I to handle my game at an interval of 60 fps, but let it draw in
sync with the display's refresh rate.
I used AGL_SWAP_INTERVAL for a long while.
If I handle the game at 60 fps and the monitor refresh rate is
60Hz, everything is fine.
The problem is, if I want to handle the game at 60 fps and the
monitor refresh rate is 75Hz, the animation is no longer very smooth.
Going into full screen mode and setting the refresh rate to 60Hz
doesn't work on all displays. Also, it is a very common feature
these days run the game in window mode.
The question is, how can I let be game be handled at 60 fps, while
drawing at whatever the monitor's refresh rate is, without
impacting performance of the game (assuming the hardware can keep up.)
I have put together a small demo. http://www.foxchange.com/matt/temp/refreshSyncProblem.sit
In your demo you have an EventLoopTimer to call your game
calculations at regular intervals --- of order 1/60s --- and a second
timer that calls aglSwapBuffers() at regular intervals, also of order
1/60s. That approach won't properly synchronize (or more accurately,
serialize) the successive phases of the game cycle.
I suggest that you write a central function like OneCycleOfMyGame
below, and call it from a single EventLoop timer. The pseudo C code
assumes one common way to represent a moving object or sprite, namely
a struct that specifies position, velocity and no doubt additional
variables. Position is updated every frame, using the velocity as
determined by your UI, gravity, collisions and so on. Position and
velocity have x and y components (and z, for 3D).
/* Game calculations */
for ( each sprite )
{
sprite->velocity = MySpriteVelocityCalc( sprite );
sprite->position += sprite->velocity * deltaT;
}
/* Draw a frame */
MyOpenGLStartDrawingFrame(...);
for ( each sprite )
{
MyOpenGLDrawSpriteFunction( sprite );
}
MyOpenGLFinishDrawingFrame(...);
/* Show the frame */
aglSwapBuffers( gMyOpenGLContext );
}
int main( void )
{
MyInitializeGame();
// Set up an EventLoopTimer to call OneCycleOfMyGame
// every 1 ms (the real interval will be much longer).
MyInstallTimer( kEventDurationMillisecond, OneCycleOfMyGame );
RunApplicationEventLoop();
return 0;
}
OneCycleOfMyGame() ensures that everything is done at the right time
and in the right order. Moreover, it automatically makes the speed of
sprite movement independent of frame rate (which is why you use the
sprite's velocity and deltaT in calculating the new position). To a
first approximation, you don't need to worry about the actual frame
rate, as long as it's not so low as to make the movement jerky or so
high as to heat up the processor unnecessarily.
Robert P.
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