Bug 93344

Summary: CanvasRenderingContext2D::createPattern() should return null, if non-decodable image argument
Product: WebKit Reporter: Jussi Kukkonen (jku) <jussi.kukkonen>
Component: CanvasAssignee: Nobody <webkit-unassigned>
Status: UNCONFIRMED ---    
Severity: Normal    
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   

Description Jussi Kukkonen (jku) 2012-08-07 01:07:51 PDT
Spec says: "If the image argument is an HTMLImageElement object that is not fully decodable ... then the implementation must return null." This does not currently happen so these tests fail:
  canvas/philip/tests/2d.pattern.image.broken.html = TEXT
  canvas/philip/tests/2d.pattern.image.incomplete.empty.html = TEXT
  canvas/philip/tests/2d.pattern.image.incomplete.omitted.html = TEXT

HTMLImageElement does not seem to have "decodability" as a property and things are slightly complicated by the img.complete property being slightly illogical for this: currently images with empty, missing or non-existing source are "complete" (and IIRC this is according to current spec). So possibly these cases would have to be tested in CanvasRenderingContext2D. I'll take a closer look, advice is welcome also.
Comment 1 Jussi Kukkonen (jku) 2012-08-07 01:24:11 PDT
to improve searchability: above comment relates to CanvasRenderingContext2D::createPattern()
Comment 2 Jussi Kukkonen (jku) 2012-08-08 06:12:55 PDT
After some testing:

works after checking image->src().isValid()) before creating pattern

needs knowledge of whether image really is decodable

the image url used in createPattern() ends up as the _page_ url because HTMLIMageElement does document().completeURL(). This would still work with knowledge of whether image really is decodable