[whatwg] createImageData

[Oliver Hunt]

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.

Moreover using a larger canvas than necessary will result in much  
higher memory usage for engines like WebKit which do support high DPI  
displays, and so will end up with a scaled high resolution canvas.

--Oliver