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29
The Ultimate Windows NT Workstation Graphics Accelerator
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In some cases, there is confusion over the meaning of the
PFD_SUPPORT_GDI
bit in the dwFlags field of the PIXELFORMAT descrip-
tor. For instance, 3Dlabs has seen applications, such as
Open Inventor,
that incorrectly assume that if this flag is set, rendering to bitmaps is sup-
ported by the visual. The Installable Client Driver does not support bitmap
rendering so these applications fail. To enable these applications to work
the exporting of
PFD_SUPPORT_GDI
can be disabled by setting the follow-
ing registry variables in
HKEY_LOCAL_MACHINE\SYSTEM\
CurrentControlSet\Services\glint\Device0
to FALSE. The applications will then
choose a Generic pixel format, thereby using unaccelerated software ren-
dering to draw to bitmaps.
3DExtensions.SupportSingle
3DExtensions.SupportDouble
By default,
PFD_SUPPORT_GDI
is set to TRUE for single buffer formats
and FALSE for double buffered formats.
NOTE
Under Windows NT, Generic pixel formats that support double
buffering and rendering by means of GDI are mutually exclusive. This is
because GDI does not have the ability to render to the backbuffer. 3Dlabs
has, therefore, chosen to set the default for double buffering, to be in line
with the Microsoft implementation. However, with care, GDI rendering and
double buffering may be mixed, so the second registry variable will cause
PFD_SUPPORT_GDI
to be exported by double buffer formats, should an
application benefit from this added functionality.
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When running multi-threaded applications, it may be necessary to disable
the use of the fast clear planes by setting the environment variable
GLINT_DONT_USE_FCP
to TRUE, or by checking the corresponding box
in the control panel applet. This issue arises when more than one context is
being used to render to the same window (e.g., OpenGL pipes screen-
saver with multiple option selected). If this variable is set, then this disables
the use of 3Dlabs proprietary fast clear mechanism that allows the depth(Z)
buffer to be cleared up to 16 times more quickly than normal. Typically, this
becomes significant for animation rates of 10Hz or higher in large windows.
