[osg-users] how to set the model view projection matrix for my own vertex shader

[Gianluca Natale]

Hi all.

First of all, sorry if mine is a silly question, I’m quite new to using shaders in OSG.

 

My scenario is this:

I have a vertex shader that gets as uniform in-variable the model view projection matrix, “MVP_matrix” is the name of that variable in my shader.

The shader is written in GL4.3, so I cannot rely upon the deprecated built-in variable gl_ModelViewProjection matrix.

Now, I have to attach such shader in a program that is set in a state set used to render my geometry (that state set is attached to the geode that contains my drawable, where the geometry is defined).

So, I would like that OSG automatically passes the model view projection matrix to my shader during rendering traversal.

I’ve seen in some OSG code that there is a predefined in-variable called “osg_ModelViewProjectionMatrix” that I think is filled by OSG during rendering traversal with the current model view projection matrix. Is that correct?

So, should I rely upon it in my shader, basically replacing my “MVP_matrix” with “osg_ModelViewProjectionMatrix”?

 

Further question: unfortunately the shader I have to use is shared among other applications in my company, and not all of them use OSG for rendering (some use pure OpenGL) L

So it’s likely that I cannot modify it (otherwise I should ask all developers to change the name of the in-variable they pass directly to the shader to “osg_ModelViewProjectionMatrix”).

Hence the question: if I’m forced to use “MVP_matrix”, is there a way I can tell OSG to set automatically the value of “osg_ModelViewProjectionMatrix” to “MVP_matrix” at run-time, i.e. during rendering traversal?

 

Thanks,

Gianluca

 

[Robert Osfield]

Hi Gianluca,

osg_ModelViewProjectionMatrix is the OSG's equivilant to gl_ModelViewProjectMatrix, and there is a mechanism in osg::State that can replace gl_ModelViewMatrixProjectMatrix usage in shaders with the osg_ equivalent at runtime.  There isn't however a general customizable support for setting and substituting your own uniforms in this role.

In your own application I'd suggest when you set up your osg::Shader with the shader source you replace the MVP_matrix usage with gl_ or osg_ equivalent.

Robert.

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[Gianluca Natale]

Oh yes, Robert,

that’s the most obvious and quickest solution, sorry for the silly question!

Once loaded my shader source code from the file, I’ll replace all the occurrences of “MVP_matrix” with “osg_ModelViewProjectionMatrix”, and OSG will update it for me during rendering traversal.

 

Thanks a lot! J

Gianluca

 

Da: osg-users [mailto:osg-user...@lists.openscenegraph.org] Per conto di Robert Osfield
Inviato: martedì 2 settembre 2014 13:56
A: OpenSceneGraph Users
Oggetto: Re: [osg-users] how to set the model view projection matrix for my own vertex shader