Optimising Many glDrawArraysInstanced Calls

[Dark_Photon]

@Vercidium

1. Is there another glDraw*Indirect or glMultiDraw* approach I can take, or
2. should I store the data for all of my chunks in one large VBO and render it using Gl.DrawArraysIndirect?

The latter. This works great. And ensures no state changes between instances.

If you’re CPU/submission limited, just getting rid of all those buffer binds is likely to net you a nice perf improvement. But for even more…

You probably would anyway, but be sure you use the instanced subdraw feature in MultiDraw Indirect (MDI) – see instanceCount and baseInstance here:

• glMultiDrawArraysIndirect
• glMultiDrawElementsIndirect

That is, one subdraw record per model (all instances), not one subdraw record per model instance.

Why? On some GPUs/drivers such as NVIDIAs, the vertex work is packed more efficiently with instanced rendering, particularly for models with few verts (“small models”), yielding higher GPU utilization and faster drawing.

For way more info on this than you’re interested in, see:

GPU vertex dispatch for MultiDrawIndirect and/or Instanced draw calls

Doing some reading, I see indications (but not outright statements) in GPU vendor documentation that GPUs do not pack: vertices across different instances in an instanced draw, nor vertices across different draws in a MultiDrawIndirect draw call into shared thread groups (warps or wavefronts). I also find devs on the net saying that GPUs do not do this, but without a pointer to vendor docs as the source. My question is, does anyone know whether this is (or is not) the case? (If so, I gue…