Advanced MFC Programming

Chapter 11. Sample: Simple Paint
Figure 11.8 A Path
A path can record almost all types of outputs to the device context. Like other GDI objects, it must be
first selected into a DC before being used. However, there is no class such as CPath that lets us declare a
path type variable. Therefore, we can not select a path into DC by calling function CDC::
SelectObject(…). To use path, we must call function CDC::BeginPath() to start path recording and call
CDC::EndPath() to end it.
Between the above two functions, we can call any of the drawing functions such as CDC::LineTo(…),
CDC::Rectangle(…), and CDC::TextOut(…). The trace of the output will be recorded in the path and can be
rendered later. When rendering the recorded path, we can either draw only the outline of the path using the
selected pen or fill the interior with the selected brush, or we can do both.
The following functions can be used to implement these path drawing:
BOOL CDC::StrokePath();
BOOL CDC::FillPath();
BOOL CDC::StrokeAndFillPath();
Function CDC::StrokePath() will render a specific path using the currently selected pen. This will
draw outline of the closed figure. Function CDC::FillPath() will close any open figures in the path and fill
its interior using the currently selected brush. After the interior is filled, the path will be discarded from the
device context. Function CDC::StrokeAndFillPath() implements both: it will stroke the outline of the path
and fill the interior.
Please note that the last function can not be replaced by calling the first two functions consecutively.
After function CDC::StrokePath() is called, the path will be discarded, so further calling
CDC::FillPath() will not have any effect.
Path & Region
Region can also be created from path. One straightforward method is to call function CDC::
SelectClipPath(…) to create a region from the current path then select it into the DC. If we create region
this way, there is no need for us to use CRgn type variable. Also, we can explicitly create a region from the
path by calling function CRgn::CreateFromPath(…). The parameter we need to pass to this function is a
pointer to the DC that contains the path. This is a very powerful method: by creating an irregular-shaped
path, we can use it to create a region that can be used to confine the output of DC.
Sample 11.7-1\GDI
Sample 11.7-1\GDI demonstrates path implementation. It is a standard SDI application generated by
Application Wizard. No new variable is declared. In function CGDIView::OnDraw(…), we begin path
recording and output four characters ‘P’, ‘a’, ‘t’, ‘h’ to the client window. Then we stroke the outlines of
the four characters and fill the path with a hatched brush.
In the sample, the font used to output the text is “Times New Roman”, and its height is 400. The brush
used to fill the interior of the path is a hatched brush whose pattern is cross hatch at 45 degrees. Between
function CDC::BeginPath() and CDC::EndPath(), there is only one statement that calls function
CDC::TextOut(…) to output the four characters. Please note that while path recording is undergoing, no
output will be generated to the target device. So this will not output anything to the client window. Finally
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