[osg-users] Multipass rendering with shader

[Andrea Martini]

Hi,
i'm wondering if is it possible to apply different shaders (vertex and fragment) on the same osg::Node (not entire scene as RTT image) in this way : The result (ouput) of the first vertex/fragment shader must be used as input of the second vertex/fragment shader. In example, i have used a vertex and fragment to get refraction effect. But, unless i write the proper vertex/fragment code in this refraction shader, i loose lights setting coming from osg code. I would like to set lights using a shader (vertex/fragment) on the osg::Node already affected by refraction shader.
Is there any example that show how to get it?

Thank you!

Cheers,
Andrea

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[Sebastian Messerschmidt]

Hello Andrea,

It sounds like you have two distinct problems.
The first is to render to texture and to use the texture as input for
your second pass. This is easy, take a look at the osgPreRender example.
Basically you render fullscreen to a FrameBufferObject and use the bound
texture in a second pass as input to your fragment shader.

Your second problem is to bind different states to the same nodes. This
can be done in different ways.
First option is to clone you graph, bind your second program and render
set it to your second-pass camera.


Another option is to bind the shaders at camera level, which depending
on your rendering model is the easiest way.

If you need to render the first pass with different shaders at different
nodes, but only one shader for all nodes at your second pass, you can
also simply bind it to the root/camera of your second pass and set it to
override.

Since you're talking about refraction: If you need refractive objects
like glass which refract the scene, you will need to make a copy of the
first pass result framebuffer (without refractive objects) and bind it
as input to your second pass to get the background distorted correctly.
But beware, this won't work nicely with other transparent objects.

cheers
Sebastian