Overview Function List GLOD Web Site


glodFillElements - Rather than drawing a patch, this places what would be drawn into the current OpenGL vertex/normal/color/texcoord and index arrays.


void glodFillElements(GLuint object_name, GLuint patch_name, GLenum type, GLvoid* out_elements)


object_name, patch_name
Selects the object and patch to read back.

Specifies the type of values in indices. May be GL_UNSIGNED_BYTE, GL_UNSIGNED_SHORT or GL_UNSIGNED_INT.

Specifies a pointer to the location where indices will be stored after this call. You must allocate this pointer yourself.


glodFillElements is used to ``see'' what GLOD will draw if you were to call glodDrawPatch. To read back the current state of an object using glodFillElements, you usually:

  • Call glodGetObjectParameter(obj, patch, GLOD_PATCH_SIZES, dst_arry) to obtain the number of vertices and indices (=triangles*3) that glodFillElements or glodDrawPatch will issue.

  • Allocate buffers for vertices and any other data that you want to read back according to the vertex count gotten from the previous call.

  • Set the vertx array state (glVertexPointer etc) to match your allocated buffers.

  • Allocate space for the indices that glodFillElements is going to use according to the index count from the first call

  • Call glodFillElements with this index array

When this call returns, the currently set array pointers will have been filled in with the current GLOD cut. It is critical that the buffers to which the pointers refer are large enough to accomodate the cut. Otherwise, memory corruption will occur.


The following code reads back the zero-th patch in object 0. It is assumed that the object consists of 1 patch and that the zero-th patch is named zero. If these assumptions do not hold, you will need an extra layer of indirection that uses the glodGetObjectParamiv GLOD_NUM_PATCHES and GLOD_PATCH_NAMES feature to make this code fully generic.

  // get the size of this patch
  GLfloat* vert_buf, *normal_buf; unsigned int* idx_buf;
  int numIndices,numVerts;
  int dims[2];
  glodGetObjectParamiv(0, GLOD_PATCH_SIZES, dims);
  numIndices = dims[0];
  numVerts   = dims[1]; // we ignore this value for glodFillArrays
  idx_buf = malloc(sizeof(unsigned int) idx_buf * numIndices);
  vert_buf = malloc(sizeof(float) * numVerts);
  normal_buf = malloc(sizeof(float) * numVerts);
  glVertexPointer(3, GL_FLOAT, 0, vert_buf);
  glNormalPointer(GL_FLOAT, 0, normal_buf);
  glFillElements(0, 0, GL_UNSIGNED_INT, idx_buf);
  // now, vert_buf and normal_buf contain a copy of 
  // object 0, patch 0's current geometry
  // and idx_buf contains triples of triangle indices into these
  // arrays just like with glDrawElements


GLOD_INVALID_NAME is generated if an object of the specified name does not exist
GLOD_INVALID_STATE is generated if the object has not been built yet.
GLOD_INVALID_PATCH is generated if the object does not have a patch of the specified name.

Last modified: 06/10/04 06:32:24 PM