CreateDIBSection

CreateDIBSection

The CreateDIBSection function creates a device-independent bitmap (DIB) that applications can write to directly. The function gives you a pointer to the location of the bitmap's bit values. You can supply a handle to a file mapping object that the function will use to create the bitmap, or you can let the operating system allocate the memory for the bitmap.

HBITMAP CreateDIBSection(

HDC hdc,	// handle to device context
CONST BITMAPINFO *pbmi,	// pointer to structure containing bitmap size, format, and color data
UINT iUsage,	// color data type indicator: RGB values or palette indices
VOID *ppvBits,	// pointer to variable to receive a pointer to the bitmap's bit values
HANDLE hSection,	// optional handle to a file mapping object
DWORD dwOffset	// offset to the bitmap bit values within the file mapping object
);

Parameters

hdc

Handle to a device context. If the value of iUsage is DIB_PAL_COLORS, the function uses this device context's logical palette to initialize the device-independent bitmap's colors.

pbmi

Points to a BITMAPINFO structure that specifies various attributes of the device-independent bitmap, including the bitmap's dimensions and colors.

iUsage

Specifies the type of data contained in the bmiColors array member of the BITMAPINFO structure pointed to by pbmi: logical palette indices or literal RGB values. The following values are defined:

Value	Meaning
DIB_PAL_COLORS	The bmiColors member is an array of 16-bit indices into the logical palette of the device context specified by hdc.
DIB_RGB_COLORS	The BITMAPINFO structure contains an array of literal RGB values.

ppvBits

Points to a variable that receives a pointer to the location of the device-independent bitmap's bit values.

hSection

Handle to a file mapping object that the function will use to create the device-independent bitmap. This parameter can be NULL.

If hSection is not NULL, it must be a handle to a file mapping object created by calling the CreateFileMapping function. Handles created by other means will cause CreateDIBSection to fail.

If hSection is not NULL, the CreateDIBSection function locates the bitmap's bit values at offset dwOffset in the file mapping object referred to by hSection. An application can later retrieve the hSection handle by calling the GetObject function with the HBITMAP returned by CreateDIBSection.

If hSection is NULL, the operating system allocates memory for the device-independent bitmap. In this case, the CreateDIBSection function ignores the dwOffset parameter. An application cannot later obtain a handle to this memory: the dshSection member of the DIBSECTION structure filled in by calling the GetObject function will be NULL.

dwOffset

Specifies the offset from the beginning of the file mapping object referenced by hSection where storage for the bitmap's bit values is to begin. This value is ignored if hSection is NULL. The bitmap's bit values are aligned on doubleword boundaries, so dwOffset must be a multiple of the size of a DWORD.

Return Values

If the function succeeds, the return value is a handle to the newly created device-independent bitmap, and *ppvBits points to the bitmap's bit values.

If the function fails, the return value is NULL, and *ppvBits is NULL. To get extended error information, call GetLastError.

Remarks

As noted above, if hSection is NULL, the operating system allocates memory for the device-independent bitmap. The operating system closes the handle to that memory when you later delete the device-independent bitmap by calling the DeleteObject function. If hSection is not NULL, you must close the hSection memory handle yourself after calling DeleteObject to delete the bitmap.

Windows NT: You need to guarantee that the GDI subsystem has completed any drawing to a bitmap created by CreateDIBSection before you draw to the bitmap yourself. Access to the bitmap must be synchronized. Do this by calling the GdiFlush function. This applies to any use of the pointer to the bitmap's bit values, including passing the pointer in calls to functions such as SetDIBits.