Microsoft KB Archive/139653

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PRB: Antialiased Polygons Not Drawn in OpenGL Antipoly Sample

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Q139653

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The information in this article applies to:


 * Microsoft Win32 Software Development Kit (SDK), used with:
 * Microsoft Windows NT Server versions 3.51, 4.0
 * Microsoft Windows NT Workstation versions 3.51, 4.0
 * Microsoft Windows 95

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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.

Additional query words: 4.00 Windows

Keywords : kbOSWinNT351 kbOSWinNT400 kbSDKWin32 kbOSWin95

Issue type : kbprb

Technology : kbWin32SDKSearch kbAudDeveloper kbSDKSearch kbWin32sSearch