What tearing looks like
Sometimes during fast movement a game picture appears to be sliced into two or more horizontal bands, with the bands slightly out of line with each other. A vertical edge, such as a doorframe, may look broken where the slices meet. This is screen tearing.
It is not a fault in the display or a damaged cable. It happens when the screen starts showing a new picture before it has finished showing the previous one, so you see parts of two different frames at once.
Why it happens
Two separate clocks are at work. The game finishes new frames whenever the graphics card has completed them, and this timing varies from moment to moment. The display, meanwhile, redraws itself at a regular rhythm set by its refresh rate. A typical screen does not update every pixel at the same instant; it sweeps down the panel from top to bottom, line by line, many times per second.
The graphics card normally keeps the finished frame in a memory area that the display reads from. If a new frame replaces it while the display is partway down the screen, the lines above that point come from the old frame and the lines below come from the new one. The boundary between them is the tear.
Several things make tearing more visible:
- Fast sideways motion, where the difference between consecutive frames is large.
- A frame rate that is not matched to the refresh rate, particularly one that fluctuates.
- A frame rate above the refresh rate, which produces more chances for a swap in the middle of a redraw.
Tearing can happen at low frame rates as well, so it is not simply a sign that the game is running too fast.
How V-Sync works
V-Sync, short for vertical synchronization, tells the graphics card to wait. Rather than swapping in a new frame at any moment, it holds the swap until the display finishes its current redraw and is about to begin the next one. That brief gap between redraws is known as the vertical blanking interval. Because the swap happens only then, each redraw contains one complete frame, and tearing disappears.
For many players, that is exactly what they want. The picture is clean, and the game does not push out frames the display cannot show anyway.
The cost of waiting
Waiting has side effects, which is why V-Sync is not simply switched on for everyone.
Added delay. A finished frame may sit for a short time until the next redraw begins. In many setups, the game also queues a few frames ahead. The combination can make controls feel slightly less immediate. Players who are sensitive to input latency, such as those in fast competitive games, often notice this more than others.
Uneven pacing when the game cannot keep up. If the game cannot finish a frame in time for a redraw, the display repeats the old frame and waits for the next opportunity. On a fixed refresh rate, that means the effective frame rate can drop in steps rather than gradually. A game that would otherwise run a little below the display’s rate may fall to a fraction of it, such as half. The result can feel more like stutter than the tearing you were trying to avoid.
The extent of these effects varies by game, driver and display, so it is better to test than to assume.
Buffering variations
Some systems use more than two frame buffers so the graphics card can keep working while a finished frame waits. This is sometimes called triple buffering. It can reduce the step-down effect described above, because the card does not have to idle while waiting for a redraw. The trade-off is typically an extra frame of delay and a bit more memory use. Names and behavior differ between games and platforms, so treat the label as a hint and check what the setting actually does in your game.
Some games and drivers also offer a “fast” synchronization mode that keeps the game running freely and sends only the newest completed frame to the display at each redraw. It avoids tearing and keeps delay lower than classic V-Sync, but it generally needs the game to run well above the refresh rate to be worthwhile, and it can look slightly uneven.
Adaptive and variable refresh
A different solution is to let the display follow the game instead of the other way around. Variable refresh rate screens can start a redraw when a new frame is ready, within a supported range. Because the display waits for the frame, there is no mid-redraw swap, so no tearing, and no fixed schedule to miss, so less of the stepping effect. Marketing names for this vary between vendors and standards, but the principle is the same.
Variable refresh needs a compatible display, a compatible graphics card and a cable and settings that support it. It also works only within a certain range, and outside that range the display falls back to ordinary behavior. Some players pair it with a frame rate cap just below the display’s maximum so that the game stays inside the range. It does not remove other sources of uneven motion, such as the game itself hitching.
Choosing what to do
A practical way to think about it:
- Is tearing bothering you? If not, leaving sync off may give you the lowest delay.
- Is your frame rate usually close to or above your refresh rate? Classic V-Sync tends to work best here.
- Is your frame rate unsteady? A variable refresh display, if you have one, usually handles this best.
- Do you care most about the quickest response? You may accept some tearing, or use a limiter and a fast mode, in exchange for lower delay.
Because outcomes depend on the combination of game, hardware and settings, small experiments are worth more than rules of thumb. Change one setting at a time and judge both how the picture looks and how the controls feel.
Related ideas
Tearing sits alongside several other ideas that are explained elsewhere. The refresh rate of the screen and the frame rate of the game are separate quantities. Network trouble such as ping time is unrelated to tearing, even though both can be described loosely as “lag”. And while tearing is a display synchronization issue, the different delays that make a game feel unresponsive come from other places.