[osg-users] Clip planes and instanced rendering

[Wojciech Lewandowski]

Hi Alberto,

You may need to add support for clip planes via gl_ClipVertex or
gl_ClipDistance to your shaders (which one depends on GLSL version used
-see
https://stackoverflow.com/questions/19125628/how-does-gl-clipvertex-work-relative-to-gl-clipdistance).
My experience with these vars was not always positive, though. I remember
times when I was unable to use them and once had to do my own cliping in
vertex shader (=major PITA). But maybe these days newer drivers or OSG
version make it easier.

Cheers,
WL

wt., 9 kwi 2019 o 12:41 Alberto Luaces <aluaces at udc.es> napisał(a):

> Hi,
>
> I want to set a clipping plane for my scene, but it is not working for
> instanced geometries.  I have not found any resource telling that
> clipping planes are ignored by GLSL.
>
> Simple test: if I make the following modifications to osgforest,
>
> diff --git a/examples/osgforest/osgforest.cpp
> b/examples/osgforest/osgforest.cpp
> index 5f569de66..d5eb2c0a6 100644
> --- a/examples/osgforest/osgforest.cpp
> +++ b/examples/osgforest/osgforest.cpp
> @@ -36,6 +36,7 @@
>  #include <osg/TexEnv>
>  #include <osg/VertexProgram>
>  #include <osg/FragmentProgram>
> +#include <osg/ClipNode>
>
>  #include <osgDB/ReadFile>
>  #include <osgDB/FileUtils>
> @@ -1487,7 +1488,11 @@ int main( int argc, char **argv )
>      viewer.addEventHandler(new
> osgGA::StateSetManipulator(viewer.getCamera()->getOrCreateStateSet()));
>
>      // add model to viewer.
> -    viewer.setSceneData( ttm->createScene(numTreesToCreate,
> maxNumTreesPerCell) );
> +       osg::Node *ttmnode = ttm->createScene(numTreesToCreate,
> maxNumTreesPerCell);
> +       osg::ClipNode *cn = new osg::ClipNode;
> +       cn->addClipPlane(new osg::ClipPlane(0, osg::Vec4d(1, 0, 0, -500)));
> +       cn->addChild(ttmnode);
> +    viewer.setSceneData( cn );
>
>
>      return viewer.run();
>
> ...the terrain and the trees are split by my additional clipping plane,
> except when the trees are instances; in that case they are drawn as
> normal.
>
> How can I make clipping planes work for  instanced rendering?
>
> Thanks!
>
> --
> Alberto
>
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