Question

Is there a faster way to set the vertex buffer data than SetVertexBuffer? It seems to cause massive performance drops and is really slow :/.

Answer 1

SetVertexBuffer should be the fastest way of assigning vertex data as this method is directly accessing the DirectX 9 API.

As far as I know (working with DX11) there is no other way of assigning vertex data. Even when you call DrawUserPrimitives or DrawUserIndexedPrimitives a buffer is created and then sent to the device. The difference here is that this buffer will be created for every draw call, as you could have changed the data in the meantime, so it should be even slower.

Make sure it is actually the SetVertexBuffer call that is slowing down your application. If it is you are maybe just sending a lot of data to the device, which should take a while. But I cannot tell without code.

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Many individual calls to SetVertexBuffer will in fact slow down the application. And sending two buffers to the device will most likely be slower than a single buffer containing the combined data.
Some tips:

• Keep the total number of buffers down. Use index and vertex offsets to draw only certain segments of the buffer.
• Avoid too many switches between buffers. (This is a general guideline for everything you send to the device. Avoid change of state.)
• Use static buffers where possible.
• If you really need dynamic meshes try to separate them from the static data for optimized caching. (Credits to A-Type, see comments)

But as always, performance in 3D applications is a fuzzy subject. Soon there could be other bottlenecks (shaders, textures, etc.) and you may have to break with the above guidelines.