Vertex Buffer Objects

• Transfer data (points and attributes) to the GPU once.
• Generate Buffer names
  • glGenBuffers(GLsizeI n, GLuint * buffers)
  • Returns the "name" or ID of n different buffers in the buffer array positions.
  • I am reasonably sure that this is an index into a buffer table.
  • But you don't know that you will have sequential numbers
  • One buffer
• Bind the buffer to a use
  • glBindBuffer(GLenum target, GLuint buffer)
  • Target: described here is how the buffer will be used.
    • GL_ARRAY_BUFFER is a buffer for data, what we will use.
    • This mechanism can be used to transfer data back and forth from the CPU/CPU hence the many different options.
  • buffer is one of the buffers from the previous command.
  • This essentially tells OpenGL how you will be using the buffer.
  • I think of this as allocating a structure of the correct type on the remote machine.
    • If nothing is bound to the name, it is bound.
    • If something is bound, the binding is broken and rebound
• Associate data with the buffer
  • glBufferData(GLenum target, GLsizepter, size, const GLvoid * data, GLEnum usage)
  • target is a buffer id which has been allocated and bound
    • The same list as above. (GL_ARRAY_BUFFER)
  • size is the size, in bytes of the data to be transferred
  • data is a pointer to the data to be copied, or NULL
    • If NULL no data is copied
    • But space is allocated
  • usage is a hint on how the data will be used.
    • STREAM - written once, used a few times.
    • STATIC - written once, used many times.
    • DYNAMIC - modified frequently
    • DRAW - used for drawing
    • READ
    • WRITE
    • GL_STATIC_DRAW , GL_STREAM_READ
    • We probably want GL_STATIC_DRAW, or GL_STREAM_DRAW
    • Note that the incorrect setting will cause poor performance
  • If the buffer was pointing to an object, the object memory is deallocated.