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40 <h2 class="title"><a name="flippingubb" id=
41 "flippingubb"></a>Chapter 19. Configuring Flipping and
46 <p>The NVIDIA Accelerated FreeBSD Graphics Driver supports Unified
47 Back Buffer (UBB) and OpenGL Flipping. These features can provide
48 performance gains in certain situations.</p>
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52 <p>Unified Back Buffer (UBB): UBB is available only on the Quadro
53 family of GPUs (Quadro4 NVS excluded) and is enabled by default
54 when there is sufficient video memory available. This can be
55 disabled with the UBB X config option described in <a href=
56 "appendix-b.html" title=
57 "Appendix B. X Config Options">Appendix B, <i>X
58 Config Options</i></a>. When UBB is enabled, all windows share the
59 same back, stencil and depth buffers. When there are many windows,
60 the back, stencil and depth usage will never exceed the size of
61 that used by a full screen window. However, even for a single small
62 window, the back, stencil, and depth video memory usage is that of
63 a full screen window. In that case video memory may be used less
64 efficiently than in the non-UBB case.</p>
67 <p>Flipping: When OpenGL flipping is enabled, OpenGL can perform
68 buffer swaps by changing which buffer the DAC scans out rather than
69 copying the back buffer contents to the front buffer; this is
70 generally a much higher performance mechanism and allows tearless
71 swapping during the vertical retrace (when __GL_SYNC_TO_VBLANK is
72 set). The conditions under which OpenGL can flip are slightly
73 complicated, but in general: on GeForce or newer hardware, OpenGL
74 can flip when a single full screen unobscured OpenGL application is
75 running, and __GL_SYNC_TO_VBLANK is enabled. Additionally, OpenGL
76 can flip on Quadro hardware even when an OpenGL window is partially
77 obscured or not full screen or __GL_SYNC_TO_VBLANK is not
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