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Update web-platform-tests to revision 8a14626934f5748a4ea6210847a02c0d8bbc8560

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65
tests/wpt/web-platform-tests/docs/_writing-tests/reftests.md
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@ -112,10 +112,67 @@ only guaranteed to be after those events.
## Fuzzy Matching
In some situations a test may have subtle differences in rendering
compared to the reference due to, e.g., anti-aliasing. This may cause
the test to pass on some platforms but fail on others. In this case
some affordance for subtle discrepancies is desirable. However no
mechanism to allow this has yet been standardized.
compared to the reference due to, e.g., anti-aliasing. To allow for
these small differences, we allow tests to specify a fuzziness
characterised by two parameters, both of which must be specified:
* A maximum difference in the per-channel color value for any pixel.
* A number of total pixels that may be different.
The maximum difference in the per pixel color value is formally
defined as follows: let <code>T<sub>x,y,c</sub></code> be the value of
colour channel `c` at pixel coordinates `x`, `y` in the test image and
<code>R<sub>x,y,c</sub></code> be the corresponding value in the
reference image, and let <code>width</code> and <code>height</code> be
the dimensions of the image in pixels. Then <code>maxDifference =
max<sub>x=[0,width) y=[0,height), c={r,g,b}</sub>(|T<sub>x,y,c</sub> -
R<sub>x,y,c</sub>|)</code>.
To specify the fuzziness in the test file one may add a `<meta
name=fuzzy>` element (or, in the case of more complex tests, to any
page containing the `<link rel=[mis]match>` elements). In the simplest
case this has a `content` attribute containing the parameters above,
separated by a colon e.g.
```
<meta name=fuzzy content="maxDifference=15;totalPixels=300">
```
would allow for a difference of exactly 15 / 255 on any color channel
and 300 exactly pixels total difference. The argument names are optional
and may be elided; the above is the same as:
```
<meta name=fuzzy content="15;300">
```
The values may also be given as ranges e.g.
```
<meta name=fuzzy content="maxDifference=10-15;totalPixels=200-300">
```
or
```
<meta name=fuzzy content="10-15;200-300">
```
In this case the maximum pixel difference must be in the range
`10-15` and the total number of different pixels must be in the range
`200-300`.
In cases where a single test has multiple possible refs and the
fuzziness is not the same for all refs, a ref may be specified by
prefixing the `content` value with the relative url for the ref e.g.
```
<meta name=fuzzy content="option1-ref.html:10-15;200-300">
```
One meta element is required per reference requiring a unique
fuzziness value, but any unprefixed value will automatically be
applied to any ref that doesn't have a more specific value.
## Limitations