Chapter 1

12.4 Pointer Processing Revisited
The window server ensures that a pointer event gets to the right window, and the control
environment framework ensures that it gets to the right control. The event can then be
handled by HandlePointerEventL().
12.4.1 Interaction Paradigms
A control should interpret the entire pointer sequence. Two sequences in particular are very
common.
Press-and-release is appropriate for many types of buttons:
� Pen down inside the button: provide visual feedback by making it obvious that the
button is pressed down.
� Pen may stay down and/or be dragged for an arbitrary period.
� Pen up: if the pen is outside the button, release it, redraw it in its neutral state, and do
nothing. If the pen is inside the button, release it, redraw it, and then do the action
associated with the button.
Other related sequences are possible. For instance, UIQ supports buttons that activate as
soon as you press them, whose state toggles, or which expand to show a drop-down list
when pressed, so that you can drag and release on one of the items. There are many
alternatives.
In UIQ, a single tap to select and 'open' is used, where other systems would use double-click
or two taps. Pen down on an item selects and opens it – in the case of COppFleetView,
'open' means 'request a hit on'; in the case of the Application launcher, 'open' means open
the application (or, if its already open, switch to it).
12.4.2 Pick Correlation
Pick correlation means associating the right object with a pointer event. As we saw in
HandlePointerEventL() for COppFleetView at the start of the chapter, this was very
easy to do:
� There is only one object type that could have been selected: a sea tile,
� The object is rectangular,
� The object is part of a simple grid.
This meant that selecting the object was a matter of a simple bounds checking and division.
In more complicated cases (such as selecting text in a word processor, or an object in a
vector graphics package), pick correlation can be an awkward business, and can involve
even more optimization and complexity than is involved in drawing. However, you can use a
few handy techniques to make life easier:
� Object orientation makes designing for pick correlation easier, just as it does most
things.
� Construct a pick list optimized for easy checking when a pointer event occurs.
It so happens that you can often use the same code to handle both incremental redraw and
pick correlation requirements. (You can see this happening quite clearly in
COppFleetView: the precalculated border and tile positions and sizes are used by both
drawing and pick correlation.) The net effect is that your redraw and pick correlation code
can be optimized together. Often, optimizing feels like inventing two solutions to solve one
problem. In this case, one solution solves two problems, which is nice.