.style.width = '110px';
+    toleranceWrap.append(tolerance);
+
+    const button = (label, onClick) => {
+      const el = document.createElement('button');
+      el.type = 'button';
+      el.textContent = label;
+      el.style.cssText = 'padding:4px 10px;border:1px solid rgba(255,255,255,0.35);border-radius:6px;background:rgba(255,255,255,0.1);color:#fff;cursor:pointer;';
+      el.addEventListener('click', onClick);
+      return el;
+    };
+
+    const undoStack = [];
+
+    bar.append(
+      title,
+      hintText,
+      toleranceWrap,
+      button('クリア', () => {
+        undoStack.length = 0;
+        maskImage.data.fill(0);
+        mctx.putImageData(maskImage, 0, 0);
+      }),
+      button('キャンセル', () => { cleanup(); resolve(null); }),
+      button('決定', () => {
+        cleanup();
+        resolve({ mask: mask.toDataURL('image/png'), inverse: invertedDataUrl(mask, width, height) });
+      }),
+    );
+
+    root.append(photo, ghost, mask, bar);
+    document.body.append(root);
+
+    function cleanup() {
+      root.remove();
+      window.removeEventListener('keydown', onKeydown);
+    }
+
+    /** @param {string} dataUrl */
+    function invertedDataUrl(source, w, h) {
+      const out = document.createElement('canvas');
+      out.width = w;
+      out.height = h;
+      const ctx = out.getContext('2d');
+      ctx.fillStyle = '#fff';
+      ctx.fillRect(0, 0, w, h);
+      ctx.globalCompositeOperation = 'destination-out';
+      ctx.drawImage(source, 0, 0);
+      return out.toDataURL('image/png');
+    }
+
+    photo.addEventListener('pointerdown', (event) => {
+      if (event.button !== 0) return;
+      const r = photo.getBoundingClientRect();
+      const before = new Uint8ClampedArray(maskImage.data);
+      const count = floodFill({
+        pixels,
+        mask: maskImage.data,
+        width,
+        height,
+        x: event.clientX - r.left,
+        y: event.clientY - r.top,
+        tolerance: Number(tolerance.value),
+      });
+      if (!count) return;
+      undoStack.push(before);
+      if (undoStack.length > 5) undoStack.shift();
+      mctx.putImageData(maskImage, 0, 0);
+    });
+
+    // Ctrl/⌘+Z takes back the last tap, which is the mistake people make most.
+    function onKeydown(event) {
+      if (!(event.ctrlKey || event.metaKey) || event.key.toLowerCase() !== 'z') return;
+      const before = undoStack.pop();
+      if (!before) return;
+      maskImage.data.set(before);
+      mctx.putImageData(maskImage, 0, 0);
+      event.preventDefault();
+    }
+    window.addEventListener('keydown', onKeydown);
+  });
+}