[Public WebGL] questions about vertexAttribPointer / getVertexAttrib offsets

Benoit Jacob [email protected]
Mon Apr 23 12:56:10 PDT 2012


----- Original Message -----

> On Mon, Apr 23, 2012 at 12:06 PM, Boris Zbarsky < [email protected] >
> wrote:

> > On 4/23/12 2:43 PM, Gregg Tavares (勤) wrote:
> 

> > > There's at least one negative offset test in
> > 
> 
> > > https://cvs.khronos.org/svn/ repos/registry/trunk/public/
> > > webgl/sdk/tests/conformance/ more/functions/
> > > vertexAttribPointerBadArgs. html
> > 
> 

> > Doesn't that call fail per current spec because the offset (-1) is
> > not a multiple of sizeof(float), independently of what negative
> > offset handling looks like? My Gecko build with the negative offset
> > check in vertexAttribPointer removed passes this test, precisely
> > for
> > that reason:
> 

> > VertexAttribPointer: byteOffset doesn't satisfy the alignment
> > requirement of given type @ https://cvs.khronos.org/svn/
> > repos/registry/trunk/public/ webgl/sdk/tests/conformance/
> > more/util.js:965
> 

> > -Boris
> 

> To be clear

> 1) AFAICT OpenGL does not allow negative offsets

> 2) WebGL should not allow them either.

> So,

> a) we should update the WebGL spec to make it clear negative offsets
> generate INVALID_VALUE

> and

> b) we should update the conformance tests to test that case.

> Agree?
I agree, except for 1): I don't see where the OpenGL spec forbids negative offsets. I agree that there doesn't seem to exist a valid use case for them. I would support forbidding negative offsets in WebGL for now, and having a conversation on that topic with the OpenGL WG. 

Benoit 
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