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Re: 7-arg drawImage() call

From: Philip Taylor <pjt47@cam.ac.uk>
Date: Sat, 17 Jul 2010 11:51:30 +0100
Message-ID: <4C418B32.9000908@cam.ac.uk>
To: Jatinder Mann <jmann@microsoft.com>
CC: "'public-canvas-api@w3.org' (public-canvas-api@w3.org)" <public-canvas-api@w3.org>
Jatinder Mann wrote:
> The following text from Section 12 Images [1] seems to imply a
> 7-argument drawImage() call:
> "If not specified, the dw and dh arguments must default to the values
> of sw and sh, interpreted such that one CSS pixel in the image is
> treated as one unit in the canvas coordinate space."
> To not specify those two arguments would be to make a function call
> like so: drawImage(image, sx, sy, sw, dx, dy). In the latest version
> of the spec, such a drawImage function call is not specified and
> neither do any of the major browser vendors implement this function.

The normative definition of the overloads 
(http://dev.w3.org/html5/2dcontext/#canvasrenderingcontext2d) is:

   void drawImage(in HTML[...]Element image, in float dx, in float dy, 
in optional float dw, in float dh);

   void drawImage(in HTML[...]Element image, in float sx, in float sy, 
in float sw, in float sh, in float dx, in float dy, in float dw, in 
float dh);

The last two arguments in the first overload are optional, so you can 
call "drawImage(image, dx, dy)". That's the case where dw/dh are not 
specified and default to sw/sh, which that spec sentence is referring 
to. I don't see why it would be interpreted as referring to overloads 
that are never defined and can never be called. Can you suggest specific 
text that would make it clearer?

Philip Taylor
Received on Saturday, 17 July 2010 10:51:59 UTC

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