Bug 163820 - Font variations animations are jumpy
Summary: Font variations animations are jumpy
Status: NEW
Alias: None
Product: WebKit
Classification: Unclassified
Component: Text (show other bugs)
Version: WebKit Nightly Build
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Myles C. Maxfield
Depends on:
Blocks: 162815
  Show dependency treegraph
Reported: 2016-10-21 17:01 PDT by Myles C. Maxfield
Modified: 2017-02-22 16:41 PST (History)
5 users (show)

See Also:

Patch (4.79 KB, patch)
2016-10-21 17:30 PDT, Myles C. Maxfield
simon.fraser: review-
Details | Formatted Diff | Diff
Broken web page (7.12 MB, application/x-webarchive)
2017-02-22 16:41 PST, zalan
no flags Details

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Description Myles C. Maxfield 2016-10-21 17:01:56 PDT
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.
Comment 1 Myles C. Maxfield 2016-10-21 17:30:27 PDT
Created attachment 292439 [details]
Comment 2 Simon Fraser (smfr) 2016-10-21 17:46:56 PDT
Comment on attachment 292439 [details]

I don' think we should do this now, but we might want to try to figure something out in future. This patch will blow the glyph cache if a variation font is used as body text.
Comment 3 zalan 2017-02-22 16:41:06 PST
Created attachment 302464 [details]
Broken web page