Bug 181641

Summary: Drawing semitransparent gradients with canvas and globalAlpha messes colors up
Product: WebKit Reporter: Cameron Little <cameron>
Component: CanvasAssignee: Nobody <webkit-unassigned>
Status: RESOLVED INVALID    
Severity: Normal CC: dino, simon.fraser, thorton
Priority: P2 Keywords: InRadar
Version: Safari Technology Preview   
Hardware: Mac   
OS: macOS 10.13   
Attachments:
Description Flags
Output from reproduction none

Cameron Little
Reported 2018-01-14 16:04:27 PST
Created attachment 331315 [details] Output from reproduction Canvas behaves differently when using globalAlpha vs alpha in an rgba color within a gradient. Colors look much muddier. Here's a reproduction: https://codepen.io/apexskier/pen/RxBgKq?editors=0010 This works when filling with a single color (not a gradient).
Attachments
Output from reproduction (107.15 KB, image/png)
2018-01-14 16:04 PST, Cameron Little 		no flags
Details
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Simon Fraser (smfr)
Comment 1 2018-01-16 11:24:23 PST
Seems to be a bug in the underlying framework we use for GPU-accelerated canvas drawing.
Simon Fraser (smfr)
Comment 2 2018-01-16 11:28:22 PST
rdar://problem/36551228
Alexey Proskuryakov
Comment 3 2018-01-20 17:33:40 PST
As such, marking INVALID, the issue will continue to be tracked by Apple internally. Thank you for the report!
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