Chapter 1

The two points that define Trect can be interpreted by specific graphics implementations in
different ways. One common interpretation is to place the top-left point inside the rectangle,
and the bottom-right point is just outside it, as shown in Figure 11.4:
Figure 11.4
This definition makes some things easier, such as calculating the size, because you simply
subtract the x and y coordinates of the top-left from the bottom-right point. It also makes
other things harder, such as rubber- banding calculations for interactively drawing a
rectangle, because you have to add (1, 1) to the pointer coordinates to include the bottomright
corner correctly. If TRect is defined to include its bottom-right corner, it simply makes
different things easier and different things harder. It's important to remember that the
definition of the rectangle depends on the specific graphics interpretation.
Rectangles should be normalized, so that iTl coordinates are never greater than
corresponding iBr coordinates. If you perform a calculation on a TRect that might violate
this condition, call Normalize() to clear things up, by swapping the x coordinate values
and/or y coordinate values as necessary.
Region-related classes
Several region-related classes are also defined in e32std.h. These define a region of
arbitrary shape as the union of several rectangles. The region classes are used extensively
by the window server, but only in specialized application programs.
A region can potentially have very many rectangles so that the region classes, in general,
can allocate resources on the heap. They are heavily optimized so that, if only relatively few
rectangles are needed to define the region, then no heap-based allocation is necessary. So,
while points, rectangles, and sizes are simple, T classes that are easy to allocate anywhere
and pass around in client-server call's regions require more careful management and like C
classes, need to be deleted or cleaned up when no longer required.
11.2.2 Setting up the Graphics Context
CGraphicsContext holds several important items of context for drawing functions:
� Pen
� Brush
� Font
� Current position
� Origin
� Clipping Region
� Justification.