Two Rendering Modes
The presence of scene-graph support classes underscore that M3G supports "immediate" and "retained" rendering modes. In immediate mode, objects are rendered at once, applying the lighting conditions from an array of current Lights and a current Camera that determines the final image's POV. Objects rendered in immediate mode can be portions of a scene graph or individual meshes. Immediate mode offers low-level control of the rendering operations.
In retained mode, rendering operations are managed at a higher level. Each model's geometric data and appearance attributes are encapsulated in instances of scene-graph objects stored within a scene graph. A scene graph consists of a tree structure of data that describes all of the objects in a 3D world, along with its Lights and Cameras. These classes contain visibility flags and instances of them can be made visible or invisible under program control. In retained mode, scenes aren't rendered all at once. Instead, the rendering engine traverses the scene-graph tree, using the visibility flags, object positions, and POV to cull surfaces before rendering final images. This lets the rendering operation be optimized for performance. Only one Camera can be active at a time. Choosing a different Camera and making it the active one lets you immediately change the scene's POV.
Because the immediate-mode operation allows access to low-level primitives, you can define a model's surfaces through the use of algorithms or VertexArrays. However, for complex models it's easier and less memory-intensive to have Loader read the model from a scene graph stored in an M3G file.