perf(canvas): port renderer to PixiJS (GPU pan/zoom) + cap DPR at 2

Replace Canvas2D render path with pixi.js v8. Canvas stays authored
as CPU RGBA on an OffscreenCanvas; pixi uses that as a texture source
and uploads on demand. Pan/zoom become pure GPU transforms on a
Container — no CPU work per frame. Overlay is a second sprite in the
same container so it tracks pan/zoom for free.

Key points:
- app.ticker.stop() + manual app.renderer.render() on rAF: idle frames
  cost 0, active frames cost one GPU draw.
- mainTexture.source.update() called only when imageDataDirty (same
  gating as before). Writes stay cheap.
- resolution: Math.min(devicePixelRatio, 2). iPhone 3x → 2x = 44%
  fewer fragments; pixel art gains nothing from 3x.
- Public API preserved: applyUpdates, undo/redo, setOverlay, panBy,
  gotoPoint, getCommittedColor, getPendingPixels, commitPending,
  refetchCanvas, cancelStrokeIfAny all unchanged.
- Overlay sprite rebuilt on setOverlay() with destroy({texture,
  textureSource}) to avoid GPU leaks.

Bundle: +200KB main, +~100KB pixi chunks, ~70KB gz total. Tradeoff
accepted for mobile perf parity with wplace.

