[Webkit-unassigned] [Bug 241402] New: Decoded image data is not reused by canvas causing long task blocking on the main thread
bugzilla-daemon at webkit.org
bugzilla-daemon at webkit.org
Tue Jun 7 22:04:13 PDT 2022
https://bugs.webkit.org/show_bug.cgi?id=241402
Bug ID: 241402
Summary: Decoded image data is not reused by canvas causing
long task blocking on the main thread
Product: WebKit
Version: WebKit Nightly Build
Hardware: Unspecified
OS: Unspecified
Status: NEW
Severity: Normal
Priority: P2
Component: Canvas
Assignee: webkit-unassigned at lists.webkit.org
Reporter: xidorn-webkit at upsuper.org
CC: dino at apple.com
Created attachment 460082
--> https://bugs.webkit.org/attachment.cgi?id=460082&action=review
testcase
STR:
1. download the attachment and serve it and open it
2. click the button in the page
Expected result:
The decoding takes sometime, but drawing is instant, and there is no long task detected on the main thread.
Actual result:
Both the decoding and the drawing takes roughly the same amount of time, and there is a long task indicates the main thread is blocked.
Seemingly that the drawing the image on canvas then `getImageData` forces a decoding of the image even if the image is already decoded through `img.decode()`. It makes it hard to avoid a long task on main thread when dealing with large images.
Blink has similar issue: https://bugs.chromium.org/p/chromium/issues/detail?id=1334448
On Gecko, I get the expected result.
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