PRB: Antialiased Polygons Not Drawn in OpenGL Antipoly Sample (139653)
The information in this article applies to:
- Microsoft Platform Software Development Kit (SDK) 1.0, when used with:
- Microsoft Windows NT Server 3.51
- Microsoft Windows NT Server 4.0
- Microsoft Windows NT Workstation 3.51
- Microsoft Windows NT Workstation 4.0
This article was previously published under Q139653 SYMPTOMS
The antipoly sample in OpenGL SDK BOOK directory is unable to draw
antialised polygons with the generic implementation of Windows NT and
Windows 95 OpenGL.
CAUSE
The technique used in this sample uses alpha values rather than depth
values to determine what to write to the color buffer. You need to first
turn off the depth buffer, choose the (GL_SRC_ALPHA_SATURATE, GL_ONE) blend function, and then draw polygons from front to back. But the generic Windows NT and Windows 95 OpenGL implementation does not provide alpha buffer. The cAlphaBits field of the pixel format descriptor for all generic pixel formats is 0.
RESOLUTION
The sample will work if an OpenGL accelerator card is present and
additional device pixel formats provided by the OpenGL accelerator card
support alpha buffer.
STATUS
This behavior is by design.
| Modification Type: | Minor | Last Reviewed: | 7/11/2005 |
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| Keywords: | kbprb KB139653 |
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