package-lock.json

@@ -7,7 +7,8 @@
       "name": "rplace",
       "dependencies": {
         "@upstash/redis": "^1.34.3",
-        "hono": "^4.7.6"
+        "hono": "^4.7.6",
+        "pixi.js": "^8.18.1"
       },
       "devDependencies": {
         "@sveltejs/vite-plugin-svelte": "^5.0.3",
@@ -1252,6 +1253,12 @@
         "debug": "^4.1.1"
       }
     },
+    "node_modules/@pixi/colord": {
+      "version": "2.9.6",
+      "resolved": "https://registry.npmjs.org/@pixi/colord/-/colord-2.9.6.tgz",
+      "integrity": "sha512-nezytU2pw587fQstUu1AsJZDVEynjskwOL+kibwcdxsMBFqPsFFNA7xl0ii/gXuDi6M0xj3mfRJj8pBSc2jCfA==",
+      "license": "MIT"
+    },
     "node_modules/@pkgjs/parseargs": {
       "version": "0.11.0",
       "resolved": "https://registry.npmjs.org/@pkgjs/parseargs/-/parseargs-0.11.0.tgz",
@@ -1834,6 +1841,12 @@
         "@types/ssh2": "*"
       }
     },
+    "node_modules/@types/earcut": {
+      "version": "3.0.0",
+      "resolved": "https://registry.npmjs.org/@types/earcut/-/earcut-3.0.0.tgz",
+      "integrity": "sha512-k/9fOUGO39yd2sCjrbAJvGDEQvRwRnQIZlBz43roGwUZo5SHAmyVvSFyaVVZkicRVCaDXPKlbxrUcBuJoSWunQ==",
+      "license": "MIT"
+    },
     "node_modules/@types/estree": {
       "version": "1.0.8",
       "resolved": "https://registry.npmjs.org/@types/estree/-/estree-1.0.8.tgz",
@@ -2017,6 +2030,21 @@
         "url": "https://opencollective.com/vitest"
       }
     },
+    "node_modules/@webgpu/types": {
+      "version": "0.1.69",
+      "resolved": "https://registry.npmjs.org/@webgpu/types/-/types-0.1.69.tgz",
+      "integrity": "sha512-RPmm6kgRbI8e98zSD3RVACvnuktIja5+yLgDAkTmxLr90BEwdTXRQWNLF3ETTTyH/8mKhznZuN5AveXYFEsMGQ==",
+      "license": "BSD-3-Clause"
+    },
+    "node_modules/@xmldom/xmldom": {
+      "version": "0.8.12",
+      "resolved": "https://registry.npmjs.org/@xmldom/xmldom/-/xmldom-0.8.12.tgz",
+      "integrity": "sha512-9k/gHF6n/pAi/9tqr3m3aqkuiNosYTurLLUtc7xQ9sxB/wm7WPygCv8GYa6mS0fLJEHhqMC1ATYhz++U/lRHqg==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=10.0.0"
+      }
+    },
     "node_modules/abort-controller": {
       "version": "3.0.0",
       "resolved": "https://registry.npmjs.org/abort-controller/-/abort-controller-3.0.0.tgz",
@@ -2851,6 +2879,12 @@
         "node": ">=6"
       }
     },
+    "node_modules/earcut": {
+      "version": "3.0.2",
+      "resolved": "https://registry.npmjs.org/earcut/-/earcut-3.0.2.tgz",
+      "integrity": "sha512-X7hshQbLyMJ/3RPhyObLARM2sNxxmRALLKx1+NVFFnQ9gKzmCrxm9+uLIAdBcvc8FNLpctqlQ2V6AE92Ol9UDQ==",
+      "license": "ISC"
+    },
     "node_modules/eastasianwidth": {
       "version": "0.2.0",
       "resolved": "https://registry.npmjs.org/eastasianwidth/-/eastasianwidth-0.2.0.tgz",
@@ -2989,6 +3023,12 @@
         "node": ">=6"
       }
     },
+    "node_modules/eventemitter3": {
+      "version": "5.0.4",
+      "resolved": "https://registry.npmjs.org/eventemitter3/-/eventemitter3-5.0.4.tgz",
+      "integrity": "sha512-mlsTRyGaPBjPedk6Bvw+aqbsXDtoAyAzm5MO7JgU+yVRyMQ5O8bD4Kcci7BS85f93veegeCPkL8R4GLClnjLFw==",
+      "license": "MIT"
+    },
     "node_modules/events": {
       "version": "3.3.0",
       "resolved": "https://registry.npmjs.org/events/-/events-3.3.0.tgz",
@@ -3106,6 +3146,15 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/gifuct-js": {
+      "version": "2.1.2",
+      "resolved": "https://registry.npmjs.org/gifuct-js/-/gifuct-js-2.1.2.tgz",
+      "integrity": "sha512-rI2asw77u0mGgwhV3qA+OEgYqaDn5UNqgs+Bx0FGwSpuqfYn+Ir6RQY5ENNQ8SbIiG/m5gVa7CD5RriO4f4Lsg==",
+      "license": "MIT",
+      "dependencies": {
+        "js-binary-schema-parser": "^2.0.3"
+      }
+    },
     "node_modules/glob": {
       "version": "10.5.0",
       "resolved": "https://registry.npmjs.org/glob/-/glob-10.5.0.tgz",
@@ -3244,6 +3293,12 @@
       "dev": true,
       "license": "ISC"
     },
+    "node_modules/ismobilejs": {
+      "version": "1.1.1",
+      "resolved": "https://registry.npmjs.org/ismobilejs/-/ismobilejs-1.1.1.tgz",
+      "integrity": "sha512-VaFW53yt8QO61k2WJui0dHf4SlL8lxBofUuUmwBo0ljPk0Drz2TiuDW4jo3wDcv41qy/SxrJ+VAzJ/qYqsmzRw==",
+      "license": "MIT"
+    },
     "node_modules/jackspeak": {
       "version": "3.4.3",
       "resolved": "https://registry.npmjs.org/jackspeak/-/jackspeak-3.4.3.tgz",
@@ -3260,6 +3315,12 @@
         "@pkgjs/parseargs": "^0.11.0"
       }
     },
+    "node_modules/js-binary-schema-parser": {
+      "version": "2.0.3",
+      "resolved": "https://registry.npmjs.org/js-binary-schema-parser/-/js-binary-schema-parser-2.0.3.tgz",
+      "integrity": "sha512-xezGJmOb4lk/M1ZZLTR/jaBHQ4gG/lqQnJqdIv4721DMggsa1bDVlHXNeHYogaIEHD9vCRv0fcL4hMA+Coarkg==",
+      "license": "MIT"
+    },
     "node_modules/kleur": {
       "version": "4.1.5",
       "resolved": "https://registry.npmjs.org/kleur/-/kleur-4.1.5.tgz",
@@ -3527,6 +3588,12 @@
       "dev": true,
       "license": "BlueOak-1.0.0"
     },
+    "node_modules/parse-svg-path": {
+      "version": "0.1.2",
+      "resolved": "https://registry.npmjs.org/parse-svg-path/-/parse-svg-path-0.1.2.tgz",
+      "integrity": "sha512-JyPSBnkTJ0AI8GGJLfMXvKq42cj5c006fnLz6fXy6zfoVjJizi8BNTpu8on8ziI1cKy9d9DGNuY17Ce7wuejpQ==",
+      "license": "MIT"
+    },
     "node_modules/path-key": {
       "version": "3.1.1",
       "resolved": "https://registry.npmjs.org/path-key/-/path-key-3.1.1.tgz",
@@ -3588,6 +3655,32 @@
         "url": "https://github.com/sponsors/jonschlinkert"
       }
     },
+    "node_modules/pixi.js": {
+      "version": "8.18.1",
+      "resolved": "https://registry.npmjs.org/pixi.js/-/pixi.js-8.18.1.tgz",
+      "integrity": "sha512-6LUPWYgulZhp/w4kam2XHXB0QedISZIqrJbRdHLLQ3csn5a38uzKxAp6B5j6s89QFYaIJbg95kvgTRcbgpO1ow==",
+      "license": "MIT",
+      "workspaces": [
+        "examples",
+        "playground"
+      ],
+      "dependencies": {
+        "@pixi/colord": "^2.9.6",
+        "@types/earcut": "^3.0.0",
+        "@webgpu/types": "^0.1.69",
+        "@xmldom/xmldom": "^0.8.12",
+        "earcut": "^3.0.2",
+        "eventemitter3": "^5.0.1",
+        "gifuct-js": "^2.1.2",
+        "ismobilejs": "^1.1.1",
+        "parse-svg-path": "^0.1.2",
+        "tiny-lru": "^11.4.7"
+      },
+      "funding": {
+        "type": "opencollective",
+        "url": "https://opencollective.com/pixijs"
+      }
+    },
     "node_modules/postcss": {
       "version": "8.5.10",
       "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.10.tgz",
@@ -4281,6 +4374,15 @@
         "b4a": "^1.6.4"
       }
     },
+    "node_modules/tiny-lru": {
+      "version": "11.4.7",
+      "resolved": "https://registry.npmjs.org/tiny-lru/-/tiny-lru-11.4.7.tgz",
+      "integrity": "sha512-w/Te7uMUVeH0CR8vZIjr+XiN41V+30lkDdK+NRIDCUYKKuL9VcmaUEmaPISuwGhLlrTGh5yu18lENtR9axSxYw==",
+      "license": "BSD-3-Clause",
+      "engines": {
+        "node": ">=12"
+      }
+    },
     "node_modules/tinybench": {
       "version": "2.9.0",
       "resolved": "https://registry.npmjs.org/tinybench/-/tinybench-2.9.0.tgz",

