Bug 214259

Summary: REGRESSION(r264280) [GTK][WPE] fast/gradients/conic-gradient-alpha.html is failing
Product: WebKit Reporter: Lauro Moura <lmoura>
Component: WebKitGTKAssignee: Nobody <webkit-unassigned>
Status: RESOLVED FIXED    
Severity: Normal CC: bugs-noreply, cgarcia, clopez, darin
Priority: P2    
Version: WebKit Nightly Build   
Hardware: Unspecified   
OS: Unspecified   
See Also: https://bugs.webkit.org/show_bug.cgi?id=214221
Attachments:
Description Flags
Patch darin: review+

Description Lauro Moura 2020-07-13 09:56:07 PDT 
Instead of the green conics, only grayscale ones.

History: https://results.webkit.org/?suite=layout-tests&test=fast%2Fgradients%2Fconic-gradient-alpha.html
Comment 1 Darin Adler 2020-07-13 10:32:26 PDT 
Oops, looks like I broke this. Happy to help fix it.
Comment 2 Darin Adler 2020-07-13 13:24:01 PDT 
Any indication what’s going wrong yet?
Comment 3 Carlos Alberto Lopez Perez 2020-07-13 18:00:22 PDT 
It seems the generated gradient is now black&white: https://build.webkit.org/results/GTK%20Linux%2064-bit%20Release%20(Tests)/r264280%20(14625)/fast/gradients/conic-gradient-alpha-diffs.html
Comment 4 Darin Adler 2020-07-13 18:10:29 PDT 
Maybe a bug in the blend function?
Comment 5 Carlos Garcia Campos 2020-07-15 06:27:41 PDT 
There are two problems:

1. Now the blend is done using premultiplied alpha, since the first color stop is #00FF0000, the premultiplied is just 0, so we always end up with black color. So, just changing to use blendWithoutPremultiply() would fix the bug but...

2. There's a bug in blendWithoutPremultiply(), from is used in both fromSRGB and toSRGB.

Fixing 1 and 2 I get the right output, but the test doesn't pass yet, there's a one pixel difference for some reason.
Comment 6 Carlos Garcia Campos 2020-07-15 06:31:13 PDT 
Created attachment 404338 [details]
Patch
Comment 7 Darin Adler 2020-07-15 09:48:17 PDT 
Comment on attachment 404338 [details]
Patch

Nice! Thanks, this seems like a great fix.
Comment 8 Carlos Garcia Campos 2020-07-16 01:22:06 PDT 
Committed r264449: <https://trac.webkit.org/changeset/264449>