(new) CUDA IoU for 3D boxes

Summary: CUDA implementation of 3D bounding box overlap calculation.

Reviewed By: gkioxari

Differential Revision: D31157919

fbshipit-source-id: 5dc89805d01fef2d6779f00a33226131e39c43ed

Author: nikhilaravi

pytorch3d/csrc/iou_box3d/iou_box3d.cu

@@ -0,0 +1,176 @@
+/*
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <ATen/ATen.h>
+#include <ATen/cuda/CUDAContext.h>
+#include <c10/cuda/CUDAGuard.h>
+#include <math.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <thrust/device_vector.h>
+#include <thrust/tuple.h>
+#include "iou_box3d/iou_utils.cuh"
+#include "utils/pytorch3d_cutils.h"
+
+// Parallelize over N*M computations which can each be done
+// independently
+__global__ void IoUBox3DKernel(
+    const at::PackedTensorAccessor64<float, 3, at::RestrictPtrTraits> boxes1,
+    const at::PackedTensorAccessor64<float, 3, at::RestrictPtrTraits> boxes2,
+    at::PackedTensorAccessor64<float, 2, at::RestrictPtrTraits> vols,
+    at::PackedTensorAccessor64<float, 2, at::RestrictPtrTraits> ious) {
+  const size_t N = boxes1.size(0);
+  const size_t M = boxes2.size(0);
+
+  const size_t tid = blockIdx.x * blockDim.x + threadIdx.x;
+  const size_t stride = gridDim.x * blockDim.x;
+
+  for (size_t i = tid; i < N * M; i += stride) {
+    const size_t n = i / M; // box1 index
+    const size_t m = i % M; // box2 index
+
+    // Convert to array of structs of face vertices i.e. effectively (F, 3, 3)
+    // FaceVerts is a data type defined in iou_utils.cuh
+    FaceVerts box1_tris[NUM_TRIS];
+    FaceVerts box2_tris[NUM_TRIS];
+    GetBoxTris(boxes1[n], box1_tris);
+    GetBoxTris(boxes2[m], box2_tris);
+
+    // Calculate the position of the center of the box which is used in
+    // several calculations. This requires a tensor as input.
+    const float3 box1_center = BoxCenter(boxes1[n]);
+    const float3 box2_center = BoxCenter(boxes2[m]);
+
+    // Convert to an array of face vertices
+    FaceVerts box1_planes[NUM_PLANES];
+    GetBoxPlanes(boxes1[n], box1_planes);
+    FaceVerts box2_planes[NUM_PLANES];
+    GetBoxPlanes(boxes2[m], box2_planes);
+
+    // Get Box Volumes
+    const float box1_vol = BoxVolume(box1_tris, box1_center, NUM_TRIS);
+    const float box2_vol = BoxVolume(box2_tris, box2_center, NUM_TRIS);
+
+    // Tris in Box1 intersection with Planes in Box2
+    // Initialize box1 intersecting faces. MAX_TRIS is the
+    // max faces possible in the intersecting shape.
+    // TODO: determine if the value of MAX_TRIS is sufficient or
+    // if we should store the max tris for each NxM computation
+    // and throw an error if any exceeds the max.
+    FaceVerts box1_intersect[MAX_TRIS];
+    for (int j = 0; j < NUM_TRIS; ++j) {
+      // Initialize the faces from the box
+      box1_intersect[j] = box1_tris[j];
+    }
+    // Get the count of the actual number of faces in the intersecting shape
+    int box1_count = BoxIntersections(box2_planes, box2_center, box1_intersect);
+
+    // Tris in Box2 intersection with Planes in Box1
+    FaceVerts box2_intersect[MAX_TRIS];
+    for (int j = 0; j < NUM_TRIS; ++j) {
+      box2_intersect[j] = box2_tris[j];
+    }
+    const int box2_count =
+        BoxIntersections(box1_planes, box1_center, box2_intersect);
+
+    // If there are overlapping regions in Box2, remove any coplanar faces
+    if (box2_count > 0) {
+      // Identify if any triangles in Box2 are coplanar with Box1
+      Keep tri2_keep[MAX_TRIS];
+      for (int j = 0; j < MAX_TRIS; ++j) {
+        // Initialize the valid faces to be true
+        tri2_keep[j].keep = j < box2_count ? true : false;
+      }
+      for (int b1 = 0; b1 < box1_count; ++b1) {
+        for (int b2 = 0; b2 < box2_count; ++b2) {
+          const bool is_coplanar =
+              IsCoplanarFace(box1_intersect[b1], box2_intersect[b2]);
+          if (is_coplanar) {
+            tri2_keep[b2].keep = false;
+          }
+        }
+      }
+
+      // Keep only the non coplanar triangles in Box2 - add them to the
+      // Box1 triangles.
+      for (int b2 = 0; b2 < box2_count; ++b2) {
+        if (tri2_keep[b2].keep) {
+          box1_intersect[box1_count] = box2_intersect[b2];
+          // box1_count will determine the total faces in the
+          // intersecting shape
+          box1_count++;
+        }
+      }
+    }
+
+    // Initialize the vol and iou to 0.0 in case there are no triangles
+    // in the intersecting shape.
+    float vol = 0.0;
+    float iou = 0.0;
+
+    // If there are triangles in the intersecting shape
+    if (box1_count > 0) {
+      // The intersecting shape is a polyhedron made up of the
+      // triangular faces that are all now in box1_intersect.
+      // Calculate the polyhedron center
+      const float3 poly_center = PolyhedronCenter(box1_intersect, box1_count);
+      // Compute intersecting polyhedron volume
+      vol = BoxVolume(box1_intersect, poly_center, box1_count);
+      // Compute IoU
+      iou = vol / (box1_vol + box2_vol - vol);
+    }
+
+    // Write the volume and IoU to global memory
+    vols[n][m] = vol;
+    ious[n][m] = iou;
+  }
+}
+
+std::tuple<at::Tensor, at::Tensor> IoUBox3DCuda(
+    const at::Tensor& boxes1, // (N, 8, 3)
+    const at::Tensor& boxes2) { // (M, 8, 3)
+  // Check inputs are on the same device
+  at::TensorArg boxes1_t{boxes1, "boxes1", 1}, boxes2_t{boxes2, "boxes2", 2};
+  at::CheckedFrom c = "IoUBox3DCuda";
+  at::checkAllSameGPU(c, {boxes1_t, boxes2_t});
+  at::checkAllSameType(c, {boxes1_t, boxes2_t});
+
+  // Set the device for the kernel launch based on the device of boxes1
+  at::cuda::CUDAGuard device_guard(boxes1.device());
+  cudaStream_t stream = at::cuda::getCurrentCUDAStream();
+
+  TORCH_CHECK(boxes2.size(2) == boxes1.size(2), "Boxes must have shape (8, 3)");
+
+  TORCH_CHECK(
+      (boxes2.size(1) == 8) && (boxes1.size(1) == 8),
+      "Boxes must have shape (8, 3)");
+
+  const int64_t N = boxes1.size(0);
+  const int64_t M = boxes2.size(0);
+
+  auto vols = at::zeros({N, M}, boxes1.options());
+  auto ious = at::zeros({N, M}, boxes1.options());
+
+  if (vols.numel() == 0) {
+    AT_CUDA_CHECK(cudaGetLastError());
+    return std::make_tuple(vols, ious);
+  }
+
+  const size_t blocks = 512;
+  const size_t threads = 256;
+
+  IoUBox3DKernel<<<blocks, threads, 0, stream>>>(
+      boxes1.packed_accessor64<float, 3, at::RestrictPtrTraits>(),
+      boxes2.packed_accessor64<float, 3, at::RestrictPtrTraits>(),
+      vols.packed_accessor64<float, 2, at::RestrictPtrTraits>(),
+      ious.packed_accessor64<float, 2, at::RestrictPtrTraits>());
+
+  AT_CUDA_CHECK(cudaGetLastError());
+
+  return std::make_tuple(vols, ious);
+}

