Advanced MFC Programming

Chapter 10. Bitmap
Sample 10.1-2\GDI
Sample 10.1-2\GDI demonstrates how to use function CDC::StretchBlt(…) to output the bitmap
image. It is based on sample 10.1-1\GDI. In this sample, the image is enlarged to twice of its original size
and output to the client window.
Because the target image has a bigger dimension now, we need to adjust the scroll sizes. First function
CGDIView::OnInitialUpdate() is modified as follows for this purpose:
……
void CGDIView::OnInitialUpdate()
{
SetScrollSizes(MM_TEXT, CSize(2*bm.bmWidth, 2*bm.bmHeight));
}
CScrollView::OnInitialUpdate();
The scroll sizes are set to twice of the bitmap size.
Function CDC::StretchBlt(…) has 10 parameters:
BOOL CDC::StretchBlt
(
int x, int y, int nWidth, int nHeight,
CDC *pSrcDC,
int xSrc, int ySrc, int nSrcWidth, int nSrcHeight,
DWORD dwRop
);
There are two extra parameters nSrcWidth and nSrcHeight here (compared to function
CDC::BitBlt()), which specify the extent of original bitmap that will be output to the target. Obviously,
nWidth and nSrcWidth determine the horizontal ratio of the output bitmap (relative to source bitmap).
Likewise, nHeight and nSrcHeight determine the vertical ratio.
In the sample, both horizontal and vertical ratios are set to 200%, and function CGDIView::OnDraw(…)
is modified as follows:
……
void CGDIView::OnDraw(CDC *pDC)
{
}
pDC->StretchBlt
(
0,
0,
2*bm.bmWidth,
2*bm.bmHeight,
&dcMemory,
0,
0,
bm.bmWidth,
bm.bmHeight,
SRCCOPY
);
dcMemory.SelectObject(pBmpOld);
With the above modifications, we will have an enlarged bitmap image in the client window.
10.2 Extracting Palette from DIB
If we execute the previous two samples on a palette device, we may experience color distortion (Please
open file 10.1-1\bitmap.bmp using a standard graphic editor and compare the results). This is because we
didn’t implement logic palette for displaying the bitmap, so the the colors of the bitmap pixels are mapped
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