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
This patch:
- updates documentation to lead users from `TestConfig.snapshotDir` and
`testInfo.snapshotSuffix` to `TestConfig.snapshotPathTemplate` as a
better and more flexible alternative.
- drops `{snapshotSuffix}` from documentation
- stops using `snapshotSuffix = ''` in our own tests and switches us
to the `snapshotPathTemplate`.
- adds `{testName}` token.
This configuration option allows to set a string with template
values for precise control over snapshot path location.
An example of `snapshotPathTemplate` usage:
```ts
// playwright.config.ts
// Notice the `testDir` configuration!
export default {
testDir: './tests',
snapshotPathTemplate: './__screenshots__/{platform}/{projectName}/{testFilePath}/{arg}{ext}',
}
```
Currently supported "magic tokens" inside the `snapshotPathTemplate`
are:
- `{testDir}` - project's `testDir`
- `{snapshotDir}` - project's `snapshotDir`
- `{platform}` - `process.platform`
- `{projectName}` - Project's sanitized name
- `{testFileDir}` - Directories in relative path from `testDir` to test
file path (e.g. `page/` in the example below)
- `{testFileName}` - Test file name (with extension) (e.g.
`page-click.spec.ts` in the example below)
- `{testFilePath}` - Relative path from `testDir` to test file path
(e.g. `page/page-click.spec.ts` in the example below)
- `{ext}` - snapshot extension (with dots)
- `{arg}` - joined snapshot name parts, without extension (e.g.
`foo/bar/baz` in the example below)
- `{snapshotSuffix}` - `testInfo.snapshotSuffix` value.
Consider the following file structure:
```
playwright.config.ts
tests/
└── page/
└── page-click.spec.ts
```
The following `page-click.spec.ts`:
```ts
// page-click.spec.ts
import { test, expect } from '@playwright/test';
test('should work', async ({ page }) => {
await expect(page).toHaveScreenshot(['foo', 'bar', 'baz.png']);
});
```
Fixes#7792
Per discussion in #12950, adding sanitized name to the output filename
prefix. This can make debugging easier, and the filename structure more
human friendly.
