Page tearing

Screen tearing is a visual artifact in video display where a display device shows information from multiple frames in a single screen draw.

The artifact occurs when the video feed to the device is not in sync with the display's refresh rate. This can be due to non-matching refresh rates—in which case the tear line moves as the phase difference changes (with speed proportional to difference of frame rates). It can also occur simply from lack of sync between two equal frame rates, in which case the tear line is at a fixed location that corresponds to the phase difference. During video motion, screen tearing creates a torn look as edges of objects (such as a wall or a tree) fail to line up.

Tearing can occur with most common display technologies and video cards, and is most noticeable in horizontally-moving visuals, such as in slow camera pans in a movie, or classic side-scrolling video games.

Screen tearing is less noticeable when more than two frames finish rendering during the same refresh interval, since this means the screen has several narrower tears instead of a single wider one.

Ways to prevent video tearing depend on the display device and video card technology, software in use, and the nature of the video material. The most common solution is to use multiple buffering.

Most systems use multiple buffering and some means of synchronization of display and video memory refresh cycles.

Vertical synchronization is an option in most systems, wherein the video card is prevented from doing anything visible to the display memory until after the monitor finishes its current refresh cycle.

During the vertical blanking interval, the driver orders the video card to either rapidly copy the off-screen graphics area into the active display area (double buffering), or treat both memory areas as displayable, and simply switch back and forth between them (page flipping).

Nvidia and AMD video adapters provide an 'Adaptive Vsync' option. This will only turn on vertical synchronization when the frame rate of the software exceeds the display's refresh rate, disabling it otherwise. This eliminates the stutter that occurs as the rendering engine frame rate drops below the display's refresh rate.

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