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Code entry point

Posted by Norman Barrows, 06 September 2013 · 446 views

Code entry point



ok here we go....


<Code entry point>
init_program
run_program
end_program
<halt>



that's a game, right there. this is what all games do. actually is what pretty much all programs do.
<Code entry point> is where program execution begins, main() for example in C++.
<halt> is where the program ends execution.

init_program:
this is where you display your title screen, and show any opening animation, and initialize all program level variables.and data structures. create a window, start your graphics and sound libraries, load assets (graphics and audio data files), etc.



As i provide code examples, i intend to also discuss topics related to the code.

init_program brings up the first topic:

loading of assets.
making the user wait while loading assets is bad. its usually easiest to load all assets at program start if possible. or at level start if necessary. or page assets if needed. or background stream. the slick implementation does a foreground load of enough content to
get things started while it streams the rest in the background for the remainder of the game. A single wait for asset load at program start is usually considered preferable to one per level, etc.


In a typical title, in init_program, i'll create a window, start up directx, and load meshes, textures, materials, models, animations, and audio.

end_program:
release assets, shutdown graphics and audio.
not much to it. just RTFM for your libraries, and do what it says.

run program:
this is the main menu, or wrapper menu system, or "shell" for the game. Not all games have a start-up menu, but most do. For a game with no start-up menu, this would immediately run the game. A typical start-up menu will have options for starting a new game, loading a saved game, setting game options, help, and quit.

new game:
initgame
rungame
endgame

load game:
initgame
loadgame
rungame
endgame

both menu options are almost the same. note that in load game, initgame is called, despite the fact that a game is being loaded. there's a reason for this. its possible to design save game file formats that automatically convert older formats to new formats. for this to work, variables not contained in the older format must be initialized. the easy way to do this is to use initgame to initialize everything, then use loadgame to overwrite just the data contained in the save file. this lets you load an old format game, and initializes the new variables with default values. when you save, its saved in the new format, which includes the new variables.



init game:
here you initialize any game level variables and data structures. exactly what depends on whether the game is mission based or not.

run game:
for a non mission based game, this is the main loop. for a mission based game, this runs the "between missions menu", which in turn calls initmission - run mission - end mission, where runmission is the main game loop.

end game:
anything that happens at the end of a single game goes here, such as a high scores display.


rungame for a mission based game:
this will have the "between missions menu". selecting "next mission" starts the next mission.

next mission:
init_mission
run_mission
end_mission

init_mission:
load the level, init all targets, etc.

end_mission:
mission debriefing

run_mission:
the main game loop



up next: main game loops




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