TheRock/rocm-libraries/projects/rocthrust/examples/weld_vertices.cu

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#include <thrust/binary_search.h>
#include <thrust/device_vector.h>
#include <thrust/remove.h>
#include <thrust/sort.h>
#include <thrust/unique.h>

#include <iostream>

/*
 * This example "welds" triangle vertices together by taking as
 * input "triangle soup" and eliminating redundant vertex positions
 * and shared edges.  A connected mesh is the result.
 *
 *
 * Input: 9 vertices representing a mesh with 3 triangles
 *
 *  Mesh              Vertices
 *    ------           (2)      (5)--(4)    (8)
 *    | \ 2| \          | \       \   |      | \
 *    |  \ |  \   <->   |  \       \  |      |  \
 *    | 0 \| 1 \        |   \       \ |      |   \
 *    -----------      (0)--(1)      (3)    (6)--(7)
 *
 *   (vertex 1 equals vertex 3, vertex 2 equals vertex 5, ...)
 *
 * Output: mesh representation with 5 vertices and 9 indices
 *
 *  Vertices            Indices
 *   (1)--(3)            [(0,2,1),
 *    | \  | \            (2,3,1),
 *    |  \ |  \           (2,4,3)]
 *    |   \|   \
 *   (0)--(2)--(4)
 */

// define a 2d float vector
using vec2 = thrust::tuple<float, float>;

int main(void)
{
  // allocate memory for input mesh representation
  thrust::device_vector<vec2> input(9);

  input[0] = vec2(0, 0); // First Triangle
  input[1] = vec2(1, 0);
  input[2] = vec2(0, 1);
  input[3] = vec2(1, 0); // Second Triangle
  input[4] = vec2(1, 1);
  input[5] = vec2(0, 1);
  input[6] = vec2(1, 0); // Third Triangle
  input[7] = vec2(2, 0);
  input[8] = vec2(1, 1);

  // allocate space for output mesh representation
  thrust::device_vector<vec2> vertices = input;
  thrust::device_vector<unsigned int> indices(input.size());

  // sort vertices to bring duplicates together
  thrust::sort(vertices.begin(), vertices.end());

  // find unique vertices and erase redundancies
  vertices.erase(thrust::unique(vertices.begin(), vertices.end()), vertices.end());

  // find index of each input vertex in the list of unique vertices
  thrust::lower_bound(vertices.begin(), vertices.end(), input.begin(), input.end(), indices.begin());

  // print output mesh representation
  std::cout << "Output Representation" << std::endl;
  for (size_t i = 0; i < vertices.size(); i++)
  {
    vec2 v = vertices[i];
    std::cout << " vertices[" << i << "] = (" << thrust::get<0>(v) << "," << thrust::get<1>(v) << ")" << std::endl;
  }
  for (size_t i = 0; i < indices.size(); i++)
  {
    std::cout << " indices[" << i << "] = " << indices[i] << std::endl;
  }

  return 0;
}