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Operation (Windows NT)
PowerStorm 300 AGP and 300/350 PCI Graphics Controllers 5–17
•
Blending, using a destination alpha value
The application needs an alpha buffer if it calls the glBlendFunc function with one of
the following values:
–
DST_ALPHA
–
ONE_MINUS_DST_ALPHA
–
ONE_MINUS_DST_COLOR
–
SRC_ALPHA_SATURATE
In conformance with OpenGL, glReadPixels returns 1.0 for all alpha values, and OpenGL
uses 1.0 for all destination alpha values when computing blending factors.
Note that all alpha related aspects of the rasterization and per-fragment portions of the
OpenGL pipeline (blending, alpha test, alpha related texturing functionality) are supported
by PowerStorm 300/350 PCI graphics controllers on the Windows NT Alpha platform.
_________________________Caution ___________________________
If an application calls wglChoosePixelFormat to request a pixel format with
alpha planes, a generic pixel format will be chosen. In this case OpenGL
operations will not be hardware accelerated, thus severely degrading
performance.
____________________________________________________________
5.3.3.2.3 Overlay Planes
PowerStorm 300/350 PCI graphics controllers on the Windows NT Alpha platform provide
hardware support for 8-bit, double-buffered overlay planes. Note that for performance
reasons, not all pixel formats support overlay planes. If you do not require overlay planes,
selecting a pixel format without overlay support will ensure maximum performance.
5.3.3.2.4 Stencil Planes
The PowerStorm display driver provides hardware support for a 4-bit stencil buffer. Note
that for performance reasons, not all pixel formats support stencil planes. If you do not
require stencil planes, selecting a pixel format without stencil planes will ensure maximum
performance. The availability of pixel formats with stencil planes can be disabled by
using the Display Applet.
5.3.3.2.5 SoftImage Customizations
When using PowerStorm 300/350 PCI graphics controllers on the Windows NT Alpha
platform with Microsoft’s SoftImage, you should enable SoftImage Customizations using
the Display Applet. This will ensure maximum performance and compatibility with
SoftImage.