[whatwg] [canvas] imageRenderingQuality property

Oliver Hunt oliver at apple.com
Mon Jun 2 15:52:39 PDT 2008

On Jun 2, 2008, at 3:19 PM, Robert O'Callahan wrote:

> On Tue, Jun 3, 2008 at 9:39 AM, Oliver Hunt <oliver at apple.com> wrote:
> That's exactly what i would be afraid of people doing.  If I have a  
> fast system why should i have to experience low quality rendering?   
> It should be the job of the platform to determine what level of  
> performance or quality can be achieved on a given device.
> Right, it is. The user-agent is free to map all property values to  
> "maximum quality".
> Typically such a property would be considered a "hint", and as such  
> would likely be ignored.
> Ignored by who?

Given a few years all UA's as the majority of content saying "low  
quality" will be old, and therefore targeting slower UAs and platforms  
(given moore's law, and the fact that all UAs are currently getting  
faster this seems a reasonable assertion) so respecting it would mean  
the majority of sites using low quality mode would not need to.

> Neither of these apply if the property were just a hint, but now you  
> have to think about what happens to content that uses this property  
> in 18 months time.  You've told the UA to use a low quality  
> rendering when it may no longer be necessary, so now the UA has a  
> choice it either always obeys the property meaning lower quality  
> than is necessary so that new content performs well, or it ignores  
> the property in which case new content performs badly.
> If the quality knob is no longer necessary, why would new content  
> perform badly?
The issue is not that certain operations are slower than others, the  
issue is that anything that requires the developer to choose between  
performance/quality is going to become obsolete as the performance  
trade offs are constantly moving and are not the same from UA to UA,  
from platform to platform.  I think the issue of performance is a  
complex one that will not benefit in the long term from a simple on  
off switch.  Conceivably we could introduce new rendering primitives,  
such as CanvasSprite, CanvasLayer, or some such which would, i  
suspect, provide a similar benefit, but be more resilient in the face  
of changing performance characteristics.

> Rob


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