[osg-users] Shaders with multiple views, possible?

[Julien Valentin]

Heu 
Why don't you use different uniform for your differents cameras?


arennuit wrote:
> Dear OSG forum,
> 
> I am having trouble using shaders in the context of multiple views (either several Viewer objects or a CompositeViewer). When using shaders (either vertex or fragment), you most often need to let the shaders know about the camera configuration. In the case where a single view (i.e. single camera) is used, this can be done via a ModelViewProjectionMatrix uniform and setting up a callback camera callback such that when the camera is updated, the shader is informed about the update:
> 
> 
> Code:
> 
> struct ModelViewProjectionMatrixCallback: public osg::Uniform::Callback {
> 	ModelViewProjectionMatrixCallback(osg::Camera* camera) :
> 			_camera(camera) {
> 	}
> 
> 	virtual void operator()(osg::Uniform* uniform, osg::NodeVisitor* nv) {
> 		osg::Matrixd viewMatrix = _camera->getViewMatrix();
> 		osg::Matrixd modelMatrix = osg::computeLocalToWorld(nv->getNodePath());
> 		osg::Matrixd modelViewProjectionMatrix = modelMatrix * viewMatrix * _camera->getProjectionMatrix();
> 		uniform->set(modelViewProjectionMatrix);
> 	}
> 
> 	osg::Camera* _camera;
> };
> 
> 
> osg::Uniform* modelViewProjectionMatrix = new osg::Uniform(osg::Uniform::FLOAT_MAT4, "ModelViewProjectionMatrix");
> modelViewProjectionMatrix->setUpdateCallback(new ModelViewProjectionMatrixCallback(camera));
> 
> 
> 
> 
> But in the case where multiple views are used, there are multiple cameras and if we install callbacks on all cameras, then the shader may be informed about camera 2 being updated but being rendering the view of camera 0. And in this case view 0 will be drawn with the configuration of camera 2, no?
> 
> I guess I am wrong somewhere? Or else what should I change in my code to get shaders in the context of multiple views?
> 
> Thank you!
> 
> Cheers,
> Antoine


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