package.json

@@ -15,7 +15,8 @@
   },
   "dependencies": {
     "@upstash/redis": "^1.34.3",
-    "hono": "^4.7.6"
+    "hono": "^4.7.6",
+    "pixi.js": "^8.18.1"
   },
   "devDependencies": {
     "@sveltejs/vite-plugin-svelte": "^5.0.3",

src/client/components/CanvasRenderer.svelte

@@ -1,5 +1,6 @@
 <script>
   import { onMount } from 'svelte';
+  import { Application, Sprite, Container, Texture } from 'pixi.js';
   import { CANVAS_WIDTH, CANVAS_HEIGHT, COLORS_RGBA, MAX_BATCH_SIZE } from '../../lib/constants.js';
   import { decodeCanvas, indicesToRgba } from '../../lib/canvas-decoder.js';
   import { createPixelBuffer } from '../../lib/pixel-buffer.js';
@@ -24,11 +25,25 @@
   let currentStrokeKeys = new Set();
 
   const buffer = createPixelBuffer();
+
+  // Offscreen canvas holds the "committed+pending" RGBA image. PIXI uses it
+  // as a texture source — we tell PIXI to re-upload when it changes.
   const offscreen = new OffscreenCanvas(CANVAS_WIDTH, CANVAS_HEIGHT);
   const offCtx = offscreen.getContext('2d');
 
-  /** Overlay state: image-importer preview rendered on top of committed+pending.
+  // PIXI state — initialized asynchronously in onMount.
-   *  { x, y, canvas: OffscreenCanvas, alpha } or null. */
+  /** @type {Application|null} */
+  let app = null;
+  /** @type {Container|null} */
+  let worldContainer = null; // holds both sprites; pan via position, zoom via scale
+  /** @type {Sprite|null} */
+  let mainSprite = null;
+  /** @type {Sprite|null} */
+  let overlaySprite = null;
+  /** @type {Texture|null} */
+  let mainTexture = null;
+
+  /** Overlay state mirrored outside of pixi so setOverlay() can defer to init. */
   let overlayState = null;
 
