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

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User:Callahanp/Flightgear and Simgear Code/From Command Line to Holding Short (view source)

Revision as of 02:40, 18 February 2018

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This page covers initialization in flightgear, from the command line through the Splash Page to the first frame of the aircraft in position.


I start by stepping through bootstrap and other modules until flightgear is up and running.
I started by stepping through bootstrap and other modules until flightgear is up and running.
I'm making some notes.  There are three tables below:
I'm made some notes, organized by source code file and function.  The result is the information below.
 
* '''Path''' will trace the path through modules that provide significant functionality to the Simulator until the aircraft is shown holding short or parked somewhere. only the module's source path and a brief explanation or list of why it's on the "path".
* '''Modules''' lists all the classes and methods or functions executed on the "path" as well as those that are not executed in the path.
* '''Utility Calls''' will contain notes on various library calls, noting what the call looks like, where the library comes from, what the call does and where else it might be used. These will be functions with a purpose that is not limited to flight simulation.


====From Command Line to Holding Short====
====From Command Line to Holding Short====
{{See also|Talk:Initializing_Nasal_early#Existing_Initialization_Scheme}}
{{See also|Talk:Initializing_Nasal_early#Existing_Initialization_Scheme}}
When you start flight gear, several activities take place
When you start flight gear, several activities take place


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  * an event loop is started to finish the initialization, display a splash screen.  The event loop then shows the first frame and then adjust the view as time goes on, based on changes in controls, weather, aircraft position, speed, attitude and time.
  * an event loop is started to finish the initialization, display a splash screen.  The event loop then shows the first frame and then adjust the view as time goes on, based on changes in controls, weather, aircraft position, speed, attitude and time.


That's a lot, but the orchestration of all this activity takes place in just a few code files and functions in those files.
* '''Overview''' will trace functions  that provide significant functionality to the Simulator until the aircraft is shown holding short or parked somewhere. only the module's source file-path and a brief explanation or list of the functions used in the "path".
===Overview===
Just to get oriented a little, I'm going to list the top-level routines in the path to holding short.  Initialization happens in four stages, Some stages have very little in them, others have multiple phases and many subsystems to initialize.
{| class="wikitable"
|-
! Startup Stage !! Module !! Routine Signature !! Brief Description
|-
|  1. || Main/bootstrap.cxx || int main(int argc, int char **argv )
|
main contains the initial entry point and final exit.  It initializes things that have to be done early on and decides if we're starting the full application or just a viewer, then calls fgviewerMain(argc, argv) or fgMainInit(argc, argv).  We'll skip the viewer and focus on fgMainInit. 
the main function ias the first of four stages of initialization in Flightgear.  The first stage ends when main calls fgMainInit(argc, argv)
|-
| 2. || Main/main.cxx || int fgMainInit( int argc, char **argv )
|
fgMainInit continues with about 20 individual initializations.
fgMainInit is only the second stage of initialization. It ends with an open but blank window, and a call to fgOSMainLoop();
|-
| 3. || Viewer/fg_os_osgviewer.cxx || int fgOSMainLoop()
|
fgOSMainLoop doesn't do initializations itself.  In fact it is still around for the full duration of the flightgear session.  After marshalling initializations, including those for subsystems, it calls the fgMainLoop.  fgMain lowhere  is responsible for the third stage of initialization.  While its doing initializations it displays the splash screen and messages. Once that's done, it continues sd a driver for everything that happens afterwards. It's amazingly brief, Just four C++ statements on 12 lines of code.
During Initialization Stage 3, fgOSMainLoop calls a routine to do initializations through a pointer, *idleFunc.  During Stage 3, *idleFunc points to fgIdleFunction.
Initializations are done by repeatedly calling fgIdleFunction through the *idleFunc pointer. 
|-
| 3. || Main/main.cxx || static void fgIdleFunction ( void )
|
fgIdleFunction handles all the third stage initializations in a number of phases. It's main work is the initialization of subsystems. It's called many times, and each phase may do one or many initializations.  There are quite a few and it takes a while.  When fgIdleFunction reaches its last initialization state, it calls registerMainLoop() to change *idleFunction to point to fgMainLoop.  Once fgIdleFunction has completed its work it is not run again unless you do a reset, but the routine that called it, fgOSMainLoop continues to run.
|-
| 4. || main/main.cxx || fgMainLoop
| fgMainLoop does not contain a loop, its running under the loop in fgOSMainLoop and will continue to run in that loop until you reset or exit flightgear.  fgMainLoop handles the fourth and final stage of initialization, waiting on the loading of scenery, the airport and the aircraft data.  All the work is handled by subsystems loaded in earlier stages.  The subsystems continue to run after all that's done, and we find ourselves in position at the airport and ready to fly. 
|}
After initialization all of the subsystems needed to fly will be invoked as needed by fgMainLoop, run repeatedly in the actual loop in fgOSMainLoop.
Question:
What in the code finally recognizes that we're ready to display the scene in stage 4?
Are the final initializations done by subsystems done in any particular order?
|-
|
{| class="wikitable"
{| class="wikitable"
|-
|-
! Module
! Module
! colspan="3" | Description & Steps
! colspan="3" || Description & Steps
|-
|-
| src/Main/bootstrap Main  
| src/Main/bootstrap Main  
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