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Q140488: HOWTO: How to Determine the Number of Supported Colors

Article: Q140488
Product(s): Microsoft FoxPro
Version(s): WINDOWS:3.0,5.0a,6.0
Operating System(s): 
Keyword(s): kbcode
Last Modified: 30-DEC-1999

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft Visual FoxPro for Windows, versions 3.0, 5.0a, 6.0 
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SUMMARY
=======

Sometimes it is necessary to determine how many colors the current video driver
supports. For example, a distributed application may require 256 color support
so that it will run correctly. This article explains how to retrieve that
information using the GetDC(), GetDeviceCaps(), and ReleaseDC() Windows API
functions.

MORE INFORMATION
================

GetDeviceCaps() is used to determine the number of colors the current video
driver will support. The formula for the number of colors is:

  2^(PLANES * BITSPIXEL)

PLANES is number of color planes that the driver supports, and BITSPIXEL is the
number of adjacent color bits for each pixel. For a more detailed description of
PLANES and BITSPIXEL, please refer to the Visual C++ manual or Help file and the
MSDN compact disc.

Visual FoxPro 3.0/5.0a/6.0 Code Sample
--------------------------------------

The following code can be used in Visual FoxPro for Windows only. See second code
sample for code that works in FoxPro 2.5x and 2.6x.

  * -- 3.0/5.0a/6.0 Code begins here

     DECLARE INTEGER GetDC IN WIN32API INTEGER piGetDC

     iDCHandle = GetDC(0)

     *-- The following are the constants used by GetDeviceCaps
     *-- Additional values can be found in C++ and the MSDN compact disc.
     PLANES = 14
     BITSPIXEL = 12

     DECLARE INTEGER GetDeviceCaps IN WIN32API INTEGER piDCHandle, ;
        INTEGER piNumColors

     iPlanes=GetDeviceCaps(iDCHandle, PLANES)
     iBitsPixel=GetDeviceCaps(iDCHandle,BITSPIXEL)

     *-- Returns the number of colors used by the driver
     iNumColors = 2^(iPlanes * iBitsPixel)
     WAIT WINDOW "Number of colors this driver supports is " ;
        +ALLTRIM(STR(iNumColors))

     *-- The following code releases the GetDC handle
     DECLARE INTEGER ReleaseDC IN Win32API INTEGER piHandle, ;
        INTEGER piDCHandle
     =ReleaseDC(0,iDCHandle)

     *-- 3.0/5.0a/6.0 Code ends here

FoxPro 2.5x and 2.6x Code Sample
--------------------------------

The following code is written for 2.5x and 2.6x versions of FoxPro.

     *-- Code begins here

     SET LIBRARY TO SYS(2004)+"FOXTOOLS.FLL" ADDITIVE

     *-- Gets a Device Context to the video driver. Zero is
     *-- used to get the DC for the screen
     iGetDC = RegFN("GetDC","I","I")
     iDCHandle = CallFN(iGetDC,0)

     *-- The following are the constants used by GetDeviceCaps
     *-- Additional values can be found in C++ and the MSDN compact disc.
     PLANES = 14
     BITSPIXEL = 12

     iGetDevCaps = RegFN("GetDeviceCaps","II","I")
     iPlanes=CallFN(iGetDevCaps,iDCHandle, PLANES)
     iBitsPixel=CallFN(iGetDevCaps,iDCHandle,BITSPIXEL)

     *-- Returns the number of colors used by the driver
     iNumColors = 2^(iPlanes * iBitsPixel)
     WAIT WINDOW "Number of colors this driver supports is ";
          +ALLTRIM(STR(iNumColors))

     *-- The following code releases the GetDC handle
     iReleaseDC = RegFN("ReleaseDC","II","I")
     =CallFN(iReleaseDC,0,iDCHandle)

     RELEASE LIBRARY SYS(2004)+"FOXTOOLS.FLL"
     *-- Code ends here

This code was designed to work under all Windows platforms supported by Microsoft
FoxPro.

Additional query words: VFoxWin

======================================================================
Keywords          : kbcode 
Technology        : kbVFPsearch kbAudDeveloper kbVFP300 kbVFP600 kbVFP500a
Version           : WINDOWS:3.0,5.0a,6.0
Issue type        : kbhowto

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