Advanced MFC Programming

Chapter 10. Bitmap
……
……
if(arRgbQuad.GetSize() > 256)
{
while(arRgbQuad.GetSize())
{
delete (LPRGBQUAD)arRgbQuad.GetAt(0);
arRgbQuad.RemoveAt(0);
}
red=green=blue=0;
for(i=0; irgbBlue=blue;
lpRgbQuad->rgbGreen=green;
lpRgbQuad->rgbRed=red;
lpRgbQuad->rgbReserved=0;
if(!(red+=32))if(!(green+=32))blue+=64;
arRgbQuad.Add(lpRgbQuad);
}
bStandardPal=TRUE;
}
else bStandardPal=FALSE;
If the size of color table is greater than 256, we first delete the color table, then create a new color table
that contains only 256 colors. This color table comprises 256 colors that are evenly distributed in a 8×8×4
3-D space, which has the following contents:
(0, 0, 0) (32, 0, 0) (64, 0, 0) … (224, 0, 0)
(0, 32, 0) (32, 32, 0) (64, 0, 0) … (224, 32, 0)
(0, 64, 0, ) (32, 64, 0) (64, 64, 0) … (224, 64, 0)
……
(0, 224, 0, ) (32, 224, 0) (64, 224, 0) … (224, 224, 0)
(0, 0, 64) (32, 0, 64) (64, 0, 64) … (224, 0, 64)
(0, 32, 64) (32, 32, 64) (64, 32, 64) … (224, 32, 64)
(0, 64, 64) (32, 64, 64) (64, 64, 64) … (224, 64, 64)
……
(0, 224, 64) (32, 224, 64) (64, 224, 64) … (224, 224, 64)
……
……
(0, 0, 192) (32, 0, 192) (64, 0, 192) … (224, 0, 192)
(0, 32, 192) (32, 32, 192) (64, 32, 192) … (224, 32, 192)
(0, 64, 192) (32, 64, 192) (64, 64, 192) … (224, 64, 192)
……
(0, 224, 192) (32, 224, 192) (64, 224, 192) … (224, 224, 192)
For a 24-bit color, if we use only 3 most significant bits of red and green colors, and 2 most significant
bits of blue color, and set rest bits to 0. Every possible RGB combination (8 bits for each color) has a
corresponding entry in this table.
We use a flag bStandardPal to indicate which algorithm was used to generate the color table. This is
important because for the two situations the procedure of converting explicit RGB values to indices of
color table is different. If the color table is generated directly from the colors contained in the bitmap (first
case), each pixel can be mapped to an index in the color table by comparing it with every color in the color
table (there must be a hit). Otherwise, we must omit some bits before looking up the color table (second
case).
Following is a portion of function CGDIDoc::OnConvertRGBto256() that allocates buffers from global
memory, fill the buffers with bitmap information header and color table:
……
nSizeCT=256;
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