Group calling: add overflow area

ts/test-both/helpers/fakeGetGroupCallVideoFrameSource.ts

@@ -0,0 +1,62 @@
+// Copyright 2021 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+import { VideoFrameSource } from '../../types/Calling';
+
+const COLORS: Array<[number, number, number]> = [
+  [0xff, 0x00, 0x00],
+  [0xff, 0x99, 0x00],
+  [0xff, 0xff, 0x00],
+  [0x00, 0xff, 0x00],
+  [0x00, 0x99, 0xff],
+  [0xff, 0x00, 0xff],
+  [0x99, 0x33, 0xff],
+];
+
+class FakeGroupCallVideoFrameSource implements VideoFrameSource {
+  private readonly sourceArray: Uint8Array;
+
+  private readonly dimensions: [number, number];
+
+  constructor(width: number, height: number, r: number, g: number, b: number) {
+    const length = width * height * 4;
+
+    this.sourceArray = new Uint8Array(length);
+    for (let i = 0; i < length; i += 4) {
+      this.sourceArray[i] = r;
+      this.sourceArray[i + 1] = g;
+      this.sourceArray[i + 2] = b;
+      this.sourceArray[i + 3] = 255;
+    }
+
+    this.dimensions = [width, height];
+  }
+
+  receiveVideoFrame(
+    destinationBuffer: ArrayBuffer
+  ): [number, number] | undefined {
+    // Simulate network jitter. Also improves performance when testing.
+    if (Math.random() < 0.5) {
+      return undefined;
+    }
+
+    new Uint8Array(destinationBuffer).set(this.sourceArray);
+    return this.dimensions;
+  }
+}
+
+/**
+ * This produces a fake video frame source that is a single color.
+ *
+ * The aspect ratio is fixed at 1.3 because that matches many of our stories.
+ */
+export function fakeGetGroupCallVideoFrameSource(
+  demuxId: number
+): VideoFrameSource {
+  const color = COLORS[demuxId % COLORS.length];
+  if (!color) {
+    throw new Error('Expected a color, but it was not found');
+  }
+  const [r, g, b] = color;
+
+  return new FakeGroupCallVideoFrameSource(13, 10, r, g, b);
+}