[osg-users] Default vertex shader

Denis Nikolskiy nikolski at arsc.edu
Thu Jul 24 11:19:44 PDT 2008

Hello Jean-Sebastien,

I followed your advice. Everything works well. Thanks a lot for  
clarifying those things and for your help.


On Jul 23, 2008, at 4:58 AM, Jean-Sébastien Guay wrote:

> Hello Denis,
>> When I added vertex shader, the object was not shadowed properly  
>> (with the same exact fragment shader). I suspect I'm doing  
>> something wrong with the texture coordinates in a vertex shader. I  
>> looked in ShadowMap.cpp, it has only fragment shaders. Do you know  
>> where can I find default vertex shader?
> When you start using a shader for one part of the pipeline (vertex  
> or fragment) you need to do everything that that part of the  
> pipeline used to do (and which is needed by your rendering). In the  
> case of shadows, you'll notice that the code in ShadowMap.cpp adds  
> an osg::TexGen that calculates some texture coordinates for texture  
> unit 1. But that's the fixed pipeline, so you will need to  
> calculate texture coordinates for unit 1 as glTexGen would in your  
> vertex shader now that it has replaced the fixed-function vertex  
> processing.
> Something like this should work, though you should probably have  
> finer control over when these are calculated or not:
>     gl_TexCoord[1].s = dot( ecPosition, gl_EyePlaneS[1] );
>     gl_TexCoord[1].t = dot( ecPosition, gl_EyePlaneT[1] );
>     gl_TexCoord[1].p = dot( ecPosition, gl_EyePlaneR[1] );
>     gl_TexCoord[1].q = dot( ecPosition, gl_EyePlaneQ[1] );
> Note that ecPosition is:
>     vec4 ecPosition = gl_ModelViewMatrix * gl_Vertex;
> I also assume you're transforming your texture coordinates for  
> texture unit 0 properly:
>     gl_TexCoord[0] = gl_TextureMatrix[0] * gl_MultiTexCoord0;
> Just assigning gl_MultiTexCoord0 to gl_TexCoord[0] will work until  
> you try to use a texture matrix (osg::TexMat)...
> I highly recommend you get/read the Orange Book, as this is all  
> given there. You can also download the ShaderGen program from  
> 3DLabs (now hosted on http://mew.cx/glsl since 3DLabs removed it  
> from their site) which can generate shaders that emulate the fixed  
> pipeline. Note that for speed, you should probably only use the  
> features you need in your shaders, so I am not recommending that  
> you generate a shader that does *all* of what the fixed pipeline  
> would do... Just use what ShaderGen produces as a guide.
> Hope this helps,
> J-S
> -- 
> ______________________________________________________
> Jean-Sebastien Guay    jean-sebastien.guay at cm-labs.com
>                                http://www.cm-labs.com/
>                         http://whitestar02.webhop.org/
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