Segregate script canvas context

src/main/resources/static/css/styles.css

@@ -1120,10 +1120,22 @@ button:disabled:hover {
     z-index: 1;
 }
 
-#broadcast-script-canvas {
+.broadcast-script-layer {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    pointer-events: none;
     z-index: 2;
 }
 
+.broadcast-script-layer canvas {
+    position: absolute;
+    top: 0;
+    left: 0;
+}
+
 .broadcast-body {
     margin: 0;
     overflow: hidden;

src/main/resources/static/js/broadcast.js

@@ -1,7 +1,7 @@
 import { BroadcastRenderer } from "./broadcast/renderer.js";
 
 const canvas = document.getElementById("broadcast-canvas");
-const scriptCanvas = document.getElementById("broadcast-script-canvas");
+const scriptLayer = document.getElementById("broadcast-script-layer");
-const renderer = new BroadcastRenderer({ canvas, scriptCanvas, broadcaster, showToast });
+const renderer = new BroadcastRenderer({ canvas, scriptLayer, broadcaster, showToast });
 
 renderer.start();

src/main/resources/static/js/broadcast/renderer.js

@@ -8,10 +8,11 @@ import { createMediaManager } from "./mediaManager.js";
 import { createModelManager } from "../media/modelManager.js";
 
 export class BroadcastRenderer {
-    constructor({ canvas, scriptCanvas, broadcaster, showToast }) {
+    constructor({ canvas, scriptLayer, broadcaster, showToast }) {
         this.canvas = canvas;
         this.ctx = canvas.getContext("2d");
-        this.scriptCanvas = scriptCanvas;
+        this.scriptLayer = scriptLayer;
+        this.scriptCanvases = new Map();
         this.broadcaster = broadcaster;
         this.showToast = showToast;
         this.state = createBroadcastState();
@@ -146,13 +147,12 @@ export class BroadcastRenderer {
             this.canvas.height = this.state.canvasSettings.height;
             this.canvas.style.width = `${this.state.canvasSettings.width}px`;
             this.canvas.style.height = `${this.state.canvasSettings.height}px`;
-            if (this.scriptCanvas) {
+            if (this.scriptLayer) {
-                this.scriptCanvas.width = this.state.canvasSettings.width;
+                this.scriptLayer.style.width = `${this.state.canvasSettings.width}px`;
-                this.scriptCanvas.height = this.state.canvasSettings.height;
+                this.scriptLayer.style.height = `${this.state.canvasSettings.height}px`;
-                this.scriptCanvas.style.width = `${this.state.canvasSettings.width}px`;
-                this.scriptCanvas.style.height = `${this.state.canvasSettings.height}px`;
             }
         }
+        this.resizeScriptCanvases();
         this.updateScriptWorkerCanvas();
         this.draw();
     }
@@ -395,40 +395,31 @@ export class BroadcastRenderer {
     }
 
     ensureScriptWorker() {
-        if (this.scriptWorker || !this.scriptCanvas) {
+        if (this.scriptWorker) {
             return;
         }
-        if (typeof this.scriptCanvas.transferControlToOffscreen !== "function") {
-            console.warn("OffscreenCanvas is not supported in this environment.");
-            return;
-        }
-        const offscreen = this.scriptCanvas.transferControlToOffscreen();
         this.scriptWorker = new Worker("/js/broadcast/script-worker.js");
         this.scriptWorker.addEventListener("message", (event) => this.handleScriptWorkerMessage(event));
         this.scriptWorker.postMessage(
             {
                 type: "init",
                 payload: {
-                    canvas: offscreen,
-                    width: this.scriptCanvas.width,
-                    height: this.scriptCanvas.height,
                     channelName: this.broadcaster,
                 },
             },
-            [offscreen],
         );
         this.scriptWorkerReady = true;
     }
 
     updateScriptWorkerCanvas() {
-        if (!this.scriptWorker || !this.scriptWorkerReady || !this.scriptCanvas) {
+        if (!this.scriptWorker || !this.scriptWorkerReady) {
             return;
         }
         this.scriptWorker.postMessage({
             type: "resize",
             payload: {
-                width: this.scriptCanvas.width,
+                width: this.state.canvasSettings.width,
-                height: this.scriptCanvas.height,
+                height: this.state.canvasSettings.height,
             },
         });
     }
@@ -483,6 +474,15 @@ export class BroadcastRenderer {
         if (!this.scriptWorkerReady) {
             return;
         }
+        const scriptCanvas = this.ensureScriptCanvas(asset.id);
+        if (!scriptCanvas) {
+            return;
+        }
+        if (typeof scriptCanvas.transferControlToOffscreen !== "function") {
+            console.warn("OffscreenCanvas is not supported in this environment.");
+            return;
+        }
+        const offscreen = scriptCanvas.transferControlToOffscreen();
         let assetSource;
         try {
             const response = await fetch(asset.url);
@@ -499,9 +499,12 @@ export class BroadcastRenderer {
             payload: {
                 id: asset.id,
                 source: assetSource,
+                canvas: offscreen,
+                width: scriptCanvas.width,
+                height: scriptCanvas.height,
                 attachments: await this.resolveScriptAttachments(asset.scriptAttachments),
             },
-        });
+        }, [offscreen]);
     }
 
