[webkit-dev] WebGL performance

[Oliver Hunt]

On Oct 20, 2009, at 5:58 AM, Boris Stock wrote:

> I have an question regarding the WebGL implementation. It already  
> seems to be very fast. Of course a lot of stuff is important like in  
> "native" GL programs (rendering triangle stripes vs. X and stuff).  
> But how far do you think will a future stable release of WebGL match  
> a "native" GL implementation in performance? Is JavaScript speed a  
> big show stopper there? or because the GL surface is not fullscreen  
> and can be overlayed with other layers (which is also a big  
> peformance impact on any system which overlays something over the  
> opengl surface / view).

At the moment there are not any significant webgl based apps (due to  
the current state of the spec) so we don't yet know what issues will  
be performance problems.  On the topic of overlay performance, there  
is the requirement that a canvas element (WebGL or simple 2D) must  
composite correctly, which effectively requires a call to glReadPixels  
if the renderer is not able to composite on a hardware directly.

There are other costs that currently don't show up as they're not  
implemented, most notably shader validation -- basically the UA is  
required to parse shaders itself and validate against a reduced subset  
of the GL|ES 2.0 version of GLSL (which is a subset of desktop GLSL).

--Oliver

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