Hi Claudio, Welcome to the OSG community. For your first post you sure are diving into an advanced topic :-)
Conventionally one would do clipping using gl_ClipPlane, this is set by osg::ClipPlane state attribute and osg::ClipNode to place one or more ClipPlane in a final position in space, I think OpenGL implementations provide at least 6 clip planes, but It's while since I've head my head deep in OpenGL as I'm mostly working with Vulkan these days. There is a hard limit though that is driver/hardware dependent. This type of clipping gets applied during the traseration step just prior to the fragment shader. It can be used with fixed function and shader pipelines. >From your description it sounds like something custom will be best, which in essence would be to use a fragment shader test to discard/fade out fragments based on some combination of uniform or vertex attribute settings. Is the clipping always going to base on a horizontal plane? If so then you just need to encode the height to clip at for each object via a uniform or more efficiently with a vertex attribute bound with BIND_OVERALL. Uniforms have a higher overhead than vertex attributes in OSG/OpenGL so general best used for rarely changing values, with values that change with high frequency i.e. different for each object using vertex attributes will be more efficient. Cheers, Robert.
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