Editing Multiple buffering (section)

== Double buffering in computer graphics{{anchor|Double_Graphics}} ==
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In [[computer graphics]], '''double buffering''' is a technique for drawing graphics that shows less stutter, [[screen tearing|tearing]], and other artifacts.

It is difficult for a program to draw a display so that pixels do not change more than once. For instance, when updating a page of text, it is much easier to clear the entire page and then draw the letters than to somehow erase only the pixels that are used in old letters but not in new ones. However, this intermediate image is seen by the user as [[Flicker (screen)|flickering]]. In addition, [[computer monitor]]s constantly redraw the visible video page (traditionally at around 60 times a second), so even a perfect update may be visible momentarily as a horizontal divider between the "new" image and the un-redrawn "old" image, known as [[Page tearing|tearing]].

=== Software double buffering ===
A software implementation of double buffering has all drawing operations store their results in some region of system [[Random Access Memory|RAM]]; any such region is often called a "back buffer". When all drawing operations are considered complete, the whole region (or only the changed portion) is copied into the [[video RAM]] (the "front buffer"); this copying is usually synchronized with the monitor's [[raster graphics|raster]] beam in order to avoid tearing. Software implementations of double buffering necessarily require more memory and CPU time than single buffering because of the system memory allocated for the back buffer, the time for the copy operation, and the time waiting for synchronization.

[[Compositing window manager]]s often combine the "copying" operation with "[[compositing]]" used to position windows, transform them with scale or warping effects, and make portions transparent. Thus, the "front buffer" may contain only the composite image seen on the screen, while there is a different "back buffer" for every window containing the non-composited image of the entire window contents.

=== Page flipping ===
In the page-flip method, instead of copying the data, both buffers are capable of being displayed. At any one time, one buffer is actively being displayed by the monitor, while the other, background buffer is being drawn. When the background buffer is complete, the roles of the two are switched. The page-flip is typically accomplished by modifying a [[hardware register]] in the [[video display controller]]—the value of a pointer to the beginning of the display data in the video memory.

The page-flip is much faster than copying the data and can guarantee that tearing will not be seen as long as the pages are switched over during the monitor's [[vertical blanking interval]]—the blank period when no video data is being drawn. The currently active and visible buffer is called the '''front buffer''', while the background page is called the '''back buffer'''.