Example/Program Interface Uniforms In Blocks

Iteration over all uniforms within each uniform block.

GLint numBlocks = 0;
glGetProgramInterfaceiv(prog, GL_UNIFORM_BLOCK, GL_ACTIVE_RESOURCES, &numBlocks);
const GLenum blockProperties[1] = {GL_NUM_ACTIVE_VARIABLES};
const GLenum activeUnifProp[1] = {GL_ACTIVE_VARIABLES};
const GLenum unifProperties[3] = {GL_NAME_LENGTH​, GL_TYPE​, GL_LOCATION};

for(int blockIx = 0; blockIx < numBlocks; ++blockIx)
{
  GLint numActiveUnifs = 0;
  glGetProgramResourceiv(prog, GL_UNIFORM_BLOCK, blockIx, 1, blockProperties, 1, NULL, numActiveUnifs);

  if(!numActiveUnifs)
    continue;

  std::vector<GLint> blockUnifs(numActiveUnifs);
  glGetProgramResourceiv(prog, GL_UNIFORM_BLOCK, blockIx, 1, activeUnifProp, numActiveUnifs, NULL, &blockUnifs[0]);

  for(int unifIx = 0; unifIx < numActiveUnifs; ++unifIx)
  {
    GLint values[3];
    glGetProgramResourceiv(prog, GL_UNIFORM, blockUnifs[unifIx], 3, unifProperties, 3, NULL, values);

    //Get the name. Must use a std::vector rather than a std::string for C++03 standards issues.
    //C++11 would let you use a std::string directly.
    std::vector<char> nameData(values[0]);
    glGetProgramResourceName(prog, GL_UNIFORM, blockUnifs[unifIx], nameData.size(), NULL, &nameData[0]);
    std::string name(nameData.begin(), nameData.end() - 1);
  }
}