snapshot of https://github.com/jitsi/jitsi-meet.git @ fd1749dd28f4138aa80234fc7f311b19aaffa0e7 (2026-09-15)

react/features/screenshot-capture/worker.ts

@@ -0,0 +1,132 @@
+import pixelmatch from 'pixelmatch';
+
+import {
+    CLEAR_TIMEOUT,
+    MAX_FILE_SIZE,
+    PERCENTAGE_LOWER_BOUND,
+    SET_TIMEOUT,
+    TIMEOUT_TICK
+} from './constants';
+
+
+let timer: ReturnType<typeof setTimeout>;
+const canvas = new OffscreenCanvas(0, 0);
+const ctx = canvas.getContext('2d');
+let storedImageData: ImageData | undefined;
+
+/**
+ * Sends Blob with the screenshot to main thread.
+ *
+  * @param {ImageData} imageData - The image of the screenshot.
+ * @returns {void}
+ */
+async function sendBlob(imageData: ImageData) {
+    let imageBlob = await canvas.convertToBlob({ type: 'image/jpeg' });
+
+    if (imageBlob.size > MAX_FILE_SIZE) {
+        const quality = Number((MAX_FILE_SIZE / imageBlob.size).toFixed(2)) * 0.92;
+
+        imageBlob = await canvas.convertToBlob({ type: 'image/jpeg',
+            quality });
+    }
+
+    storedImageData = imageData;
+
+    postMessage({
+        id: TIMEOUT_TICK,
+        imageBlob
+    });
+}
+
+/**
+ * Sends empty message to main thread.
+ *
+ * @returns {void}
+ */
+function sendEmpty() {
+    postMessage({
+        id: TIMEOUT_TICK
+    });
+}
+
+/**
+ * Draws the image bitmap on the canvas and checks the difference percent with the previous image
+ * if there is no previous image the percentage is not calculated.
+ *
+ * @param {ImageBitmap} imageBitmap - The image bitmap that is drawn on canvas.
+ * @returns {void}
+ */
+function checkScreenshot(imageBitmap: ImageBitmap) {
+    const { height, width } = imageBitmap;
+
+    if (canvas.width !== width) {
+        canvas.width = width;
+    }
+
+    if (canvas.height !== height) {
+        canvas.height = height;
+    }
+
+    ctx?.drawImage(imageBitmap, 0, 0, width, height);
+    const imageData = ctx?.getImageData(0, 0, width, height);
+
+    imageBitmap.close();
+
+    if (!imageData) {
+        sendEmpty();
+
+        return;
+    }
+
+    if (!storedImageData || imageData.data.length !== storedImageData.data.length) {
+        sendBlob(imageData);
+
+        return;
+    }
+
+    let numOfPixels = 0;
+
+    try {
+        numOfPixels = pixelmatch(
+            imageData.data,
+            storedImageData.data,
+            null,
+            width,
+            height);
+    } catch {
+        sendEmpty();
+
+        return;
+    }
+
+    const percent = numOfPixels / imageData.data.length * 100;
+
+    if (percent >= PERCENTAGE_LOWER_BOUND) {
+        sendBlob(imageData);
+    } else {
+        sendEmpty();
+    }
+}
+
+onmessage = function(request) {
+    switch (request.data.id) {
+    case SET_TIMEOUT: {
+        timer = setTimeout(async () => {
+            const imageBitmap = request.data.imageBitmap;
+
+            if (imageBitmap) {
+                checkScreenshot(imageBitmap);
+            } else {
+                sendEmpty();
+            }
+        }, request.data.timeMs);
+        break;
+    }
+    case CLEAR_TIMEOUT: {
+        if (timer) {
+            clearTimeout(timer);
+        }
+        break;
+    }
+    }
+};