pytorch3d/csrc/iou_box3d/iou_box3d.h

@@ -26,12 +26,23 @@ std::tuple<at::Tensor, at::Tensor> IoUBox3DCpu(
     const at::Tensor& boxes1,
     const at::Tensor& boxes2);
 
+// CUDA implementation
+std::tuple<at::Tensor, at::Tensor> IoUBox3DCuda(
+    const at::Tensor& boxes1,
+    const at::Tensor& boxes2);
+
 // Implementation which is exposed
 inline std::tuple<at::Tensor, at::Tensor> IoUBox3D(
     const at::Tensor& boxes1,
     const at::Tensor& boxes2) {
   if (boxes1.is_cuda() || boxes2.is_cuda()) {
-    AT_ERROR("GPU support not implemented");
+#ifdef WITH_CUDA
+    CHECK_CUDA(boxes1);
+    CHECK_CUDA(boxes2);
+    return IoUBox3DCuda(boxes1.contiguous(), boxes2.contiguous());
+#else
+    AT_ERROR("Not compiled with GPU support.");
+#endif
   }
   return IoUBox3DCpu(boxes1.contiguous(), boxes2.contiguous());
 }

pytorch3d/csrc/iou_box3d/iou_box3d_cpu.cpp

@@ -79,7 +79,7 @@ std::tuple<at::Tensor, at::Tensor> IoUBox3DCpu(
         std::fill(tri2_keep.begin(), tri2_keep.end(), 1);
         for (int b1 = 0; b1 < box1_intersect.size(); ++b1) {
           for (int b2 = 0; b2 < box2_intersect.size(); ++b2) {
-            bool is_coplanar =
+            const bool is_coplanar =
                 IsCoplanarFace(box1_intersect[b1], box2_intersect[b2]);
             if (is_coplanar) {
               tri2_keep[b2] = 0;