This reverts commit 303c5998f8b747e94ac80e2e02c53b47ded11322.
Reason for revert: I tried enabling `ssim-cie94` by default on
ionic-framework test suite, and it proves to be overly strict for their
usecase.
The option defines a comparator to be used to compare images.
Possible values are `"pixelmatch"` and `"ssim-cie94"`.
Note: This reverts commit 8167f8bf548308ad8c6f1188508aadee84f26023.
This patch implements a new image comparison function, codenamed
"ssim-cie94". The goal of the new comparison function is to cancel out
browser non-determenistic rendering.
To use the new comparison function:
```ts
await expect(page).toHaveScreenshot({
comparator: 'ssim-cie94',
});
```
As of Nov 30, 2022, we identified the following sources of
non-determenistic rendering for Chromium:
- Anti-aliasing for certain shapes might be different due to the
way skia rasterizes certain shapes.
- Color blending might be different on `x86` and `aarch64`
architectures.
The new function employs a few heuristics to fight these
differences.
Consider two non-equal image pixels `(r1, g1, b1)` and `(r2, g2, b2)`:
1. If the [CIE94] metric is less then 1.0, then we consider these pixels
**EQUAL**. (The value `1.0` is the [just-noticeable difference] for
[CIE94].). Otherwise, proceed to next step.
1. If all the 8 neighbors of the first pixel match its color, or
if the 8 neighbors of the second pixel match its color, then these
pixels are **DIFFERENT**. (In case of anti-aliasing, some of the
direct neighbors have to be blended up or down.) Otherwise, proceed
to next step.
1. If SSIM in some locality around the different pixels is more than
0.99, then consider this pixels to be **EQUAL**. Otherwise, mark them
as **DIFFERENT**. (Local SSIM for anti-aliased pixels turns out to be
very close to 1.0).
[CIE94]: https://en.wikipedia.org/wiki/Color_difference#CIE94
[just-noticeable difference]:
https://en.wikipedia.org/wiki/Just-noticeable_difference
Resolves#14255.
PNGs should be preferred as they are deterministic, but increasing this
limit should be fine for JPEG users. (Looking through jpeg-js source code, the actual memory allocation is based on the size of the image—so unless a user is hitting this limit already—this should not impact the memory consumption of Playwright.
This patch aligns the strategies that are used to generate new
screnshot expectations and to compare screenshot expectations against
baseline.
With this patch, `toHaveScreenshot` will:
- when generating a new expectation: will wait for 2 consecutive
screenshots to match and accept the last one as expectation.
- when given an expectation:
* will compare first screenshot against expectation. If matches,
resolve successfully
* if first screenshot doesn't match, then wait for 2 consecutive
screenshots to match and then compare last screenshot with the
expectation.
An example of a new detailed call log:
```
1) a.spec.ts:3:1 › should work ===================================================================
Error: Screenshot comparison failed:
20000 pixels (ratio 0.03 of all image pixels) are different
Call log:
- expect.toHaveScreenshot with timeout 5000ms
- verifying given screenshot expectation
- fast-path: checking first screenshot to match expectation
- taking page screenshot
- disabled all CSS animations
- waiting for fonts to load...
- fonts in all frames are loaded
- fast-path failed: first screenshot did not match expectation - 20000 pixels (ratio 0.03 of all image pixels) are different
- waiting for 2 consecutive screenshots to match
- waiting 100ms before taking screenshot
- taking page screenshot
- disabled all CSS animations
- waiting for fonts to load...
- fonts in all frames are loaded
- 2 consecutive screenshots matched
- final screenshot did not match expectation - 20000 pixels (ratio 0.03 of all image pixels) are different
- 20000 pixels (ratio 0.03 of all image pixels) are different
Expected: /Users/andreylushnikov/tmp/test-results/a-should-work/should-work-1-expected.png
Received: /Users/andreylushnikov/tmp/test-results/a-should-work/should-work-1-actual.png
Diff: /Users/andreylushnikov/tmp/test-results/a-should-work/should-work-1-diff.png
3 | test('should work', async ({ page }) => {
4 | await page.goto('file:///Users/andreylushnikov/prog/playwright/tests/assets/rotate-z.html');
> 5 | await expect(page).toHaveScreenshot();
| ^
6 | });
7 |
```
