[osg-users] Vertex texture fetch in r600+ ATI cards

Marko Srebre marko_srebre at t-2.net
Fri Jul 18 10:43:17 PDT 2008

This sure was a tough one. It's a weird hack.

To make osgshaderterrain example work on Radeon cards with VTF support, 
you have to add something like this to the vertex shader code:

uniform sampler2D baseTexture;


vec4 dummy_lookup = texture2D(baseTexture, texcoord);

Also I get some queer behaviour when using two textures in fragment 
program... ati opengl support seems quite buggy and unpredictable.

Marko wrote:
> This is my first post on the lists; hello to everybody and thanks for 
> all the precious info I gathered here in one year of working with 
> openscenegraph.
> I have a RadeonHD 3850 card working fine with fglrx driver (8.6) in Linux.
> I have problems running osgshaderterrain example. I get repetitions of 
> this error:
> Warning: detected OpenGL error 'invalid value' after RenderBin::draw(,)
> The cause of warning is texture2d() lookup in vertex shader, if I remove 
> this, the error disappears.
> ATI/AMD claims vertex texture fetch is supported by all ATI hardware 
> since r600 (Radeon HD2xxx), so I though at first it may be a driver 
> issue. Googling around I found some posts saying the drivers 8.5 should 
> support VTF in GLSL, but that may have been about Windows drivers.
> I used the check in osgshaderterrain and queryed 
> GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS. It returns 16. As I understand this 
> means the vertex fetch should be supported. So what could be the 
> problem, the texture format? Besides GL_LUMINANCE_FLOAT32_ATI, I tried 
> GL_LUMINANCE32F_ARB and GL_RGBA32F_ARB, with no better results.
> Is this a driver issue/bug? Has anyone managed to run VTF on ATI cards? 
> What about Windows users, it would be helpful to know if 
> osgshaderterrain runs there, since the drivers (8.5+) supposedly support 
> it.
> Any hints on where to look for information are most welcome. Thanks.
> Marko
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