Bug 163820

Summary: Font variations animations are jumpy
Product: WebKit Reporter: Myles C. Maxfield <mmaxfield>
Component: TextAssignee: Myles C. Maxfield <mmaxfield>
Status: NEW    
Severity: Normal CC: dino, jonlee, mmaxfield, simon.fraser, thorton
Priority: P2    
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   
Bug Depends on:    
Bug Blocks: 162815    
Attachments:
Description Flags
Patch
simon.fraser: review-
Broken web page none

Myles C. Maxfield
Reported 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.
Attachments
Patch (4.79 KB, patch)
2016-10-21 17:30 PDT, Myles C. Maxfield 		simon.fraser: review-
DetailsFormatted DiffDiff
Broken web page (7.12 MB, application/x-webarchive)
2017-02-22 16:41 PST, alan 		no flags
Details
View All Add attachment proposed patch, testcase, etc.
Myles C. Maxfield
Comment 1 2016-10-21 17:30:27 PDT
Created attachment 292439 [details] Patch
Simon Fraser (smfr)
Comment 2 2016-10-21 17:46:56 PDT
Comment on attachment 292439 [details] Patch 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.
alan
Comment 3 2017-02-22 16:41:06 PST
Created attachment 302464 [details] Broken web page
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