• Overall Structure
• Rendering Rules

Overall Structure

The PIGGE system consists of several main modules which control the overall program flow; several specialized modules that encapsulate various functional areas, such as physics models and particle effects; and a set of driver modules that handle low-level functions, including event handling, 3D rendering, and so on.

No modules outside of the drivers should contain any non-portable code; all API-specific functionality should appear only in the drivers. While the default supported APIs are fairly generic and portable (SDL, OpenGL, and so on), there will doubtless be environments that do not support them or have more colloquial local APIs. This separation will aid a porting effort for these platforms, and at the same time keeps a nice clean conceptual wall between design and implementation in the engine.

Rendering Rules

In order to maintain consistency (and sanity), functions in the rendering drivers must follow the following rules:

• Functions that affect the viewport and projection must do only those things, and no other functions may do so. Furthermore, these functions must return to the modelview matrix mode before returning, and generally should load an identity modelview at the same time.
• Functions must leave the various matrices unchanged when they return, unless their main function is to change state.
• Designs must optimize for doing as much as possible in the hardware, and with as few round trips as possible. The engine should even run fairly efficiently with the rendering hardware on a different system, across the network from the CPU!