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A device-independent bitmap (DIB) is a color bitmap in a format that
eliminates the problems that occur when transferring device-dependent
bitmaps to devices having difference bitmap formats. DIBs provide color and
bitmap information that any display or printer driver can translate into the
proper format for its corresponding device.
 
A display driver can support DIBs by providing the following
device-independent bitmap functions.
 
Function           Description
────────────────────────────────────────────────────────────────────────────
DeviceBitmapBits   Copies a DIB to a device-dependent bitmap or a
                   device-dependent bitmap to a DIB.
 
SetDIBitsToDevice  Copies any portion of a DIB to the screen. This function
                   copies the bits directly without applying a raster
                   operation.
 
StretchDIBits      Moves a source rectangle into a destination rectangle,
                   stretching or compressing the bitmap if necessary to fit
                   the dimensions of the destination rectangle.
 
These functions receive and operate on BITMAPINFO, BITMAPINFOHEADER, and
RGBQUAD structures.
 
A display driver that supports DIBs must provide the CreateDIBitmap function
as well. The function should do nothing more than return zero indicating
that the creation of a DIB is not supported at the driver level.
 
If a display driver supports DIBs, it must set one or more of the
RC_DI_BITMAP, RC_DIBTODEV, and RC_STRETCHDIB values in the dpRaster member
of the GDIINFO structure. If a driver does not set the RC_DI_BITMAP value,
GDI simulates DIB conversions using monochrome bitmaps.
 
Logical-Color Tables
 
A display driver creates a logical-color table when translating a
device-specific bitmap into a DIB. The table resides in the DIB header
block. The device driver, if it is not a palette device, can fill up the
table with whatever color it supports and then, use the corresponding
indexes in the bitmap. The driver must also set the number of colors it is
using in the biClrUsed member of the header block.
 
Consider an example in which the display device is a 4-plane EGA device, and
in which the DIB has 8 bits-per-pixel. The logical color table for the DIB
has provisions for 256 colors, but the 4-plane driver can deal with only 16
colors. The driver would prepare a color table for the DIB that looked like
the following:
 
RGBQUAD ColorTable[] = {
    {0,     0,   0, 0},
    {128,   0,   0, 0},
    {0,   128,   0, 0},
    {128, 128,   0, 0},
    {0,     0, 128, 0},
    {128,   0, 128, 0},
    {0,   128, 128, 0},
    {128, 128, 128, 0},
#ifdef VGA
    {196, 196, 196, 0},
#else /* EGA */
    {64,   64,  64, 0},
#endif
    {255,   0,   0, 0},
    {0,   255,   0, 0},
    {255, 255,   0, 0},
    {0,     0, 255, 0},
    {255,   0, 255, 0},
    {0,   255, 255, 0},
    {255, 255, 255, 0}};
 
The device driver may fill in just 16 colors and set biClrUsed to 16, or it
may fill up entries 16 through 255 with zeros and set biClrUsed to 0.
 
The color-mapping tables for each of the DIB formats can be predefined for a
particular driver and should be copied into the DIB header during the
format-specific initialization.
 
DIB to Device
 
A display driver can copy a DIB directly to the screen using the
SetDIBitsToDevice function. This function saves the trouble of first
converting the DIB into the device-dependent format and then, transferring
it onto the screen. However, only a direct copy of the DIB is provided. For
other raster operations that BitBlt supports, the driver must first convert
the DIB into the internal format. Moreover, only one direction of copy (DIB
to screen) is provided.
 
The process of copying the bits is similar to the one adopted in the
SetDeviceBitmapBits function except that for some devices, such as the
EGA/VGA, the nature of the hardware might make it advantageous to copy one
pixel at a time. The concept of having a color-translation table and
format-specific initialization remains the same.
 
 
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