Advanced MFC Programming

Chapter 3. Splitter Window
Brush selection can be implemented by calling function CDC::SelectObject(…). This function will
return a pointer to the old brush. After using the brush, we can call this function again and pass the old
brush to it. This will let the old brush be selected into the DC so the new brush is selected out.
When creating a brush, we need to use RGB macro to indicate the brush color. The three parameters of
RGB macro indicate the intensity of red, green and blue colors.
A rectangle can be drawn by calling function CDC::Rectangle(…). We need to pass a CRect type
variable to indicate the position and size of the rectangle.
In the sample, function MCSplitterWnd::OnInvertTracker(…)is implemented as follows:
void MCSplitterWnd::OnInvertTracker(const CRect& rect)
{
CDC* pDC;
CBrush brush;
CBrush *ptrBrushOld;
ASSERT_VALID(this);
ASSERT(!rect.IsRectEmpty());
ASSERT((GetStyle() & WS_CLIPCHILDREN) == 0);
}
pDC=GetDC();
brush.CreateSolidBrush(RGB(255, 0, 0));
ptrBrushOld=pDC->SelectObject(&brush);
pDC->PatBlt(rect.left, rect.top, rect.Width(), rect.Height(), PATINVERT);
pDC->SelectObject(ptrBrushOld);
brush.DeleteObject();
ReleaseDC(pDC);
There is no CDC type pointer passed to this function. However, for any window, its DC could always be
obtained by calling function CWnd::GetDC(). This function will return a pointer to window’s device
context. After we use the DC, we must release it by calling function CWnd::ReleaseDC(…). In function
MCSplitterWnd::OnDrawSplitter(…), first a solid brush with red color is created, then we select it into the
DC, call function CDC::PatBlt(…) to fill the interior of the rectangle using the selected brush.
Function CDC::PatBlt(…) allows us to create a pattern on the device. We can choose different color
output mode: we can copy the brush color to the destination, or we can combine brush color with the color
on the target device using bit-wise operations. The first four parameters of function CDC::PatBlt(…)
indicate the position and size of the rectangle within which we can output the pattern. The fifth parameter
indicates the output mode. In the sample we use PATINVERT drawing mode, this will combine the
destination color and brush color using bit-wise XOR operation. With this mode, the tracker can be easily
erased if it is drawn twice.
Since we use PATINVERT mode to paint the tracker, its color will become the complement color of red
when the user resizes panes using the mouse.
3.5 Splitter Window That Can’t be Resized by Tracking
Sometimes we want each pane of the splitter window to have a fixed size and prevent the user from
resizing the panes through using mouse or keyboard. Since dynamic resizing is a built-in feature of class
CSplitterWnd, whenever we directly derive a class from it, we will automatically have a resizable split bar.
It is not easy to disable this feature because by default, mouse clicking and dragging events will be
processed automatically.
In class CSplitterWnd, four mouse messages are handled to change the state of the split bar: mouse
left button down message WM_LBUTTONDOWN, mouse left button up message WM_LBUTTONUP, mouse move
message WM_MOUSEMOVE, and left button double click message WM_LBUTTONDBLCLK. We need to disable only
the first message handler if we want to disable tracking resize feature (Once the application cannot enter the
tracking state, the rest messages will be processed normally instead of being treated as part of tracking
instructions).
By default, when left button is clicked on a split bar, class CSplitterWnd will respond to this event by
letting the user drag the split bar and place it to a new place. We can bypass this feature by overriding
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