CODEWITHSUNDEEP
cudagpuindicesnormals
dhan
dhan

Reputation: 63

c opengl: can i calculate normals in gpu? (CUDA)

I am trying to access last and next indices coordinates inside the kernel.

ex: int idx = blockIdx.x * blockDim.x + threadIdx.x;

then pos[idx].x, pos[idx].y, pos[idx].z would give current coordinates of a point. but cannot access other two. I am trying to calculate the normals of the changing triangle in GPU level using CUDA.

Upvotes: 2

Views: 781

Answers (2)

axon
axon

Reputation: 1200

How easily normals can be computed on the GPU depends on the mesh topology.

It is easy to compute normals for a mesh with triangle-list topology: Use one GPU thread per triangle. This results in highly regular reads and writes and will work for any valid configuration of blocks and threads in CUDA. Unfortunately, triangle-list topology isn't very useful (for starters, it will be flat-shaded unless some additional processing is employed).

It is [much] harder to compute normals for a mesh with triangle-strip topology (which is commonly used). The problem is that vertices are used in multiple triangles and therefore you must accumulate a [weighted] average for each vertex-normal by combining multiple triangle-normals. Using one GPU thread per triangle means that multiple vert-norms will be affected from multiple GPU threads "simultaneously". Alternatively, using one GPU thread per vertex means that a list of triangles that reference that vertex are needed, then the triangles need to be read (pairs of additional verts) so that the vert-norm can be computed... which is difficult, but not impossible.

Finally, if your model uses indexed vertices, this will impose an additional [semi-random] look-up which may cause problems. This problem can be addressed with spatial partitioning.

Upvotes: 1

Martin Beckett
Martin Beckett

Reputation: 96167

You can still do idx+1, idx+2, the GPU has access to all the shared memory

For best efficency you have to be a little carefull about how you divide up the job into blocks/threads etc so that memory for nearby points is on the same core.

Upvotes: 0

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