ID Number: Q79981
1.x 2.x 3.00
WINDOWS
Summary :
Child window controls should not be overlapped in applications for the
Windows operating system. When one control overlaps another control,
or another child window, the borders shared by the controls may not be
drawn properly. Overlapping control may confuse the user of the
application because clicking the mouse in the common area may not
activate the control that the user intended to activate. This behavior
is a consequence of the way that Windows is designed.
More Information :
The following example illustrates the painting problems caused by the
ambiguity of overlapping borders. Consider three edit controls, called
A, B and C, which overlap each other and an enclosing child window D
as shown below:
____________________________________________
| | A | B | C | |
| ---------------------------------------- |
| D |
--------------------------------------------
Assume that control B has the focus. If this set of controls is
covered by another window, which is subsequently moved away, Windows
will send a series of client and nonclient messages to each of the
controls and to the enclosing child window. The result of these
messages may appear as the illustration below, where the portion of
window B's border that overlapped with part of window D's border is
missing:
_______________ ________________
| | A | B | C | |
| ---------------------------------------- |
| D |
--------------------------------------------
Repainting problems related to overlapping controls may vary depending
on the version of Windows used.
Additional reference words: 1.x 2.x 3.00 CS_PARENTDC WS_CLIPCHILDREN
WS_CLIPSIBLINGS WM_NCPAINT WM_PAINT