AreaHandler defines the functionality needed for handling events from an Area. Each of the methods on AreaHandler is called from the GUI thread, and every parameter (other than the Area itself) should be assumed to only be valid during the life of the method call (so for instance, do not save AreaDrawParams.AreaWidth, as that might change without generating an event).

Coordinates to Draw and MouseEvent are given in points. Points are generic, floating-point, device-independent coordinates with (0,0) at the top left corner. You never have to worry about the mapping between points and pixels; simply draw everything using points and you get nice effects like looking sharp on high-DPI monitors for free. Proper documentation on the matter is being written. In the meantime, there are several referenes to this kind of drawing, most notably on Apple's website:

For a scrolling Area, points are automatically offset by the scroll position. So if the mouse moves to position (5,5) while the horizontal scrollbar is at position 10 and the horizontal scrollbar is at position 20, the coordinate stored in the AreaMouseEvent structure is (15,25). The same applies to drawing.

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