[Bug 10799] drawImage/pattern filters underspecified

http://www.w3.org/Bugs/Public/show_bug.cgi?id=10799

--- Comment #14 from Vladimir Vukicevic (Mozilla) <vladimir@pobox.com> 2010-12-07 21:16:59 UTC ---
(In reply to comment #11)
> For createPattern, add the text:
> 
> """
> If the original image data is a bitmap image, the value painted at a point in
> the area of the repetitions is computed by filtering the original image data.
> The user agent may use any filtering algorithm (for example bilinear
> interpolation or nearest-neighbor). When the filtering algorithm requires a
> pixel value from outside the original image data, it must instead use the value
> from wrapping the pixel's coordinates to the original image's dimensions. (That
> is, the filter uses 'repeat' behavior, regardless of the value of
> <var>repetition</var>.)

Hm, isn't this inconsistent?  For example, if the pattern uses no-repeat, and
is used to fill a rectangle larger than the pattern image size, this seems to
say that the no-repeat setting is ignored.  That seems odd and unexpected.

The clamp-to-edge behavior is fine for drawImage, but for patterns, I think the
only thing that mathematically makes sense is for the area outside of the
source pixels to be treated as transparent black for no-repeat.

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Received on Tuesday, 7 December 2010 21:17:00 UTC