Swap chain: Difference between revisions

Revision as of 22:29, 21 July 2014

Revision as of 01:03, 16 May 2015

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===Direct3D===

[[Microsoft]] [[Direct3D]] implements a SwapChain class. Each host device has at least one swap chain assigned to it, and others may be created by the client application.<ref name="msnd 0">

{{Citecite web

| title = SwapChain Class

| publisher = Microsoft

Line 19:

| accessdate = 30 October 2009

}}</ref> The API provides three methods of swapping: copy, discard, and flip. When the SwapChain is set to flip, the screenbuffer is copied onto the last backbuffer, then all the existing backbuffers are copied forward in the chain. When copy is set, each backbuffer is copied forward, but the screenbuffer is not wrapped to the last buffer, leaving it unchanged. Flip does not work when there is only one backbuffer, as the screenbuffer is copied over the only backbuffer before it can be presented. In discard mode, the driver selects the best method.<ref name="nexe 0">

{{Citecite web

| title = Swap Chains

| publisher = neXe

| url = http://nexe.gamedev.net/directKnowledge/default.asp?p=Swap%20Chains

| accessdate = 30 October 2009

| accessdate = 2015-05-16

}}</ref>

===Comparison with Triple Buffering===

Outside the context of Direct3D, [[Multiple buffering#Triple buffering|triple buffering]] refers to the technique of allowing an application to draw to whichever back buffer was least recently updated. This allows the application to always proceed with rendering, regardless of the pace at which frames are being drawn by the application or the pace at which frames are being sent to the display. Triple Buffering may result in a frame being discarded without being displayed if two or more newer frames are completely rendered in the time it takes for one frame to be sent to the display. By contrast, Direct3D swap chains are a strict [[Queue (abstract data type)|first-in, first-out queue]], so every frame that is drawn by the application will be displayed even if newer frames are available. Direct3D does not implement a most-recent buffer swapping strategy, and Microsoft's documentation calls a Direct3D swap chain of three buffers "triple buffering". Triple Buffering as described above is superior for interactive purposes such as gaming, but Direct3D swap chains of more than three buffers can be better for tasks such as presenting frames of a video where the time taken to [[Data Compression#Video|decode]] each frame may be highly variable. <ref name="anandtech 0">

{{Citecite web

| title = Triple Buffering: Why We Love It

| publisher = AnandTech