Advanced MFC Programming

Chapter 13. Adding Special Features to Application
pDC->GetDeviceCaps(LOGPIXELSX),
-pDC->GetDeviceCaps(LOGPIXELSY)
);
pDC->SetViewportOrg(rect.right/2, rect.bottom/2);
rect=CRect(-100, 100, 100, -100);
ptStart.x=rect.right;
ptStart.y=0;
ptEnd.x=(long)(r*cos(nA*2*pi/100));
ptEnd.y=(long)(r*sin(nA*2*pi/100));
brush.CreateSolidBrush(RGB(255, 0, 0));
pBrOld=pDC->SelectObject(&brush);
pDC->Pie(rect, ptStart, ptEnd);
pDC->SelectObject(pBrOld);
brush.DeleteObject();
ptStart=ptEnd;
ptEnd.x=(long)(r*cos((nA+nB)*2*pi/100));
ptEnd.y=(long)(r*sin((nA+nB)*2*pi/100));
brush.CreateSolidBrush(RGB(0, 255, 0));
pBrOld=pDC->SelectObject(&brush);
pDC->Pie(rect, ptStart, ptEnd);
pDC->SelectObject(pBrOld);
brush.DeleteObject();
}
ptStart=ptEnd;
ptEnd.x=(long)(r*cos((nA+nB+nC)*2*pi/100));
ptEnd.y=(long)(r*sin((nA+nB+nC)*2*pi/100));
brush.CreateSolidBrush(RGB(255, 255, 0));
pBrOld=pDC->SelectObject(&brush);
pDC->Pie(rect, ptStart, ptEnd);
pDC->SelectObject(pBrOld);
brush.DeleteObject();
In the above code, first MM_ISOTROPIC mode is set. Then the window extents is set to (100, 100). To
map one logical unit to an absolute size, function CDC::GetDevice(…) is called using both LOGPIXELSX and
LOGPIXELSY parameters. This will cause the function to return the number of pixels per logical inch in both
horizontal and vertical directions. Then we use the returned values to set view port extents. This will cause
100 logical units to be mapped to 1 inch in both horizontal and vertical directions. By doing this, no matter
where we run the program, the output will be the same dimension.
When calling function CDC::SetViewportExt(…), we set the vertical extent to a negative value. This
will change the orientation of the y-axis so that the positive values locate at the upper part of the axis (See
Figure 13-3).
Next, function CDC::SetViewportOrg(…) is called to set the device origin to the center of the window.
This will simplify the calculation of starting and ending points when drawing pies.
13.4 Multiple Documents Implementation
Not only can we implement an application with more than one type of views, but also implement an
application that supports more than one type of documents. For example, generally a graphic editor needs
to support several types of image files, such as bitmap and GIF files. Although we can support all file
formats within one document, for MDI applications, the source code will become easy to manage if we use
one document type to support one file format.
Actually, the procedure of implementing more than one document is almost the same with adding more
than one view to an application. All we need to modify is still function CWinApp::InitInstance(), within
which we must create a new document template and call function CWinApp::AddDocTemplate(…) to bind
the new document (along with a view) to the mainframe window.
From the sample application created in the previous section, we know that when a new document
template is being created, we need to provide a resource ID, a document class name, a view class name, and
a frame window class name. If we look at the menu and icon resources of an MDI application, we will find
that ID IDR_MAINFRAME is used in three different places: there is a string resource using this ID, which will
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