[whatwg] [canvas] imageRenderingQuality property

Philip Taylor excors+whatwg at gmail.com
Mon Jun 30 17:04:49 PDT 2008

On 01/07/2008, Ian Hickson <ian at hixie.ch> wrote:
> [...]
>  It seems better for the browser to simply detect when the graphics burden
>  being placed on the hardware by the page is too much to be done at high
>  quality given the current load on the CPU, and for the browser to
>  automatically drop down to a lower fidelity, higher speed rendering on the
>  fly when appropriate.

Sometimes the author will want to force best-quality rendering,
regardless of the performance impact. E.g. a photo manipulation
application might let you resize a segment of a photo, displaying a
live preview (where performance is more important than quality), and
then render the final resized image and store it in a canvas for
future processing. That final rendering needs to be the best possible
quality, so it's not acceptable for the browser to decide that it
should semi-randomly drop the quality because it detected the live
preview was CPU-intensive.

Similarly, a pseudo-3d FPS game might load textures at runtime and
perform some preprocessing (like resizing to be square, and rendering
lots of smaller copies to be used as mipmaps for distant walls so they
look prettier), and then draw that processed texture into the game
thousands of times a second. Since the preprocessing is only done
once, and its result is reused for the whole of the rest of the game,
it should be done at the highest possible quality, regardless of

So, adaptively reducing the quality and allowing no author control
seems like a bad idea.

Perhaps the imageRenderingQuality property could have values 'high'
and 'auto', where the default is 'high' (so that existing content
continues working the same as it always has, and to avoid surprising
authors by randomly switching the rendering quality when they have no
reason to expect such weird behaviour), and 'auto' means 'low (but
perhaps switch to high if the browser thinks it's going to be fast
enough)'. That would avoid the issue of authors setting quality='low'
and preventing high-speed users from getting the best quality output.

Philip Taylor
excors at gmail.com

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