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Re: [Public WebGL] readPixles() can't access float values (OES_texture_float interaction)




On Sep 19, 2011, at 11:36 AM, Kenneth Russell wrote:

> 
> On Mon, Sep 19, 2011 at 11:14 AM, Chris Marrin <cmarrin@apple.com> wrote:
>> 
>> On Sep 16, 2011, at 11:14 AM, Kenneth Russell wrote:
>> 
>>> 
>>> Shouldn't the existing need to check the framebuffer's status be
>>> sufficient? Applications that don't check for FBO completeness are by
>>> definition incorrectly written. These applications already have to
>>> request the floating-point texture extension from WebGL.
>> 
>> Are you saying an author should discover whether or not it's possible to create a FP FBO by trying and if the FBO is incomplete after the attempt, that's an indication that it's not supported? I don't think that has precedence. Seems like it's much better to use the extension mechanism. If the attempt to enable the extension fails, then it's not a feature that can be used.
> 
> There is certainly precedence for this behavior; it's how FBOs work in
> the OpenGL API. In OpenGL ES, only one combination of renderbuffer
> attachments' formats is required to be supported, and what combination
> that is is not defined (ES20 spec 2.0.25, Section 4.4.5, "Framebuffer
> Completeness", p. 119). Applications are supposed to check FBO
> completeness before rendering and try other combinations of
> attachments if their preferred configuration isn't supported.

I meant that there's no precedence in WebGL. Remember our extension mechanism differs from that of OpenGL. In WebGL you need to enable an extension to use it's feature(s). We should stick with that. If there's a feature not supported by GLES, we should require an extension to enable it.

> 
> I'm not in favor of adding a WebGL-specific extension that has to be
> separately enabled in order to attach FP textures to an FBO. If there
> were an ES20 extension defining FP framebuffer support, that would be
> a different question. Since there doesn't seem to be support in the ES
> working group to define such an extension, and since there's at least
> one piece of ES20 compliant hardware that exposes such support under
> the umbrella of OES_texture_half_float, I think we should leave render
> to FP texture support as an optional feature under WebGL's FP texture
> extensions.

The ability to render to a FP framebuffer (however you want to characterize that) is not supported by standard GLES. If we want to allow for it on platforms that support it, we should have an extension and only allow it when that extension is enabled. 

-----
~Chris
cmarrin@apple.com





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