   // Touch state
@@ -36,23 +51,19 @@
   let touchStartTime = 0;
   let touchMoved = false;
 
-  // --- Render coalescing ---
+  // --- Render scheduling ---
-  // Any state change calls render(). Multiple calls within a frame collapse
+  // PIXI's own ticker is stopped; we render manually, coalesced per frame.
-  // to one actual paint via requestAnimationFrame. imageDataDirty gates the
+  // imageDataDirty gates the 16 MB putImageData — only re-upload when pixels
-  // expensive putImageData (16 MB copy): only re-upload when pixels changed.
+  // actually changed (setPixelRgba / loadCanvas).
   let rafPending = false;
   let imageDataDirty = true;
-  let pendingEffZoom = null;
 
-  function render(effZoom = zoom) {
+  function render() {
-    pendingEffZoom = effZoom;
     if (rafPending) return;
     rafPending = true;
     requestAnimationFrame(() => {
       rafPending = false;
-      const z = pendingEffZoom;
+      doRender();
-      pendingEffZoom = null;
-      doRender(z);
     });
   }
 
@@ -72,28 +83,18 @@
     pan.y = Math.max(minY, Math.min(maxY, pan.y));
   }
 
-  function doRender(effZoom) {
+  function doRender() {
-    if (!canvasEl || !imageData) return;
+    if (!app || !worldContainer) return;
-    clampPan(effZoom);
+    clampPan(zoom);
-    const dpr = window.devicePixelRatio || 1;
+    // Flush pixel edits to the offscreen, then tell pixi its texture is stale.
-    const ctx = canvasEl.getContext('2d');
+    if (imageDataDirty && imageData) {
-    ctx.imageSmoothingEnabled = false;
-    ctx.setTransform(1, 0, 0, 1, 0, 0); // reset before clear
-    ctx.fillStyle = '#1a1a1a';
-    ctx.fillRect(0, 0, canvasEl.width, canvasEl.height);
-    if (imageDataDirty) {
       offCtx.putImageData(imageData, 0, 0);
+      mainTexture?.source?.update();
       imageDataDirty = false;
     }
-    ctx.setTransform(dpr, 0, 0, dpr, 0, 0); // CSS pixels → device pixels
+    worldContainer.position.set(pan.x, pan.y);
-    ctx.translate(pan.x, pan.y);
+    worldContainer.scale.set(zoom);
-    ctx.scale(effZoom, effZoom);
+    app.renderer.render(app.stage);
-    ctx.drawImage(offscreen, 0, 0);
-    if (overlayState) {
-      ctx.globalAlpha = overlayState.alpha;
-      ctx.drawImage(overlayState.canvas, overlayState.x, overlayState.y);
-      ctx.globalAlpha = 1;
-    }
   }
 
   function screenToCanvas(clientX, clientY) {
@@ -213,6 +214,12 @@
   /** Set or clear the preview overlay drawn on top of the canvas.
    *  @param {{x: number, y: number, width: number, height: number, indices: Int16Array|number[], alpha?: number}|null} overlay */
   export function setOverlay(overlay) {
+    // Tear down any previous overlay sprite + texture.
+    if (overlaySprite) {
+      worldContainer?.removeChild(overlaySprite);
+      overlaySprite.destroy({ texture: true, textureSource: true });
+      overlaySprite = null;
+    }
     if (!overlay || !overlay.indices || overlay.width <= 0 || overlay.height <= 0) {
       overlayState = null;
       render();
@@ -221,9 +228,16 @@
     const { x, y, width, height, indices, alpha = 0.6 } = overlay;
     const rgba = paletteToRgba(indices, width, height);
     const oc = new OffscreenCanvas(width, height);
-    const octx = oc.getContext('2d');
+    oc.getContext('2d').putImageData(new ImageData(rgba, width, height), 0, 0);
-    octx.putImageData(new ImageData(rgba, width, height), 0, 0);
+    overlayState = { x, y, width, height, canvas: oc, alpha };
-    overlayState = { x, y, canvas: oc, alpha };
+    if (worldContainer) {
+      const tex = Texture.from(oc);
+      tex.source.scaleMode = 'nearest';
+      overlaySprite = new Sprite(tex);
+      overlaySprite.position.set(x, y);
+      overlaySprite.alpha = alpha;
+      worldContainer.addChild(overlaySprite);
+    }
     render();
   }
 
