Big C++: Chptr. 27 -- Graphical User Interfaces

27.7 Painting

Drawing images in a windowing environment is not quite as straightforward as you might think.
- What happens when a user re-sizes the window? ... minimizes the window? ... restores the window?
- What happens when another frame pops up over the image and then vanishes?
The program has no idea when these events will happen.
When they do happen, the window manager knows the contents of the window have been corrupted and sends a paint event to the program.
The program needs to draw the image not just once, but every time a paint even occurs.
All drawing instructions must be placed into a function that is is the target of paint events.
```
EVT_PAINT(EllipseWindow::OnPaint)
```