Game loop

A place for users of OGRE to discuss ideas and experiences of utilitising OGRE in their games / demos / applications.
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Ephon
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Game loop

Post by Ephon » Fri Jan 28, 2005 12:37 am

Just wonderering:

Does the order in which things get done matter when it comes to the game loop?

Take for instance:

Code: Select all

while(!shutdown)
{
    DoInput()
    DoGameLogic()
    DoRender()
}
versus

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while(!shutdown)
{
    DoRender()
    DoGameLogic()
    DoInput()
}
Does it matter that rendering comes before inputhandling?

And must the framelistener notification(framestarted/frameended) be like this:

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while(!shutdown)
{
    Root::_frameStarted()
    DoRender()
    DoGameLogic()
    DoInput()
    Root::_frameEnded()
}
or is it just as good to put the framelistener notification inside DoRender():

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DoRender()
{
    Root::renderOneFrame()
}
All this is with regard to timing issues and game experience etc.
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Emmeran
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Post by Emmeran » Fri Jan 28, 2005 2:18 pm

ok... let's see...

as long as u don't use global variables u changed in one of the other functions u should be able to order the functions as u like.

the frameStarted() event will be fired automatically by Root::renderOneFrame()

--
i don't know if u knew but u can create an instance of framelistener like this:

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class someClass : public Ogre::FrameListener
{
     bool frameStarted(FrameEvent &evt);
     bool frameEnded(FrameEvent &evt);
};

bool someClass::frameStarted(FrameEvent &evt)
{
     //do what u like to be done before rendering
     return true;
}

bool someClass::frameEnded(FrameEvent &evt)
{
     //do what u like to be done after rendering
     return true;
}
edit:
the function frameStarted and frameEnded will be called automatically, if u have registered the framelistener with Ogre. I think u have to do something like this:

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myPointerToSomeClass = new someClass();
Root::registerFrameListener(myPointerToSomeClass);
look in the api if i'm wrong

good luck,
Emmeran
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jacmoe
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Post by jacmoe » Fri Jan 28, 2005 11:25 pm

Generally, you don't have to worry about Ogre doing it's magic - after Root::startRendering() it happens automatically.
For your own stuff, you can use framelisteners to execute code on a frame by frame basis.
That can be input, AI, etc.

Forget about renderOneFrame(), etc. The only time when you want to update the renderloop manually, is when writing gui tools (MFC for instance).

Feel free to search around for more on this subject - there's a lot on that in the Ogre fora. :)
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Kobold
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Post by alphabeta » Sat Jan 29, 2005 4:17 am

[quote="jacmoe"]Forget about renderOneFrame(), etc. The only time when you want to update the renderloop manually, is when writing gui tools (MFC for instance).quote]

That's not entirely true, if you're writing a framework independant of Ogre you'll need to use renderOneFrame() in your own loop
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Kristian
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Post by Kristian » Sat Jan 29, 2005 9:59 pm

I take it that you dont want to use the Ogre::Root::startRendering and Ogre::Framelistener's and manually make your own game loop ?!?
In that case it would be most correct to render something after you've done your logic and simulating of the world it would be more natural to render what you have in the current step/"world state" and not the previous step. So yes this means that you will have a loop that loops somethink like this:

void loop () {

while(1) {
handleInput();
doGameLogic();
doRenderWorld();
}
}
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tuan kuranes
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Post by tuan kuranes » Sat Jan 29, 2005 10:13 pm

Here's an interesting thread about this :
http://groups-beta.google.com/group/com ... b5a4bb9589
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