Microsoft KB Archive/85596

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BUG: SETCOLORTABLE Escape Disables Dithering

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Q85596

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) 3.1

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SYMPTOMS
When the VGAPAL video driver is installed on a system, once an application calls the SETCOLORTABLE escape to change an entry in the color table associated with a device context, Windows does not create any dithered brushes for that device context. Instead, Windows returns the solid brush that most closely matches the requested color.

RESOLUTION
To work around this problem, reset the color table to its original state by specifying NULL as the value of the lpInData and lpOutData parameters in a call to the SETCOLORTABLE escape, as follows:

  Escape(hDC, SETCOLORTABLE, 0, NULL, NULL)

STATUS
Microsoft has confirmed this to be a bug in Windows version 3.1. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION
The SETCOLORTABLE escape is documented on pages 500 and 501 of the &quot;Microsoft Software Development Kit: Programmer's Reference, Volume 3: Messages, Structures and Macros&quot; manual.

The comments regarding this escape state the following:


 * The color-mapping algorithms in the display driver will most likely not work with a changed palette.
 * If the color index pointed to by the lpInData parameter is 0xFFFF, the calling application performs all color mapping.
 * Once an application restores the color table to its original state, an application can enable the color-mapping algorithms in the display driver.

However, with the VGAPAL driver, calling the SETCOLORTABLE escape with lpInData pointing to the 0xFFFE value does not restore dithering.

Additional query words: buglist3.10 3.10

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Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK310