The actual frame rate in games
We are all accustomed to measuring smoothness in games (both computer and mobile) with a frame rate of a second. And, it seems, it looks right. But is it really? And in general, what is FPS? How is it calculated? And if it is not enough for a correct understanding of smoothness in games, what else is needed? We will talk about all this.
FPS
What is FPS?
Stands for Frames per second, which literally translates frames per second. This parameter indicates the number of exchangeable frames per unit time, in this case in the second. As you know, the more of them, the smoother the picture looks like, because the movement of objects on it there is a "slower", which simplifies the gameplay, or make it more comfortable, due to lower requirements for our speed of reaction to what is happening on the screen. It seems simple, yet why some parameters? The fact is, like the FPS is calculated, or rather where and which way he goes up to the user, because the footage depicts the GPU, rather than the screen.
Calculate the number of FPS and their path to the screen
As I said above, frame rendering (FPS) occurs in the GPU (when working with software game engine), and that is where it is calculated by different programs like Fraps on a PC or Gamebench mobile devices. The problem is that there is a problem frames, so-called "short", or incomplete frames and discarded frames. The first is so small and not durable (their "length" of 20 pixels or less), the duration (a couple of tens of milliseconds) of their location on the screen simply invisible to the human eye, although they stop frame are clearly visible. The usefulness of such personnel for the gamer is zero, but they are still there. This is called microshuttering. And just including them, Fraps and Gamebench figure is calculated FPS. By itself this figure is useless. The PC-game cobschestve it is called "corn" FPS. But then the question arises, where the lost are frames that do not reach the screen, and as they appear?
Here is a diagram of the path of the game scene (frame) to the gamer -
(change MS DX to OpenGL ES)
At the stage of present (currently) measured by FPS. But the screen of the smartphone even as much as 4 steps. It is logical that not all frames can walk from the GPU to the screen. They may lose both because of the graphics library, and because of the drivers. That this response. Because of human imperfection (and often just lazy :), or lack of motivation), these two things are not ideal. Consequently, not all frames are considered Fraps and the FPS, really benefit and make the game smoother picture. So, in some cases, from them may be of little use. The appearance of such frames, see the link below in the spoiler FAQ. How to solve this problem? Indeed, in view of this situation, producers or GPU developers can easily deceive us, even without any synthetics. Even the number of frames, it is not an authority.
We need some way to see the uniformity of the frame for all the steps, from the game engine, up to the screen. Simple programs can not do. On a PC, this problem was solved by hardware-software complex FCAT, which is released in the spring of 2013 Nvidia. Several laboratories have them (overclockers.ru, iXBT.com, THG.ru). But how to solve this problem in our segment, the segment of mobile gaming? The only way to solve the problem would be similar complex, which will also determine the uniformity of the frame, with the video output. This can be realized if the output image wired manner on an external screen over HDMI, MHL, or any SlimPort. While this problem is not solved, and we only need to wait for its solution. Thank you all for your attention.
The effect of memory bandwidth on the performance of a GPU -
video memory bandwidth