Regarding "One Frame Thread Lag"

[[TW]redeye]

Originally Posted by Proud_God

1) if your game thread is consistently faster than your render thread, won't you be in the same situation with OFTL on as off, with the added downside that you are constantly 1 frame behind?

Think about that again. Hint: The key is to think with parallelism in mind.

Originally Posted by Proud_God

2) I suppose the client side hit detection uses the game thread to determine the game state. But, with OFTL on, won't that mean that it is more difficult to hit people, since you might be looking at a screen that is no longer current with regards to the game thread.
I seem to notice it is harder for me to hit enemies with OFTL on, which supports this.

Refer to my first post on this thread.

[Mike_Nomad]

"A programmer is just a tool which converts caffeine into code"

Man, ain't that the truth.

[Proud_God]

Originally Posted by [TW]redeye

Think about that again. Hint: The key is to think with parallelism in mind.

I understand that OFTL gives more pararellellism as the 'frame queue' (which has a max length of, as I understand it, only 1 frame) is being filled. However, once the frame queue is full, you are stalling for the N+2'th frame to finish.

How is this situation better than being stalled for the N+1'th frame with OFTL off (even more, it is worse as you are one frame behind)

Correct me if I'm wrong ofcourse

I also note that for myself, I gain little to no fps from OFTL, only some input lag.

[[TW]redeye]

Ok, for the sake of argument let's assume that your game thread consistently takes 5ms to run and the render thread takes 10ms to run.

If you run with OFTL off, once the render thread has finished rendering the frame (10ms), it has to wait an additional 5ms for the game thread to finish computing the next frame before it can do any work. Since the render thread is not allowed to lag behind (also read as since the game thread is not allowed to work ahead) there is no queued frame. Hence, the effective time to render a frame from the render thread's perspective becomes 15ms.

On the other hand, if you have OFTL enabled, by the time the render thread has finished rendering one frame, it will already have a queued up frame to work on immediately. So the effective render time is now 10ms as opposed to 15ms.

Of course, if the render thread is more than 2 times slower than the game thread, then it will not always have a queued up frame, and as a result OFTL will yield diminishing returns.

[Proud_God]

Originally Posted by [TW]redeye

If you run with OFTL off, once the render thread has finished rendering the frame (10ms), it has to wait an additional 5ms for the game thread to finish computing the next frame before it can do any work.

The confusion is still not cleared up. In your original post you said, regarding the OFTL off scenario:

"While the Nth frame is being rendered, the game thread can compute your (N+1)th frame in parallel."

This seems in conflict with the quoted sentence above?

[[TW]redeye]

Originally Posted by [TW]redeye

If you run with OFTL off, once the render thread has finished rendering the frame (10ms), it has to wait an additional 5ms for the game thread to finish computing the next frame before it can do any work.

This is for the render thread.

Originally Posted by Proud_God

"While the Nth frame is being rendered, the game thread can compute your (N+1)th frame in parallel."

This is for the game thread.

The game thread is not dependent on the render thread, and hence can start computing the next frame before the render thread has finished. But the render thread is dependent on the game thread, and cannot begin a frame before the game thread has finished.

Also, I was being very simplistic in my 5ms, 10ms example. I hope you get the idea. You'll just have to put 2 and 2 together. Unfortunately, this is about as much detail I can go into in the forums.

[Proud_God]

Sometimes pictures say more than words, so here is my understanding of the scenario where game thread = 5ms and render thread = 10ms.
Beyond the initial throughput increase for the game thread, I see no advantage of OFTL. Where is this interpretation wrong?

Note: I realize this is a simplified scenario, but it gets my point across.
In cases where the render thread is sometimes faster and sometimes slower than the game thread, I can imagine there being more benefit.

[mattlach]

Originally Posted by Proud_God

Sometimes pictures say more than words, so here is my understanding of the scenario where game thread = 5ms and render thread = 10ms.
Beyond the initial throughput increase for the game thread, I see no advantage of OFTL. Where is this interpretation wrong?

Note: I realize this is a simplified scenario, but it gets my point across.
In cases where the render thread is sometimes faster and sometimes slower than the game thread, I can imagine there being more benifit.

I think that is fairly accurate, except for the part where you are assuming that the render pipeline flows at an even rate.

Each frame is different, and as such takes more or less time to finish rendering. Having that n+1 th game thread I think makes more of a difference when things slow down and speed back up again.