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Q74601: INFO: Using GetDIBits()

Article: Q74601
Product(s): Microsoft Windows Software Development Kit
Version(s): 
Operating System(s): 
Keyword(s): kbOSWin310 kbDSupport kbOSWin300 kbSDKWin16
Last Modified: 02-NOV-2001

3.00 3.10
WINDOWS
kbprg

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) for Windows 
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SUMMARY
=======

GetDIBits() retrieves the bits of a specified bitmap and copies them, in
device-independent format, into the buffer that is specified in the lpBits
parameter. If the lpBits parameter is NULL, GetDIBits fills in the BITMAPINFO
data structure to which the lpBitsInfo parameter points, but does not retrieve
bits from the bitmap. The application must ensure that the BITMAPINFO data
structure passed in the GetDIBits call contains valid data before making the
GetDIBits call. This article describes how Windows verifies that the data in the
BITMAPINFO structure is valid.

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

When NULL is specified as the lpBits parameter of GetDIBits, the function will
ensure that the structure passed in to it contains valid data. Then, the
function sets the biSizeImage field of the BITMAPINFOHEADER structure and the
bmiColors field of the BITMAPINFO structure.

To validate the BITMAPINFO structure, the following list outlines the checks that
are made:

     biSize == sizeof(BITMAPINFOHEADER)
     biHeight: high word is 0
     biWidth: high word is 0
     biPlanes == 1
     biBitCount == 1, 4, 8, or 24
     biCompression: high word is 0
     biCompression: low word is 0, BI_RLE8, or BI_RLE4
     if biCompression == BI_RLE8: biBitCount == 8
     if biCompression == BI_RLE4: biBitCount == 4

NOTE: For Windows 95 and Windows NT, the following line

     biBitCount == 1, 4, 8, or 24

should be changed to:

     biBitCount == 1, 4, 8, 16, 24, or 32

All these conditions must be true if GetDIBits is to function correctly and
return valid data (either by setting the biSizeImage field or by returning the
DIB's bits).

If any of these conditions is not true, the header is invalid, and GetDIBits
returns 0 (zero).

GetDIBits is performed on the device driver level. Because different devices may
use different formats to store data, only the device knows its particular
format. Thus, it is the responsibility of the driver to convert the device
format to a device-independent format. If the device driver is not completely
reliable, then GetDIBits may return erroneous information. This should be
considered when using GetDIBits.

Additional query words: 3.00 3.10

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Keywords          : kbOSWin310 kbDSupport kbOSWin300 kbSDKWin16 
Technology        : kbAudDeveloper kbSDKSearch kbWinSDKSearch
Version           : :
Issue type        : kbinfo

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