3D Graphics And Double Buffering - Asus AGP-V5200 User Manual

3D Graphics and Double Buffering

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16 ASUS AGP-V5200
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The display driver contains an extension to allow 3D applications and the OpenGL
installable client driver (ICD) to drive the AGP-V5200. To provide double buffering
capability for these 3D applications, the display driver offers three features.
A screen-sized off-screen buffer is configured if the
registry variable is 2 ( see explanation later). This buffer is used in 256-color,
32768-color and True Color modes to provide BitBlt double buffering. The off-
screen buffer is also used to provide full screen hardware double buffering if an
application window covers the whole screen. To provide double buffered
accelerated capability, there must be enough memory to contain two frame buffers.
This may not be the case at high resolutions. On the AGP-V5200, the video memory
is separate from the depth buffer/texture memory.
Full Screen Double Buffering
If an application window covers the whole screen, the display driver will
automatically switch to use a hardware double buffer mechanism, which can have
a significant performance benefit. This mechanism will not be available to an
application that has more than a small window border at the top of the screen. It
will also be unavailable if, for example, a floating task bar (common on Windows
NT 4.0) is at any edge other than the top of the screen, since the display driver will
check and find that the application window does not cover the whole screen.
Full Flip Double Buffering
Flip double buffering is available on the AGP-V5200. Flip double buffering is
available for applications that run in a single window and is facilitated by all of
the desktop rendering being written to both frame buffers. When this is available,
only the first double buffered window will use this approach. When there are
multiple double buffered windows, the application reverts to blit double buffering.
Blit Buffering
Blit double buffering is the simplest form and involves copying the contents of the
back buffer into the displayed buffer. For the given configuration, the OpenGL ICD
will always try and use the fastest double buffering method that it can. If the selected
screen resolution/color depth is too high, double buffered applications may start to
run slowly, because they revert to using the Microsoft Generic OpenGL renderer.
DoubleBuffer.NumberOfBuffers