I have a similar geometry culling question to this, but my situation is more about culling geometries outside the viewport.
In my case I have a custom geometry, let's say it's a 2d polyline with fixed points for simplicity. (In reality it's a bit more complex than this, the vertices require some computation and sometimes there are faces but rarely they overlap so depth-based culling is of limited help.)
I have these in a device PolyLine *buffer and encode a draw call with
If you're zoomed in very closely on this scene, possibly most of the geometry is well outside the viewing area. Or in some cases geometry could be partially visible (such as start->a), but not the rest (a->b and b->end). For geometries with more vertices it is more likely that a very small number of the full geometry is visible.
Often, I don't cull this at all. Other times if the shader is more expensive I will do some kind of bailout check on the whole instance as a prelude in the vertex shader. If the instance is invisible, I choose a vertex output position with some constant value outside the viewport.
What is the best practice for avoiding unnecessary work here? Should I be indirectly encoding draws for each visible instance, or does that introduce more overhead? Is there a best-practice way to tell Metal that a vertex (or an instance) can be discarded or is picking some faraway position ok?
In my case I have a custom geometry, let's say it's a 2d polyline with fixed points for simplicity. (In reality it's a bit more complex than this, the vertices require some computation and sometimes there are faces but rarely they overlap so depth-based culling is of limited help.)
Code Block typedef struct PolyLine { simd_float2 start; simd_float2 a; simd_float2 b; simd_float2 end; }
I have these in a device PolyLine *buffer and encode a draw call with
Code Block _commandEncoder.drawPrimitives(type: .lineStrip, vertexStart: 0, vertexCount: 4, instanceCount: 50000)
If you're zoomed in very closely on this scene, possibly most of the geometry is well outside the viewing area. Or in some cases geometry could be partially visible (such as start->a), but not the rest (a->b and b->end). For geometries with more vertices it is more likely that a very small number of the full geometry is visible.
Often, I don't cull this at all. Other times if the shader is more expensive I will do some kind of bailout check on the whole instance as a prelude in the vertex shader. If the instance is invisible, I choose a vertex output position with some constant value outside the viewport.
What is the best practice for avoiding unnecessary work here? Should I be indirectly encoding draws for each visible instance, or does that introduce more overhead? Is there a best-practice way to tell Metal that a vertex (or an instance) can be discarded or is picking some faraway position ok?
