Exercises
Exercise 25.1: What happens if you don’t clear the cMemoryDC?
Comment out the line _pMemDC->clear(clearrect); from the cGraphicsMFC: :clear(const CRect &clearrect) code in graphicsmfc.h and see what happens. Drag a corner of the window to resize it. Can you figure out what’s going on?
Exercise 25.2: Invalidate and flicker
Change the CPopView:: OnEraseBkgnd method to call the default CView method. Look at the flicker.
Exercise 25.3: Writing your own memory CDC code
Occasionally students rebel at using the cMemoryDC class. ‘I want to use my own code; if I have to do this at our job, I want to be able to do it myself.’ But do keep in mind that the MemoryDC.* files (and all the other software in this book) are well-tested public domain ...
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