[whatwg] Need clarification on DOM exceptions thrown by canvas 2D drawImage

Ian Hickson ian at hixie.ch
Mon Aug 8 13:58:03 PDT 2011

On Mon, 8 Aug 2011, Justin Novosad wrote:
> This inquiry is regarding this page of the specification: 
> http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html 
> In section Images, about drawImage(), it is stated that "If 
> one of the sw or sh arguments is zero, the implementation must raise an 
> INDEX_SIZE_ERR exception"  There are no other references to other 
> circumstances under which INDEX_SIZE_ERR should be thrown, and there is 
> no indication of what the correct behavior is when the source rectangle 
> is completely or partially outside the bounds of the source image.

A bit lower down in the same section, the spec says: "When the filtering 
algorithm requires a pixel value from outside the original image data, it 
must instead use the value from the nearest edge pixel. (That is, the 
filter uses 'clamp-to-edge' behavior.)"

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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