Should unbind buffers?

Question

I'm making some tests with OpenGL ES 2 and got some questions, my current program is like that:

Init
-------
-> create index buffer
-> fill index buffer glBufferData …
-> create vertex buffer
-> fill vertex buffer glBufferData …

Draw
-------
 1. Apply vertex buffer

    -> Bind VAO
       -> bind vertex buffer
          - enable attributs (glVertexPointer, …)
       -> unbind vertex buffer
    -> Unbind VAO
    -> Bind VAO

 3. Apply index buffer
 4. Draw

The problem

The given code crash, after some researches, I've understood why: I need to unbind my index buffer in init part (after "fill index buffer glBufferData") or unbind it before the first "Bind VAO"

My questions are:

• Can I put my index buffer in VAO (VAO stock index buffer?)?
• Did I have to unbind buffers after each update (glBufferData)?

In my application I've got some buffers who are updated on each frame (Exemple: Particles) so I've got an OpenGL stack like that:

-> bind buffer 1
-> update buffer 1
-> close buffer 1
-> bind buffer 1
-> draw

First 3 lines update the Vertex buffer, the two last draw object, that should be something like that:

-> bind buffer 1
-> update buffer 1
-> draw

Thanks

Answer 1

You seem to be doing a lot on unnecessary binding/unbinding. If you are using a VAO, then you should only bind the VAO when you set it up and when drawing the geometry. You only bind the VBO/IBO again when you need to update them.

After drawing or updating a buffer, you don't necessarily have to unbind it, though it might be a good idea to do so to avoid accidental writes to buffers that were left bound.

Now taking your fist sequence of operations, this is the overall order I would expect to see:

On init:

1. Create & bind a VAO. Any VBO and IBO that you bind in the sequence will be associated with the current VAO (this one).

2. Create & bind index buffer.

   • Fill index buffer with glBufferData/glMapBuffer.

3. Create & bind vertex buffer.

   • Fill vertex buffer glBufferData/glMapBuffer.

4. Set up vertex attributes with glEnableVertexAttribArray/glVertexAttribPointer, etc.

5. Optionally unbind everything to avoid accidental modification of the buffers and VAO. Remember to unbind the VAO first. E.g.: glBindVertexArray(0);

On draw:

1. If only drawing the buffers:

   • Bind the VAO;
   • Perform the draw call(s).

2. If updating and drawing:

   • Bind the VAO, VBO, IBO;
   • Update the buffers (updating vertex atributes is only necessary if the vertex format has changed);
   • Perform the draw call(s).

3. Optionally unbind to avoid accidental modification of the buffers and VAO.

That's as simple as that. This order of operations should function without problems.