     async updateScriptWorkerAttachments(asset) {
@@ -525,6 +528,53 @@ export class BroadcastRenderer {
             type: "removeScript",
             payload: { id: assetId },
         });
+        this.removeScriptCanvas(assetId);
+    }
+
+    ensureScriptCanvas(assetId) {
+        if (!assetId || !this.scriptLayer) {
+            return null;
+        }
+        const existing = this.scriptCanvases.get(assetId);
+        if (existing) {
+            return existing;
+        }
+        const canvas = document.createElement("canvas");
+        canvas.className = "broadcast-script-canvas";
+        canvas.dataset.scriptId = assetId;
+        this.applyScriptCanvasSize(canvas);
+        this.scriptLayer.appendChild(canvas);
+        this.scriptCanvases.set(assetId, canvas);
+        return canvas;
+    }
+
+    removeScriptCanvas(assetId) {
+        const canvas = this.scriptCanvases.get(assetId);
+        if (!canvas) {
+            return;
+        }
+        canvas.remove();
+        this.scriptCanvases.delete(assetId);
+    }
+
+    resizeScriptCanvases() {
+        this.scriptCanvases.forEach((canvas) => {
+            this.applyScriptCanvasSize(canvas);
+        });
+    }
+
+    applyScriptCanvasSize(canvas) {
+        if (!canvas) {
+            return;
+        }
+        if (Number.isFinite(this.state.canvasSettings.width)) {
+            canvas.width = this.state.canvasSettings.width;
+            canvas.style.width = `${this.state.canvasSettings.width}px`;
+        }
+        if (Number.isFinite(this.state.canvasSettings.height)) {
+            canvas.height = this.state.canvasSettings.height;
+            canvas.style.height = `${this.state.canvasSettings.height}px`;
+        }
     }
 
     async resolveScriptAttachments(attachments) {

src/main/resources/static/js/broadcast/script-worker.js

@@ -1,7 +1,5 @@
 const scripts = new Map();
 const allowedFetchUrls = new Set();
-let canvas = null;
-let ctx = null;
 let channelName = "";
 let tickIntervalId = null;
 let lastTick = 0;
@@ -134,11 +132,11 @@ function updateScriptContexts() {
         if (!script.context) {
             return;
         }
-        script.context.canvas = canvas;
+        script.context.canvas = script.canvas;
-        script.context.ctx = ctx;
+        script.context.ctx = script.ctx;
         script.context.channelName = channelName;
-        script.context.width = canvas?.width ?? 0;
+        script.context.width = script.canvas?.width ?? 0;
-        script.context.height = canvas?.height ?? 0;
+        script.context.height = script.canvas?.height ?? 0;
     });
 }
 
@@ -149,7 +147,7 @@ function ensureTickLoop() {
     startTime = performance.now();
     lastTick = startTime;
     tickIntervalId = setInterval(() => {
-        if (!ctx || scripts.size === 0) {
+        if (scripts.size === 0) {
             return;
         }
         const now = performance.now();
@@ -158,7 +156,7 @@ function ensureTickLoop() {
         lastTick = now;
 
         scripts.forEach((script) => {
-            if (!script.tick) {
+            if (!script.tick || !script.ctx) {
                 return;
             }
             script.context.now = now;
@@ -199,22 +197,19 @@ function createScriptHandlers(source, context, state, sourceLabel = "") {
 self.addEventListener("message", (event) => {
     const { type, payload } = event.data || {};
     if (type === "init") {
-        canvas = payload.canvas;
         channelName = payload.channelName || "";
-        if (canvas) {
-            canvas.width = payload.width || canvas.width;
-            canvas.height = payload.height || canvas.height;
-            ctx = canvas.getContext("2d");
-        }
         updateScriptContexts();
         return;
     }
 
     if (type === "resize") {
-        if (canvas) {
+        scripts.forEach((script) => {
-            canvas.width = payload.width || canvas.width;
+            if (!script.canvas) {
-            canvas.height = payload.height || canvas.height;
+                return;
-        }
+            }
+            script.canvas.width = payload.width || script.canvas.width;
+            script.canvas.height = payload.height || script.canvas.height;
+        });
         updateScriptContexts();
         return;
     }
@@ -226,16 +221,20 @@ self.addEventListener("message", (event) => {
     }
 
     if (type === "addScript") {
-        if (!payload?.id || !payload?.source) {
+        if (!payload?.id || !payload?.source || !payload?.canvas) {
             return;
         }
+        const canvas = payload.canvas;
+        canvas.width = payload.width || canvas.width;
+        canvas.height = payload.height || canvas.height;
+        const ctx = canvas.getContext("2d");
         const state = {};
         const context = {
             canvas,
             ctx,
             channelName,
-            width: canvas?.width ?? 0,
+            width: canvas.width ?? 0,
-            height: canvas?.height ?? 0,
+            height: canvas.height ?? 0,
             now: 0,
             deltaMs: 0,
             elapsedMs: 0,
@@ -251,6 +250,8 @@ self.addEventListener("message", (event) => {
         }
         const script = {
             id: payload.id,
+            canvas,
+            ctx,
             context,
             state,
             init: handlers.init,

src/main/resources/templates/broadcast.html

@@ -13,7 +13,7 @@
     </head>
     <body class="broadcast-body">
         <canvas id="broadcast-canvas"></canvas>
-        <canvas id="broadcast-script-canvas"></canvas>
+        <div id="broadcast-script-layer" class="broadcast-script-layer"></div>
         <script th:inline="javascript">
             const broadcaster = /*[[${broadcaster}]]*/ "";
         </script>