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[Bug 19820] New: Description of transformation in drawimage is confusing

From: <bugzilla@jessica.w3.org>
Date: Thu, 01 Nov 2012 15:45:39 +0000
To: public-html@w3.org
Message-ID: <bug-19820-2495@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=19820

          Priority: P2
            Bug ID: 19820
                CC: mike@w3.org, public-html-wg-issue-tracking@w3.org,
                    public-html@w3.org
          Assignee: jaymunro@microsoft.com
           Summary: Description of transformation in drawimage is
                    confusing
        QA Contact: public-html-bugzilla@w3.org
          Severity: normal
    Classification: Unclassified
                OS: All
          Reporter: cabanier@adobe.com
          Hardware: PC
            Status: NEW
           Version: unspecified
         Component: HTML Canvas 2D Context
           Product: HTML WG

See: http://www.w3.org/TR/2dcontext/#drawing-images-to-the-canvas

The text for drawImage currently states:
When drawImage() is invoked, the region of the image specified by the source
rectangle must be painted on the region of the canvas specified by the
destination rectangle, after applying the current transformation matrix to the
points of the destination rectangle.

This is a bit confusing since you don't really apply the transform to the
points. Basically, you map the source rect to the destination rect and then
transform the destination rectangle.
I believe the spec should also call out that there should be no loss of
precision when doing this (i.e. if the destination has half the pixels but
scaled by 2, the original pixel should be preserve)

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Received on Thursday, 1 November 2012 15:45:40 GMT

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