[Webkit-unassigned] [Bug 163820] New: Font variations animations are jumpy

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=163820

            Bug ID: 163820
           Summary: Font variations animations are jumpy
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Text
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mmaxfield at apple.com
                CC: mmaxfield at apple.com

When animating through a variable font's design space on a 1x screen, the glyphs look like they are jumping from pixel to pixel.

This is because of sub pixel quantization. In particular, when passing true to CGContextSetShouldSubpixelQuantizeFonts(), there are fewer places within a pixel that a glyph can lie, so cache hit rates are higher (and vice-versa). When performing a variable font animation, there are not enough places within a pixel that a glyph can lie, so the glyphs appear to jump from pixel to pixel.

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