Non-interleaved vertex buffers DirectX11

Question

If my vertex positions are shared, but my normals and UVs are not (to preserve hard edges and the likes), is it possible to use non-interleaved buffers in DirectX11 to solve

Answer 1

Interleaved/Separate will mostly affect your Input Assembler stage (GPU side).

A perfect scenario for Interleaved is when your Buffer memory arrangement perfectly fits your vertex shader input. So your Input assembler can simply fetch the data.

In that case you'll be totally fine with interleaved, even tho testing with a large model (two versions of the same data, one interleaved, one separate), TimeStamp query didn't reported any major difference (some pretty minimal vertex processing and basic pixel shader).

Now having separate buffers makes it much easier to fine tune in case you use your geometry in different contexts.

Let's say you have Position/Normals/UV (like in your case).

Now you also have a shader in your pipeline that only requires Position (Shadow Map would be a pretty good example).

With separate buffers, you can simply create a new input layout which contains position only, And bind that buffer instead. Your IA stage has only to load that buffer. Best of all you can even do that dynamically using shader reflection.

If you bind Interleaved data, you will have some overhead due to the fact it has to load with a stride.

When I tested that one I had about 20% gain using Separate instead of Interleaved, which can be quite decent, but since this type of processing can be largely architecture dependent, don't take it for granted (NVidia 740M for testing).

So simply put, profile (a lot), and check which gives you the best balance between your GPU and CPU loads.

Please also note that the overhead from Input Assembler will decrease from the complexity of your shader, if you apply some heavy calculations + add some tessellation + some decent shading, the time difference between interleaved/non interleaved will become progressively meaningless.