Graphics.GL.Low.VAO

Documentation

Vertex Array Objects (VAO). Despite having almost no operations of its own, the VAO mechanism is one of the most complex pieces of OpenGL. A VAO has mutable state which associates vertex shader input variables (actually the integer location of the variable) with three things:

• The VBO to read from.
• The position in the each vertex array (in the VBO) to read from.
• The interpretation of the bytes found there (32-bit float, 16-bit int, etc).

You set these VAO parameters with the following dance:

• Bind a VAO
• Bind a VBO
• Use a Program
• call setVertexLayout which will lookup the position of the input variables and issue the appropriate glVertexAttribPointer calls.

After a VAO is configured against a Program, either can be swapped in or out freely and they will still work when both are swapped in again together.

An "in-use" program will use whatever VAO is bound for getting its vertex inputs. It is up to the programmer to ensure that the VAO has been configured with the right variable positions for the current program. Two ways to do this are to use a consistent set of variables for all shaders or restrict a set of VAOs to only be allowed with specific Program objects.

The currently bound VBO is not remembered or restored by binding a VAO, but the currently bound ElementArray is. This detail won't affect you if you always explicitly bind an ElementArray after binding a VAO. Alternatively you can exploit this to bundle particular models and their element arrays as a VAO.

Diagram of possible VAO contents:

The above VAO would be compatible with the following vertex program:

#version 150

in vec2 position;
in vec3 color;

out vec3 Color;

void main()
{
    gl_Position = vec4(position, 0.0, 1.0);
    Color = color;
}

newVAO :: IO VAO

Create a new VAO. The only thing you can do with a VAO is bind it to the vertex array binding target.

deleteVAO :: VAO -> IO ()

Delete a VAO.

bindVAO :: VAO -> IO ()

Assign the VAO to the vertex array binding target. The VAO already bound will be replaced, if any.

data VAO

Handle to a VAO.

Instances

Show VAO

GLObject VAO