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IV. UTILITIES & DRIVERS
Full Screen Double Buffering
If an application window covers the whole screen, the display driver will automati-
cally switch to use a hardware double buffer mechanism, which can have a signifi-
cant 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 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.
Color Space Double Buffering
If 4096 colors mode is chosen then hardware double buffering is implemented using
interleaved nibbles. Each pixel is 32 bits deep with the front buffer occupying bits
0x0F0F0F0F and the back buffer occupying bits 0xF0F0F0F0. Switching between
these two buffers is done using the Palette DAC readmask. This is known as Color
Space Double Buffering.
In this mode, standard Windows applications see the display as providing 12 bits per
pixel true color mode with 4 bits per color component. GDI rendering operations are
replicated into both the high and low nibbles. To select this mode choose one of the
4096 color modes from the "List Of Modes" menu in the Display Applet.
Not all 3D Graphics drivers for taking advantage of this mode, though the OpenGL
Installable Client Driver does.
Color Space Double Buffering and OpenGL
The OpenGL Installable Client Driver differentiates between the two buffers by
setting the writemask appropriately. Swapping the buffers over in this instance does
not incur the cost of a blitting operation - the OpenGL buffer swaps over and all the
GDI rendering remains intact. This mode therefore provides the optimal double buff-
ering performance since hardware double buffering is available for all window sizes.
Because the swap operates on the whole screen, there can only be one double buff-
ered OpenGL window that uses this technique. Thus the first 3D window created
can be color space double buffered, while all subsequent 3D windows must use
BitBlt double buffering (assuming there is sufficient VRAM to support another com-
plete screen sized buffer). If the first window closes, the next 3D window created
will use color space double buffering.
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ASUS 3DP-V500TX
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