Hi All,
I am implementing a simple bounding box algorithm on opencl and I have problem with the computations.
I have a set of vertices which I pass into the kernel and I compute the bounding box accordingly. I also pass in another array just to read back the vertices back
from the kernel to find that they are all different. I am running on WinXP with Quadro FX 570M and 197.15 (Nvidia Driver).
The code for the C part is this.
Code :
  float bbox[8], results[8];
  memset(results, 0, 8 * sizeof(float));
 
  bbox[0] = (float)mesh->vertex[0].pt[0]; bbox[4] = (float)mesh->vertex[0].pt[0];
  bbox[1] = (float)mesh->vertex[0].pt[1]; bbox[5] = (float)mesh->vertex[0].pt[1];
  bbox[2] = (float)mesh->vertex[0].pt[2]; bbox[6] = (float)mesh->vertex[0].pt[2];
 
  // GPU Calculation
  float* vertices = static_cast<float *>(malloc(4 * mesh->vertex_count * sizeof(float)));
  float* fnew_verts = static_cast<float *>(malloc(4 * mesh->vertex_count * sizeof(float)));
 
  memset(vertices, 0, 4 * mesh->vertex_count * sizeof(float));
  memset(fnew_verts, 0, 4 * mesh->vertex_count * sizeof(float));
 
  float* vertex = vertices;
  for (int i = 0; i < mesh->vertex_count; i++)
  {
    *vertex++ = (float)mesh->vertex[i].pt[0];
    *vertex++ = (float)mesh->vertex[i].pt[1];
    *vertex++ = (float)mesh->vertex[i].pt[2];
    *vertex++;
  }
 
  ShaderManager* shm = ShaderManager::Instance();
 
  cl_int err;
  cl_mem vertices_mem, bbox_mem, new_verts;
  vertices_mem = clCreateBuffer(shm->opencl_context(), CL_MEM_READ_ONLY, 4 * mesh->vertex_count * sizeof(float), NULL, NULL);
  err = clEnqueueWriteBuffer(shm->opencl_command_queue(), vertices_mem, CL_TRUE, 0, 4 * mesh->vertex_count * sizeof(float), 
                             (void *)vertices, 0, NULL, NULL);
 
  bbox_mem = clCreateBuffer(shm->opencl_context(), CL_MEM_READ_WRITE, 8 * sizeof(float), NULL, NULL);
  err = clEnqueueWriteBuffer(shm->opencl_command_queue(), bbox_mem, CL_TRUE, 0, 8 * sizeof(float), (void *)bbox, 0, NULL, NULL);
 
  new_verts = clCreateBuffer(shm->opencl_context(), CL_MEM_WRITE_ONLY, 4 * mesh->vertex_count * sizeof(float), NULL, NULL);
 
  clFinish(shm->opencl_command_queue());
 
  err = clSetKernelArg(shm->opencl_kernel(), 0, sizeof(cl_mem), &vertices_mem);
  err |= clSetKernelArg(shm->opencl_kernel(), 1, sizeof(cl_mem), &bbox_mem);
  err |= clSetKernelArg(shm->opencl_kernel(), 2, sizeof(cl_mem), &new_verts);
 
  size_t global_work_size = mesh->vertex_count;
  err = clEnqueueNDRangeKernel(shm->opencl_command_queue(), shm->opencl_kernel(), 1, NULL, 
                               &global_work_size, NULL, 0, NULL, NULL);
 
#pragma warning(disable:4189)
  const char* str = errorString(err);
  clFinish(shm->opencl_command_queue());
 
 
  err = clEnqueueReadBuffer(shm->opencl_command_queue(), bbox_mem, CL_TRUE, 0, 8 * sizeof(float), 
                            results, 0, NULL, NULL);
  err = clEnqueueReadBuffer(shm->opencl_command_queue(), new_verts, CL_TRUE, 0, 4 * mesh->vertex_count * sizeof(float),
                            fnew_verts, 0, NULL, NULL);
 
  clFinish(shm->opencl_command_queue());
 
  // Verify with input data
  for (int i = 0; i < 4 * mesh->vertex_count; i++)
    assert(fnew_verts[i] == vertices[i]);
 
  for (int i = 0; i < mesh->vertex_count; i++)
  {
    mesh->vertex[i].pt[0] = (double)(fnew_verts[0]);
    mesh->vertex[i].pt[1] = (double)(fnew_verts[1]);
    mesh->vertex[i].pt[2] = (double)(fnew_verts[2]);
    fnew_verts += 4;
  }
 
  free(vertices);

The kernel is defined like this as follows:
Code :
 __kernel void bound_mesh(__global float4* vertices, __global float4* bbox, __global float4 new_verts)
 {
  int gid = get_global_id(0);
 
  if (vertices[gid].x < bbox[0].x)
    bbox[0].x = vertices[gid].x;
 
  if (vertices[gid].y < bbox[0].y)
    bbox[0].y = vertices[gid].y;
 
  if (vertices[gid].z < bbox[0].z)
    bbox[0].z = vertices[gid].z;
 
  if (vertices[gid].x > bbox[1].x)
    bbox[1].x = vertices[gid].x;
 
  if (vertices[gid].y > bbox[1].y)
    bbox[1].y = vertices[gid].y;
 
  if (vertices[gid].z > bbox[2].z)
    bbox[1].z = vertices[gid].z;
 
  new_verts[gid = vertices[gid];
 
  bbox[0].w = -1.0; bbox[1].w = -1.0;
 }

So new_verts should atleast give me the correct vertices considering I am assigning them the same value for the vertices.
So neither the bounding box nor the new_verts has the correct values in them. Any suggestions as to what I might be doing wrong.
Thanks for your help.