A scene graph is a data structure commonly used to construct hierarchical representations of spatial graphical scenes. The main limitation of the classes introduced in Chapter 6, OpenGL ES 3.1 and Cross-platform Rendering is that they lack information on the scene as a whole. Users of these classes have to do ad hoc bookkeeping of transformations, state changes and dependencies, making implementation and support of any somewhat complex scenes a very challenging task. Furthermore, a lot of rendering optimizations cannot be done unless the whole scene information for the current frame is accessible.

In our current low-level implementation, we describe all visible entities using the clVertexArray class and render them using a shader program accessible via the clGLSLShaderProgram class with an ugly manual binding of matrices and shader parameters. Let's learn how to put all these properties together into a higher level data structure. First, we will start with a scene graph node...