Question

My question is about game loop design in opengl.

I believe that game loop can be spited in 3 main steps

1. accept input – it may come from users click on the screen or system alert, or anything else.
2. do logic
3. update view

To make it simple let’s just focus on step 2 and 3.

I think that it will be wrong to run them in parallel order or to mix them in to one step.
I give you an example.

Lats say you are creating a war game, and you need to draw 100 soldiers fighting on the screen, the logic will be to update their position, to update the background area, and then you need to draw the result. You can’t start drawing one soldier before updated the position of another soldier.

So according this simple steps, it is clear that step 2 and 3 need to be synchronized some how, and step 2 must be done before step 3.

Now tell me how it is possible to run game loop on more then one thread, and more then one process? Does opnegl use multiCore? How?

Edit: one way to use multithreading is to precalculate the game logic, or in another words using Vectors. But there are two big disadvantages in vectors that make them almost unrecommend to use.

1. Some times you wan’t to change your vector, so there were lots of calculation that you did and you are not going to use them
2. in most of the cases you are trying to reach 60+ FPS witch mean 16 milliseconds for game-loop, switching threads requires some kind of synchronization, any synchronization is bad for performance, from what I saw, even a simple Handler.post() in android(just adding task to queue to run it on other thread) may take up to 3 milliseconds(18% from your frame rate time), so unless your calculation take longer then that, don’t do it! For now I did not found anything taking so much time.

Answer 1

Now tell me how it is possible to run game loop on more then one thread

The idea of multicore computing is parallelization, i.e. splitting up computational intensive tasks into independent working sets that can be processed in parallel. Games have surprisingly little space for parallelization, as you found out yourself.

The usual way to use multiple cores in games is to parallelize I/O with logic operations. I.e. doing all the networking and user interaction in one thread, AI and scene management in another. Sound is usually parallelized away, too.

Does OpenGL use multiCore? How?

The OpenGL specification doesn’t specify this. But some implementations may choose to utilize multiple cores. though it’s quite unlikely. Why? Because it creates unneccessary cache management overhead.