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Re: [Public WebGL] Render to texture



On Mon, Aug 30, 2010 at 1:25 PM,  <steve@sjbaker.org> wrote:
>> On Mon, Aug 30, 2010 at 12:20 PM,  <steve@sjbaker.org> wrote:
>>> So is going via the DOM/canvas mechanism likely to hurt performance with
>>> present implementations?  Would the image be copied from place to place?
>>> (I confess my knowledge of what's going on here is a little vague -
>>> please
>>> educate me!)  Is there no way to render directly into a texture without
>>> involving a canvas?
>>
>> Yes, there will currently be a significant performance penalty
>> involved with rendering WebGL to one canvas and then uploading it as a
>> texture to another one (or even within the same context -- although
>> you can get the same effect with copyTexSubImage2D). This is true at
>> least in the WebKit WebGL implementation.
>
> I suppose there is at least some hope that copyTexSubImage2D would happen
> entirely within the GPU...that might not be too terrible.

It does.

>> The recommended way to perform render-to-texture of the color buffers
>> in WebGL is to allocate an FBO and attach a texture as the color
>> attachment. This functionality is supposed to be guaranteed on any
>> platform claiming WebGL support. Note though the OpenGL ES 2.0 NPOT
>> restrictions; see
>> http://khronos.org/webgl/wiki/WebGL_and_OpenGL_Differences .
>>
>> -Ken
>
> Is there an example someplace that uses the 'recommended' FBO approach?

The only one that comes to mind is the render target implementation in
O3D/WebGL. See http://code.google.com/p/o3d/ and
http://code.google.com/p/o3d/downloads/list . I'm sure others on this
list will have additional recommendations.

-Ken

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