Advanced MFC Programming

Chapter 8. DC, Pen, Brush and Palette
void CGDIView::OnDraw(CDC *pDC)
{
CPen pen;
CPen *ptrPenOld;
CRect rect;
int i;
}
CGDIDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
GetClientRect(rect);
rect.bottom+=255;
rect.bottom/=256;
for(i=0; iSelectObject(&pen);
pDC->MoveTo(0, rect.top+rect.Height()/2);
pDC->LineTo(rect.right, rect.top);
pDC->SelectObject(ptrPenOld);
pen.DeleteObject();
rect.OffsetRect(0, rect.Height());
}
Instead of creating brushes, solid pens are created to paint the client window area. The width of these
pens is the same with the height of each row, and their colors change gradually from dark blue to bright
blue. Within each loop, before calling functions to draw a line, we select the pen into DC, after the line is
drawn, we select the pen out of the DC. Because a new pen is created in each loop, function
CPen::DeleteObject() is called at the end of the loop. This will destroy the pen so that variable pen can be
initialized again.
Adjusting Display Settings
The two programs must be run on a palette device with a setting of “256 Color” in order to see the
effects of color approximation. Generally this can be adjusted through changing the settings of the system.
We can do this by first opening application Control Panel (Click “Start” menu, go to “Settings”, select
“Control Panel”). Then we ned to double click icon “Display” and click “Setting” tab from the popped up
property sheet. There are a lot of choices in the combo box that is labeled “Color Palette”. Usually it
contains entries such as “24bit”, “256 color”, “16 Color”, etc. The actual available selections depend on the
capability of the video card. If we select “24bit” true color setting, no dithering effect will be seen in the
system. Here we need to choose “256 color” setting in order to test our samples (Figure 8-4).
Choose 256 Color
setting here
Figure 8-4. Setting display
Results
Figure 8-5 and Figure 8-6 show the results from the two color approximation approaches (Please note
that if the samples are executed on non-palette device, we may not see the approximation effect).
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