OpenGL - Will using multiple VBO's slow down rendering?

Question

I am rendering some meshes (sometimes upwards of 500) and I wanted to know the best way to approach this. Would it be pointless to create 500 VBOs and then if they pass the frustum and visibility tests, render them. Is there a more efficient way to do this? I am looking to maximize performance.

Answer 1

To answer your question, yes, many VBOs will slow things down. More polys will usually slow down the render, but more draw calls has a much greater hit. You want to minimize state changes and draws, as well as the number of buffers you have (and memory use).

I would suggest first looking at the buffers and figuring out how many you need. If you can batch/instance geometry, merge static geometry into a single buffer, reuse buffer more efficiently, etc.

Once you've cut the buffers down to the minimum possible, you'll want to use culling of multiple sorts. Visibility, both by frustrum (perhaps in an octree) and occlusion, can provide a significant performance boost. The main idea is to disqualify the geometry as fast and simply as possible, so you start with rough tests (octree), then somewhat more detailed (perhaps an AABB and/or simplified hull), then occlusion, then actually draw.

Here's a good article on frustrum culling, which touches a bit on quadtrees (and by extension, octrees). Diagrams, explanations and some sample code.

OpenGL occlusion culling articles seem a bit less common, although this one from GPU Gems might be a good starting place.