refactor: move spec helpers to spec/lib (#37010)

Co-authored-by: Milan Burda <miburda@microsoft.com>

spec/lib/screen-helpers.ts

@@ -0,0 +1,92 @@
+import * as path from 'path';
+import * as fs from 'fs';
+import { screen, desktopCapturer, NativeImage } from 'electron';
+
+const fixtures = path.resolve(__dirname, '..', 'fixtures');
+
+export enum HexColors {
+  GREEN = '#00b140',
+  PURPLE = '#6a0dad',
+  RED = '#ff0000',
+  BLUE = '#0000ff'
+};
+
+/**
+ * Capture the screen at the given point.
+ *
+ * NOTE: Not yet supported on Linux in CI due to empty sources list.
+ */
+export const captureScreen = async (point: Electron.Point = { x: 0, y: 0 }): Promise<NativeImage> => {
+  const display = screen.getDisplayNearestPoint(point);
+  const sources = await desktopCapturer.getSources({ types: ['screen'], thumbnailSize: display.size });
+  // Toggle to save screen captures for debugging.
+  const DEBUG_CAPTURE = process.env.DEBUG_CAPTURE || false;
+  if (DEBUG_CAPTURE) {
+    for (const source of sources) {
+      await fs.promises.writeFile(path.join(fixtures, `screenshot_${source.display_id}_${Date.now()}.png`), source.thumbnail.toPNG());
+    }
+  }
+  const screenCapture = sources.find(source => source.display_id === `${display.id}`);
+  // Fails when HDR is enabled on Windows.
+  // https://bugs.chromium.org/p/chromium/issues/detail?id=1247730
+  if (!screenCapture) {
+    const displayIds = sources.map(source => source.display_id);
+    throw new Error(`Unable to find screen capture for display '${display.id}'\n\tAvailable displays: ${displayIds.join(', ')}`);
+  }
+  return screenCapture.thumbnail;
+};
+
+const formatHexByte = (val: number): string => {
+  const str = val.toString(16);
+  return str.length === 2 ? str : `0${str}`;
+};
+
+/**
+ * Get the hex color at the given pixel coordinate in an image.
+ */
+export const getPixelColor = (image: Electron.NativeImage, point: Electron.Point): string => {
+  // image.crop crashes if point is fractional, so round to prevent that crash
+  const pixel = image.crop({ x: Math.round(point.x), y: Math.round(point.y), width: 1, height: 1 });
+  // TODO(samuelmaddock): NativeImage.toBitmap() should return the raw pixel
+  // color, but it sometimes differs. Why is that?
+  const [b, g, r] = pixel.toBitmap();
+  return `#${formatHexByte(r)}${formatHexByte(g)}${formatHexByte(b)}`;
+};
+
+const hexToRgba = (hexColor: string) => {
+  const match = hexColor.match(/^#([0-9a-fA-F]{6,8})$/);
+  if (!match) return;
+
+  const colorStr = match[1];
+  return [
+    parseInt(colorStr.substring(0, 2), 16),
+    parseInt(colorStr.substring(2, 4), 16),
+    parseInt(colorStr.substring(4, 6), 16),
+    parseInt(colorStr.substring(6, 8), 16) || 0xFF
+  ];
+};
+
+/** Calculate euclidian distance between colors. */
+const colorDistance = (hexColorA: string, hexColorB: string) => {
+  const colorA = hexToRgba(hexColorA);
+  const colorB = hexToRgba(hexColorB);
+  if (!colorA || !colorB) return -1;
+  return Math.sqrt(
+    Math.pow(colorB[0] - colorA[0], 2) +
+    Math.pow(colorB[1] - colorA[1], 2) +
+    Math.pow(colorB[2] - colorA[2], 2)
+  );
+};
+
+/**
+ * Determine if colors are similar based on distance. This can be useful when
+ * comparing colors which may differ based on lossy compression.
+ */
+export const areColorsSimilar = (
+  hexColorA: string,
+  hexColorB: string,
+  distanceThreshold = 90
+): boolean => {
+  const distance = colorDistance(hexColorA, hexColorB);
+  return distance <= distanceThreshold;
+};