fix(ssim-cie94): make sure a single off pixel yields diff in comparator (#24348)

This patch brings in antialiasing tests from `looks-same` project for
our experimental `ssim-cie94` comparator.

One of the new tests found a bug in our implementation.

References https://github.com/microsoft/playwright/issues/24312

packages/playwright-core/src/image_tools/compare.ts

@@ -86,8 +86,6 @@ export function compare(actual: Buffer, expected: Buffer, diff: Buffer|null, wid
         continue;
       }
 
-      // if this pixel is a part of a flood fill of a 3x3 square then it cannot be
-      // anti-aliasing pixel so it must be a pixel difference.
       if (!fastR || !fastG || !fastB) {
         fastR = new FastStats(r1, r2);
         fastG = new FastStats(g1, g2);
@@ -97,7 +95,9 @@ export function compare(actual: Buffer, expected: Buffer, diff: Buffer|null, wid
       const [varX2, varY2] = r1.boundXY(x + VARIANCE_WINDOW_RADIUS, y + VARIANCE_WINDOW_RADIUS);
       const var1 = fastR.varianceC1(varX1, varY1, varX2, varY2) + fastG.varianceC1(varX1, varY1, varX2, varY2) + fastB.varianceC1(varX1, varY1, varX2, varY2);
       const var2 = fastR.varianceC2(varX1, varY1, varX2, varY2) + fastG.varianceC2(varX1, varY1, varX2, varY2) + fastB.varianceC2(varX1, varY1, varX2, varY2);
-      if (var1 === 0 && var2 === 0) {
+      // if this pixel is a part of a flood fill of a 3x3 square of either of the images, then it cannot be
+      // anti-aliasing pixel so it must be a pixel difference.
+      if (var1 === 0 || var2 === 0) {
         drawRedPixel(x, y);
         ++diffCount;
         continue;

tests/image_tools/fixtures/should-fail/looks-same-tests/README.md

@@ -0,0 +1,2 @@
+These tests are coming from the `looks-same` library:
+- https://github.com/gemini-testing/looks-same/blob/b9399bce8fd980e6e59cf740bee3cd3fe66c3eae/test/test.js

tests/image_tools/fixtures/should-match/looks-same-tests/README.md

@@ -0,0 +1,2 @@
+These tests are coming from the `looks-same` library:
+- https://github.com/gemini-testing/looks-same/blob/b9399bce8fd980e6e59cf740bee3cd3fe66c3eae/test/test.js