Instancing and culling

[teub]

Hello,

While trying to use instancing in an efficient way, I keep coming to the same problem : I think there needs to be a way to specify a culling box for rendering visibility that isn't used for defining the shadow volume.

Imagine a use case for vegetation : you probably want to batch large areas of grass, but don't want these area to affect the shadow precision if the camera is looking at a small part of the terrain.

Currently one way to deal with it is to disable culling completely, but that leads to sending many useless triangles to the vertex shader.
Edit : another way I used to do to deal with those kind of large objects was to disable shadows casting. This isn't ideal either, and it doesn't work with some shadow techniques anyway.

I'm not sure I explained the issue properly ? or maybe I'm missing something.