def backward(ctx, grad_dists):
grad_dists = grad_dists.contiguous()
points, tris, idxs = ctx.saved_tensors
grad_points, grad_tris = _C.face_point_dist_backward(
points, tris, idxs, grad_dists
)
return grad_points, None, grad_tris, None, None
def test_face_point_distance(self):
"""
Test CUDA implementation for FacePointDistanceForward
& FacePointDistanceBackward
"""
device = get_random_cuda_device()
N, V, F, P = 4, 32, 16, 24
meshes, pcls = self.init_meshes_clouds(N, V, F, P, device=device)
# make points packed a leaf node
points_packed = pcls.points_packed().detach().clone() # (P, 3)
points_first_idx = pcls.cloud_to_packed_first_idx()
# make edges packed a leaf node
verts_packed = meshes.verts_packed()
faces_packed = verts_packed[meshes.faces_packed()] # (T, 3, 3)
faces_packed = faces_packed.clone().detach()
faces_first_idx = meshes.mesh_to_faces_packed_first_idx()
max_f = meshes.num_faces_per_mesh().max().item()
# leaf nodes
points_packed.requires_grad = True
faces_packed.requires_grad = True
grad_dists = torch.rand(
(faces_packed.shape[0],), dtype=torch.float32, device=device
)
# Cuda Implementation: forward
dists_cuda, idx_cuda = _C.face_point_dist_forward(
points_packed, points_first_idx, faces_packed, faces_first_idx, max_f
)
# Cuda Implementation: backward
grad_points_cuda, grad_faces_cuda = _C.face_point_dist_backward(
points_packed, faces_packed, idx_cuda, grad_dists
)
# Cpu Implementation: forward
dists_cpu, idx_cpu = _C.face_point_dist_forward(
points_packed.cpu(),
points_first_idx.cpu(),
faces_packed.cpu(),
faces_first_idx.cpu(),
max_f,
)
# Cpu Implementation: backward
grad_points_cpu, grad_faces_cpu = _C.face_point_dist_backward(
points_packed.cpu(), faces_packed.cpu(), idx_cpu, grad_dists.cpu()
)
# Naive Implementation: forward
faces_list = packed_to_list(faces_packed, meshes.num_faces_per_mesh().tolist())
dists_naive = []
for i in range(N):
points = pcls.points_list()[i]
tris = faces_list[i]
dists_temp = torch.zeros(
(tris.shape[0], points.shape[0]), dtype=torch.float32, device=device
)
for t in range(tris.shape[0]):
for p in range(points.shape[0]):
dist = self._point_to_tri_distance(points[p], tris[t])
dists_temp[t, p] = dist
# torch.min() doesn't necessarily return the first index of the
# smallest value, our warp_reduce does. So it's not straightforward
# to directly compare indices, nor the gradients of grad_tris which
# also depend on the indices of the minimum value.
# To be able to compare, we will compare dists_temp.min(1) and
# then feed the cuda indices to the naive output
start = faces_first_idx[i]
end = faces_first_idx[i + 1] if i < N - 1 else faces_packed.shape[0]
min_idx = idx_cuda.cpu()[start:end] - points_first_idx[i].cpu()
iidx = torch.arange(tris.shape[0], device=device)
min_dist = dists_temp[iidx, min_idx]
dists_naive.append(min_dist)
dists_naive = torch.cat(dists_naive)
# Compare
self.assertClose(dists_naive.cpu(), dists_cuda.cpu())
self.assertClose(dists_naive.cpu(), dists_cpu)
# Naive Implementation: backward
dists_naive.backward(grad_dists)
grad_points_naive = torch.cat([cloud.grad for cloud in pcls.points_list()])
grad_faces_naive = faces_packed.grad
# Compare
self.assertClose(grad_points_naive.cpu(), grad_points_cuda.cpu(), atol=1e-7)
self.assertClose(grad_faces_naive.cpu(), grad_faces_cuda.cpu(), atol=5e-7)
self.assertClose(grad_points_naive.cpu(), grad_points_cpu, atol=1e-7)
self.assertClose(grad_faces_naive.cpu(), grad_faces_cpu, atol=5e-7)