VertexArrayObject support

[axel22]

VAOs are used as a shorthand for setting the state of the vertex processor, and, once the vertex attributes and pointers are set while a VAO is bound, subsequently binding the VAO does not require setting the vertex attribute buffers and pointers.

Right now, in the single triangle example, we access VAOs using the low-level OpenGL API:

https://github.com/storm-enroute/macrogl/blob/master/src/test/scala/org/macrogl/examples/SingleTriangle.scala#L14

We need a better support for VAOs.
We must do the following:

• introduce VertexArrayObject.scala, which extends Handle, and its acquire generates a name, just like Program, Texture, RenderBuffer and others
• introduce object VertexArrayObjectObject { def foreach = ... } in using: https://github.com/storm-enroute/macrogl/blob/master/src/main/scala/org/macrogl/package.scala#L115
• have a foreach and a macro associated, just like with other kinds of using objects - it sets and unsets the VAO
• add a def vertexArrayObject(vao: VertexArrayObject) = VertexArrayObjectObject

This should allow the following syntax:

val vao = new VertexArrayObject
vao.acquire()

// loop

for {
  _ <- using.vertexArrayObject(vao)
  ... all the rest ...
} {
  // rendering
}

// later
vao.release()

Then, I would create a lazy default VAO lying somewhere in package.scala:

Default.VAO

So that the developers can fetch it immediately without creating it:

for {
  _ <- using.vertexArrayObject(Default.VAO)
} {

[axel22]

@storm-enroute-bot

[axel22]

@storm-enroute-bot

[axel22]

@storm-enroute-bot

[axel22]

@storm-enroute-bot