User:Callahanp/Flightgear and Simgear Code/From Command Line to Holding Short: Difference between revisions

This page covers initialization in flightgear, from the command line through the Splash Page to the first frame of the aircraft in position.  This page is intended to be read with flightgear and simgear open in an editor, preferably one with a global search capability.  In addition you may want to step through some parts of the flightgear code in a debugger capable of setting break points. I'll assume you don't need advice on which editor and debugging tools to choose or how to set them up.

Flightgear consists of a number of subsystems, responsible for various aspects of the illusion of flight.  When the command to start flightgear is given, the environment capable of supporting the display of aircraft and scenery is initialized.  By reviewing this initialization process step by step, you gain an overview of the main components of flightgear and insight into areas you may want to similarly explore in detail.

We'll start by stepping through bootstrap and other modules until flightgear is up and running and the aircraft is visible, holding short, in a parking area, or placed on a runway waiting for takeoff clearance.  I'll provide explanations where I think they're needed, but mostly you will just be looking at specific parts of specific modules and drawing your own conclusions and making notes.  While the initialization of sub-systems does provide some insight into the organization of the code, the real functionality of the subsystems is invoked later, during frame by frame display of the simulation.  A second companion wiki page goes into additional detail on each subsystem. A third wiki page details the cycle of execution for each frame.

There is ongoing work by Edward d'Auvergne in the area of initialization. Where appropriate, I'll refer to various things Edward has noted in e-mails to the flightgear-devel mailing list.

We'll trace our way through the code and highlight specific lines of code that make up this process.  We'll cover both the initial startup and the differences in the initialization process when resetting the application.