Game loop alternatives for efficiency

Question

Understand where I'm coming from - I've been taught that a game is implemented something like this (pseudocode):

while (!win_condition)
{
   waitforinput();
   updategraphics();
   //etc..
}
exit();

Is there another way to implement the "game loop" without limiting the game to finite "turns"?

This

while (true) 

business seems to eat a lot of CPU, especially for how simple a game I'm making!

Answer 1

If your game loop is not throttled to a given framerate it will run as fast as it can. Do a google search for fixed time game loop and you'll find in depth comparisons on how these work.

Basically you measure how long your loop iteration took to complete compared to how much time you have per frame at your given frame rate (e.g. at 25fps you'll have 1/25th of a second to complete your game loop while maintaining your frame rate) and sleep for the remainder of time.

Another approach that can work if your game is event driven and has static graphics between events is to poll for user input every so often and then sleep.

Answer 2

That really is the best way. Even with a multi-threaded engine, you want to use task batching, so your main loop will still be "update system A, then system B, etc."

So far as eating up CPU, you definitely want to be conscious of that, especially on mobile gaming (but even for PC gaming due to the rising popularity of mobile PCs).

First, always use sync-to-vblank. That'll keep your game loop from running faster than the display. You can use a custom frame rate controller if vblank syncing is for some reason not usable (or if you are using triple buffering). Basically put a microsecond-accurate sleep (not a busy loop) at the end of your loop after doing the buffer swap in order to keep the game from running faster than you need it to.

You can also replace the part that queries system events (the Win32 message pump, for instance) between blocking and non-blocking when you go into screens that have no animation running when the player isnt doing anything, such as a pause screen or the main menu.

Answer 3

There are ways to handle the loop differently but since you said your game was so simple, the standard loop is probably what you want. Other ways would probably make the code more complex than what I'm guessing you are interested in.

Its true that the while loop has some issues, like how it will run at different speeds depending on the CPU, but its kinda the de facto standard.

That and it's not really the while loop that eats a lot the cpu, it's what you do in the loop that makes the most impact. You are always going to want a loop for any graphical game because there is no easier way to constantly check the exit condition of your game and update graphics, physics, input, etc.

Answer 4

Dosen't matter. The win_condition will be true most of the time. It is the same of putting 'true' directly. And the 'true' approach saves memory, one less variable.