[osg-users] osg_Vertex with GL compatibility profile

[Robert Osfield]

On 17 September 2016 at 18:39, Sebastian Messerschmidt
<sebastian.messerschmidt at gmx.de> wrote:
> Hi Ravi,
>
> Thanks Robert!
>
> So do you know why using osg_Vertex works *without* using
> setUseVertexAttributeAliasing() on so many machines? I am compiling OSG with
> GL2 (no GL3 flags) on all machines. Is it just "undocumented behavior"?
>
> That is probably simply by chance, since the vertex attribute is usually the
> first one in the stream. The compiler will map the first attribute there. So
> basically this works most of the time.

This sounds plausible.

> Next question: if I use setUseVertexAttributeAliasing, then many of my
> textured polygons (e.g. Sphere) have what appears to be a flat color on
> them. The actual color used seems to be related to one point on the texture.
>
> I see similar behavior if I run the "osgvertexattributes cow.osg" example
> (see attachment). Is Vertex Attribute Aliasing something that's only
> intended for GL3?
>
> The cow model might not have texture coordinates but generated texture
> coordinates. I can't test the example right now, but maybe this is the
> reason. Usually when you go with vertex attribute aliasing you need to use
> an appropriate shader for the data.

The cow.osgt uses tex gen to generate the texture coordinates.

Robert.