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Volume 6A: Motif Programming Manual
book

Volume 6A: Motif Programming Manual

by David Brennan, Dan Heller, Paula Ferguson
September 1993
Intermediate to advanced content levelIntermediate to advanced
1014 pages
28h 26m
English
O'Reilly Media, Inc.
Content preview from Volume 6A: Motif Programming Manual
In this example, the ManagerGadget actions don't do anything unless the pointer is inside the Clear button, so the
translation is relatively safe. However, you should be sure to remember that both actions are called. If you press
Button 1 inside the PushButton and doodle around a bit before releasing it, the drawing is still done, even though the
result is hidden by the gadget. In another application, the fact that actions for both the drawing area itself and its
gadget children are both called might lead to indeterminate results.
The draw() action does not (and cannot) know if the gadget is also going to react to the button event. This problem
does not exist with the standard DrawingAreaInput() action routine used in the previous examples because that
routine is implemented by the Motif toolkit and it uses its own internal mechanisms to determine if the gadget is
activated as well. If the DrawingArea does process the event on the gadget, the DrawingAreaInput() action
knows that it should not invoke the callback function. However, this internal mechanism is not available outside of the
widget code. Reordering the action functions does not help, since there is still no way to know, without making an
educated guess, whether or not the DrawingArea acted upon an event on behalf of a gadget child.
As a result of this problem, draw() starts drawing a line, even if it starts in the middle of the PushButton, because
the DrawingArea processes all of the action functions in the list. If you drag the ...
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Publisher Resources

ISBN: 9780596000431