New OPenGL calls in the Example Program

• Some of this may be repeat from before, but we are ready for it now.
• A Vertex Buffer Object is a memory buffer on the video card.
  • A vbo contains data (vertices, colors, normals, ...)
  • The red book says there are many different types of VBOs
• A Vertex Array Object is an object that contains one or more VBOs
  • it is a complete object
  • But perhaps not final transformations
  • The red book says that there is only one type of VAO
• VAOs
  • void glGenVertexArrays(GLsizei n, GLuint * arrays)
    • n: the number of VAO names to generate
    • arrays: an allocated array in which to store the results.
    • Think of the return values as pointers. (Or indexes into a preallocated array)
  • void glDeleteVertexArrays(GLsizei n, const GLuint *arrays);
  • To do anything with a VAO you must make it active.
  • void glBindVertexArray(GLuint array);
    • array is the name of a previously allocated array.
    • 0 will break the binding with the current object.
    • A typical action will consist of

      Bind to a VAO
      perform a drawing action
      Unbind 
            

    • Much like we have been doing with glPushMatrix, glPopMatrix
    • The first time we bind to a name, a new object is actually created
    • Every other time, that object becomes the active object
  • GLboolean glIsVertexArray(GLuint array);
• VBOs
  • These actions are assocaited with the currently active VAO
  • So you need to have one active first.
  • void glGenBuffers(GLsizei n, GLuint * buffers);
    • Number of buffers to generate
    • Array to store the names.
  • void glBindBuffer( GLenum target, GLuint buffer);
    • Target:
      • GL_ARRAY_BUFFER for vertex data
      • GL_ELEMENT_ARRAY_BUFFER for index data
      • Others, follow link.
  • glDeleteBuffers, glIsBuffer as before.
  • glBufferData((GLenum target, GLsizeiptr size, const GLvoid * data, GLenum usage);
    • We have discussed this before.
    • Target as above.
    • Size in machine size
    • data, the base address of the array
    • usage (Static/Dynamic/Stream, Read/Copy/Draw)
• Associating the data in the VAO/VBO with variables in the shaders
  • They call this "shader plumbing"
  • glVertexAttribPointer(vPosition, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0)) connects positions in the current VBO with attribute vec4 vPosition; in the vertex shader
  • void glVertexAttribPointer(GLuint index, GLint size, GLenum type, GLboolean normalized, GLsizei stride, const GLvoid * pointer);
    • index: the index of the generic vertex attribute we will modify.
    • In the future, we will querry the shader for this position.
    • For now, we are using position 0
    • size: the number of vertices at teach point.
    • type: the type of the vertex data
    • normalized: should the data be normalized?
    • stride: as before, the space between instances (not the space from the end of one to the beginning of another, that would be gap)
    • pointer: This is where I ran into trouble before. In this case, it indicates that this is in a VBO and not an Array Buffer.
  • void glEnableVertexAttribArray( GLuint index);
    • Specifies the index of the generic vertex attribute to be enabled for the current VAO.

References

• Reference: VAO, VBO Turorial
• The Red Book