@@ -347,7 +361,7 @@
     pan.x = e.clientX - (e.clientX - pan.x) * (newZoom / zoom);
     pan.y = e.clientY - (e.clientY - pan.y) * (newZoom / zoom);
     if (newZoom !== zoom) onZoomChange(newZoom);
-    render(newZoom); // explicit — covers the case where zoom was clamped
+    render();
   }
 
   // --- Touch handlers ---
@@ -414,7 +428,7 @@
       lastTouchDist = dist;
       lastMouse = center;
       if (newZoom !== zoom) onZoomChange(newZoom);
-      render(newZoom);
+      render();
     }
   }
 
@@ -469,22 +483,86 @@
     }
   }
 
+  async function initPixi() {
+    // Pre-fill the offscreen with a zero-image so the initial texture upload
+    // is valid before loadCanvas() finishes (prevents a one-frame black flash).
+    imageData = new ImageData(
+      new Uint8ClampedArray(CANVAS_WIDTH * CANVAS_HEIGHT * 4),
+      CANVAS_WIDTH, CANVAS_HEIGHT,
+    );
+    offCtx.putImageData(imageData, 0, 0);
+    imageDataDirty = false;
+
+    app = new Application();
+    // Cap DPR at 2 — pixel art gains nothing from 3× and mobile GPUs hate it.
+    const resolution = Math.min(window.devicePixelRatio || 1, 2);
+    await app.init({
+      canvas: canvasEl,
+      width: window.innerWidth,
+      height: window.innerHeight,
+      backgroundColor: 0x1a1a1a,
+      resolution,
+      autoDensity: true,
+      antialias: false,
+    });
+    // Stop auto-ticker — we render on demand (via our rAF coalescer) so idle
+    // frames don't burn GPU cycles.
+    app.ticker.stop();
+
+    mainTexture = Texture.from(offscreen);
+    mainTexture.source.scaleMode = 'nearest';
+    mainSprite = new Sprite(mainTexture);
+
+    worldContainer = new Container();
+    worldContainer.addChild(mainSprite);
+    app.stage.addChild(worldContainer);
+
+    // If an overlay was set before init finished, materialize it now.
+    if (overlayState && !overlaySprite) {
+      const tex = Texture.from(overlayState.canvas);
+      tex.source.scaleMode = 'nearest';
+      overlaySprite = new Sprite(tex);
+      overlaySprite.position.set(overlayState.x, overlayState.y);
+      overlaySprite.alpha = overlayState.alpha;
+      worldContainer.addChild(overlaySprite);
+    }
+  }
+
   onMount(() => {
+    let destroyed = false;
+
     function resize() {
-      const dpr = window.devicePixelRatio || 1;
+      if (!app) return;
-      canvasEl.width = window.innerWidth * dpr;
+      app.renderer.resize(window.innerWidth, window.innerHeight);
-      canvasEl.height = window.innerHeight * dpr;
-      canvasEl.style.width = `${window.innerWidth}px`;
-      canvasEl.style.height = `${window.innerHeight}px`;
       render();
     }
-    resize();
     window.addEventListener('resize', resize);
 
-    // Async load runs in background — onMount cleanup must be sync to avoid leaking listener.
+    // Chain pixi init → initial canvas fetch → first paint.
-    loadCanvas();
+    (async () => {
+      try {
+        await initPixi();
+        if (destroyed) { app?.destroy(false, { children: true, texture: true, textureSource: true }); return; }
+        await loadCanvas();
+        if (destroyed) return;
+        render();
+      } catch (err) {
+        console.error('Renderer init failed:', err);
+        loadError = err.message || String(err);
+      }
+    })();
 
-    return () => window.removeEventListener('resize', resize);
+    return () => {
+      destroyed = true;
+      window.removeEventListener('resize', resize);
+      // `removeView: false` so Svelte keeps managing the <canvas> element.
+      app?.destroy(false, { children: true, texture: true, textureSource: true });
+      app = null;
+      worldContainer = null;
+      mainSprite = null;
+      mainTexture = null;
+      overlaySprite = null;
+    };
   });
 </script>