[whatwg] Canvas in Workers

[Mark Callow]

On 2013/01/04 9:46, Gregg Tavares wrote:
> On Tue, Dec 11, 2012 at 9:04 AM, Ian Hickson <ian at hixie.ch> wrote:
>
>> On Tue, 11 Dec 2012, Gregg Tavares (社ç~T¨) wrote:
>>> In WebGL land we have creation attributes on the drawingbuffer made for a
>>> canvas. Example
>>>
>>>     gl = canvas.getContext("webgl", { preserveDrawingBuffer: false });
>>>
>>> We're working out the details on how to set those options for the case
>>> where we have 1 context and multiple canvases.
>>>
>>> The particular option above would apparently be a huge perf win for
>>> canvas 2d for mobile. Which suggests that whatever API is decided on it
>>> would be nice if it worked for both APIs the same.
>> What does it do?
>>
> Effectively it makes the canvas double buffered.

The reason for this attribute and defaulting it to false, is so that
tiled renderers can avoid copying the area of the previously-rendered
drawing buffer corresponding to the current tile, into tile memory prior
to rendering. Avoiding this copy is a big performance and power win for
tiled renderers. As far as I am aware every mobile GPU, with the
exception of NVIDIA's Tegra, is a tiled renderer so supporting them is
very important.

I would expect these wins to be equally important when doing animation
in Canvas2D as I would double buffering to to avoid flicker.

Regards

    -Mark

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