Bug 116991 – drawImage: clip source image when source rectangle outside of source image.

• Status: RESOLVED
• Resolution: FIXED
• Component: Canvas

[arno.]

Hi,
drawImage specification tells:
When the source rectangle is outside the source image, the source rectangle must be clipped to the source image and the destination rectangle must be clipped in the same proportion.[1]
Right now, when that happens, we draw nothing.
Firefox gets it right (at least for HTMLImageElement; for HTMLCanvasElement, there are some strange artifacts)

[1]: http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dom-context-2d-drawimage

[arno.]

Created attachment 203267 [details]
testcase: should display a quarter of circle

[arno.]

Created attachment 203279 [details]
patch proposal

This patches address the issue, and also create a new methode to factorise dimensions checking between the 3 drawImage main methods

[WebKit Commit Bot]

Attachment 203279 [details] did not pass style-queue:

Failed to run "['Tools/Scripts/check-webkit-style', '--diff-files', u'LayoutTests/ChangeLog', u'LayoutTests/fast/canvas/drawImage-source-rect-outside-image-expected.html', u'LayoutTests/fast/canvas/drawImage-source-rect-outside-image.html', u'Source/WebCore/ChangeLog', u'Source/WebCore/html/canvas/CanvasRenderingContext2D.cpp', u'Source/WebCore/html/canvas/CanvasRenderingContext2D.h']" exit_code: 1
Source/WebCore/html/canvas/CanvasRenderingContext2D.cpp:1274:  Place brace on its own line for function definitions.  [whitespace/braces] [4]
Total errors found: 1 in 6 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[arno.]

Created attachment 203301 [details]
updated patch: use normalized rect when drawImage video + style issues

[Brent Fulgham]

This continues to be a problem in Safari 16.

[Radar WebKit Bug Importer]

<rdar://problem/97222886>

[Brent Fulgham]

Pull request: https://github.com/Webkit/WebKit/pull/2640

[EWS]

Committed 252731@main (a31e58979ddb): <https://commits.webkit.org/252731@main>

Reviewed commits have been landed. Closing PR #2640 and removing active labels.

[Said Abou-Hallawa]

Altering the source rectangle is wrong. The fix of this bug was trying to scale the destination rectangle to match the clipped source rectangle.

For the record, I think the approach of fixing this bug was incorrect.