Appendix M. Flipping and UBB
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## Appendix M. Flipping and UBB

The NVIDIA Accelerated FreeBSD Driver Set supports Unified Back Buffer (UBB) and OpenGL Flipping. These features can provide performance gains in certain situations.

- Unified Back Buffer (UBB): UBB is available only on the Quadro family of GPUs (Quadro4 NVS excluded) and is enabled by default when there is sufficient video memory available. This can be disabled with the UBB X config option described in Appendix D, X Config Options. When UBB is enabled, all windows share the same back, stencil and depth buffers. When there are many windows, the back, stencil and depth usage will never exceed the size of that used by a full screen window. However, even for a single small window, the back, stencil, and depth video memory usage is that of a full screen window. In that case video memory may be used less efficiently than in the non-UBB case.

- Flipping: When OpenGL flipping is enabled, OpenGL can perform buffer swaps by changing which buffer the DAC scans out rather than copying the back buffer contents to the front buffer; this is generally a much higher performance mechanism and allows tearless swapping during the vertical retrace (when __GL_SYNC_TO_VBLANK is set). The conditions under which OpenGL can flip are slightly complicated, but in general: on GeForce or newer hardware, OpenGL can flip when a single full screen unobscured OpenGL application is running, and __GL_SYNC_TO_VBLANK is enabled. Additionally, OpenGL can flip on Quadro hardware even when an OpenGL window is partially obscured or not full screen or __GL_SYNC_TO_VBLANK is not enabled.

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