When rendering graphics or video to the screen, it’s important to understand the display process; in particular, vertical sync (v-sync). A common problem when starting out is an issue called “tearing”… where the video appears to be torn horizontally down the middle (see picture). I’ve been looking for a good explanation to share about why video tearing occurs and how to solve it (from a technical perspective). I found the following thread over at [H]ard|Forum, which I think does a pretty good job.
For the thread “How VSync works, and why people loathe it“:
There is a technique called triple-buffering that solves this VSync problem. Lets go back to our 50FPS, 75Hz example. Frame 1 is in the frame buffer, and 2/3 of frame 2 are drawn in the back buffer. The refresh happens and frame 1 is grabbed for the first time. The last third of frame 2 are drawn in the back buffer, and the first third of frame 3 is drawn in the second back buffer (hence the term triple-buffering). The refresh happens, frame 1 is grabbed for the second time, and frame 2 is copied into the frame buffer and the first part of frame 3 into the back buffer. The last 2/3 of frame 3 are drawn in the back buffer, the refresh happens, frame 2 is grabbed for the first time, and frame 3 is copied to the frame buffer. The process starts over. This time we still got 2 frames, but in only 3 refresh cycles. That’s 2/3 of the refresh rate, which is 50FPS, exactly what we would have gotten without it. Triple-buffering essentially gives the video card someplace to keep doing work while it waits to transfer the back buffer to the frame buffer, so it doesn’t have to waste time. Unfortunately, triple-buffering isn’t available in every game, and in fact it isn’t too common. It also can cost a little performance to utilize, as it requires extra VRAM for the buffers, and time spent copying all of them around. However, triplebuffered VSync really is the key to the best experience as you eliminate tearing without the downsides of normal VSync (unless you consider the fact that your FPS is capped a downside… which is silly because you can’t see an FPS higher than your refresh anyway).
If the thread is ever unavailable, you can download a PDF version HERE.
