OpenGL single VBO vs multiple VBOs

Question

Currently, in my rendering engine, I have a VBO for each mesh data (1 VBO for vertices, 1 VBO for normals, 1 VBO for texture coordinates, 1 VBO for tangents and 1 VBO for bitangents) and all of them are bound together with a VAO.

I'm now thinking about changing the system to hold a single VBO containing all the mesh data (vertices, normals, etc.) but how mush will I gain from this? Speaking about speed and utility (because I may not have all the data and provide only vertices and normals if my mesh isn't textured).

Answer 1

You'll be seeking to reduce overall memory bandwidth. If your buffer object contains all of your attributes interleaved together then that means that your entire array object references only one single contiguous section of memory. Which is much easier for a memory subsystem to cache. It's exactly the same principle as for CPUs — the more local consecutive memory accesses are, the faster they're likely to be.

There is also a potential detriment: the general rule is that you should align your elements to whichever is the greater of the size of the element and four bytes. Which leads to some wasted space. But the benefit almost always outweighs the detriment.

Obviously the only thing that will be affected is the time the GPU takes to fetch the vertices. If you're tessellation or fill bound you won't immediately see any improvement.