[whatwg] createImageData

Vladimir Vukicevic vladimir at pobox.com
Sat May 10 19:13:21 PDT 2008

On May 10, 2008, at 5:44 PM, Oliver Hunt wrote:
> On May 10, 2008, at 4:53 PM, Vladimir Vukicevic wrote:
>> Another approach would be to not try to solve this in canvas at  
>> all, and instead specify that by default, all canvas elements are  
>> 96dpi, and provide authors a way to explicitly override this --  
>> then using a combination of CSS Media Queries and other CSS, the  
>> exact dpi desired could be specified.  (You can sort of do this  
>> today, given that the canvas width/height attributes are in CSS  
>> pixels, and that if CSS dimensions are present a canvas is scaled  
>> like an image... so canvas { width: 100px; height: 100px; } ...  
>> <canvas width="200" height="200"/> would give a 192dpi canvas  
>> today, no?)
> Canvas was designed with the intent of allowing resolution  
> independent, removing that intent in the name of a feature that is  
> not used in the general case seems to be a fairly substantial step  
> back from that goal.  Unfortunately the "solution" of using a larger  
> canvas scaled to fit a smaller region isn't a real solution.  For  
> lower resolution displays it results in higher memory usage and  
> greater computational cost than is otherwise necessary, and for high  
> dpi displays it results either the same issues as the low dpi case  
> (if the canvas resolution is still too high) or it results in a  
> lower resolution display than the display is capable of.

Eh?  The resolution used should be whatever the appropriate resolution  
should be;  I'm certainly not suggesting that everyone unilaterally  
create canvases with 2x pixel resolution, I'm saying that the features  
exist to allow authors to (dynamically) create a canvas at whatever  
the appropriate resolution is relative to CSS resolution.  Canvas was  
designed to allow for programmatic 2D rendering for web content;  
resolution independence would certainly be nice, but it was never a  
goal of the canvas spec.  In fact, the spec explicitly states that the  
"canvas element represents a resolution-dependent bitmap canvas".

     - Vlad

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