[Webkit-unassigned] [Bug 201326] [Cairo] Scaled tile painting is slow

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=201326

--- Comment #8 from Fujii Hironori <Hironori.Fujii at sony.com> ---
Created attachment 386403

  --> https://bugs.webkit.org/attachment.cgi?id=386403&action=review

test case scaling a tile image by 0.75x

There is a comment in _cairo_pattern_analyze_filter:
https://github.com/freedesktop/cairo/blob/f93fc72c0c3e158982740015304389192ce8a567/src/cairo-pattern.c#L3438

>  /* Use BILINEAR for any scale greater than .75 instead
>   * of GOOD. For scales of 1 and larger this is identical,
>   * for the smaller sizes it was judged that the artifacts
>   * were not worse than the artifacts from a box filer.
>   * BILINEAR can also be used if the scale is exactly .5
>   * and the translation in that direction is an integer.
>   */

Cairo uses BILINEAR filter if the filter is CAIRO_FILTER_GOOD and the scale factor is greater than 0.75.

If the scale factor is less than or equal to 0.75, the issue happens.
The attached test case is scaling 16x16 image to 12x12, which is 0.75 scale factor.
The issue happens if it is opened with 1.0 device scale factor display.

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