The option defines a comparator to be used to compare images.
Possible values are `"pixelmatch"` and `"ssim-cie94"`.
Note: This reverts commit 8167f8bf548308ad8c6f1188508aadee84f26023.
This is a new web-first assertion that should be used like this:
```ts
test('should work', async ({ page }) => {
const locator = page.locator('body');
// New web-first assertion.
await expect(locator).toIntersectViewport();
// The same functionality.
await expect.poll(() => locator.viewportRatio()).toBeGreaterThan(0);
});
```
Fixes#8740
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
The following was before:
```txt
typing.Union[
typing.List[typing.Union[typing.Pattern[str], str]],
typing.Pattern[str],
str,
]
```
but it should be:
```txt
typing.Union[
typing.List[typing.Pattern[str]],
typing.List[str],
typing.List[typing.Union[typing.Pattern[str], str]],
typing.Pattern[str],
str,
]
```
Otherwise mypy yells at us.
See https://github.com/microsoft/playwright-python/issues/1524
This patch changes `expect(locator).toHaveAttribute()` so that the
`value` argument can be omitted. When done so, the method will
assert attribute existance.
Fixes#16517
