Re: [platform-swt-dev] Mouse events/dragging

[Silenio Quarti <Silenio_Quarti@xxxxxxxxxx>]

We also subclass NSButton and in that
case the NSButton.mouseDown() method needs to be called. It is easy to
know that the super implementation of NSButton needs to be called, but
what about the other leaf widgets we subclass. For example, I seem to remember
that NSOutlineView some times bubbles up the events and some times does
not, depending where you click on the view (expanders, item, blank area).
 If there is a reasonable way of determine when to call super we should
move the code into control.

There is another problem, when super.mouseDown()
is called in NSButton, the button starts a tracking event loop. So no NSButton.mouseMoved()/mouserReleased()
events are delivered until the mouse button is released. Most of the logic
to work around this is in SWTAppliction.nextEventMatchingMask().

Also, NSTrackingArea has a big issue
that it does not handle overlapping widgets. So we were not able to use
it and implement SWT.MouseEnter, SWT.MouseExit events. The current implementation
diffs the current control under the mouse pointer..

Another issue, SWT composites are subclasses
of NSView, so it does not track mouse move events when the mouse button
is pressed on it and dragged. If you move the code into Control, we probably
need to implement something similar to what NSButton does (tracking event
loop).

Silenio

Scott Kovatch <skovatch@xxxxxxxxx>
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09/11/2008 12:47 PM

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Subject	[platform-swt-dev] Mouse events/dragging

Folks,

I’m trying to understand the delivery of mouse events in the Cocoa port.
It looks like there’s a lot of work being done in the Display object that
would be better done in the Control or other subclasses.

I understand how events make it to a window now, but I think that could
also be simplified a bit. It should be sufficient to call [NSApp sendEvent:event]
and have the event go directly to the window targeted by the event. Right
now, Display is trying to get the hit control and then entering a big case
statement based on the event type, and calling mouseDown on the found Widget.
That won’t scale when you throw in all of the kinds of events an NSView
can handle.

Talking to Steve N., he said this is because mouse events were bubbling
up the container hierarchy, but after some code review I see why. In the
Cocoa version of Widget, you’re calling, in effect, [super mouseDown:event]
in the mouseDown handler, as well as making analagous calls to [super <event
handler>]. In the SWT this is probably never what you want to do, though
it’s not uncommon in a Cocoa app. NSViews are a subclass of NSResponder,
and the behavior of super is to send the event to the next handler in the
responder chain. That explains why each parent also sees the event, and
why you may have been generating mouse events on the wrong widget. Subclasses
of Widget may need to override the handler and then call the Java superclass
implementation, but not the Cocoa superclass implementation.

If we take out the calls to callSuper() in all of the Widget base event
handlers you can move much of the code in Display.applicationSendMouseEvent()
into Control, which is where it belongs, IMHO. You might also be able to
get rid of the override of [SWTApplication sendEvent:], since right now
I think it’s just being used as a hook to grab events and dispatch them.

Was there some other problem you were addressing by dispatching the event
yourself? I can look into this today, but I doubt it would be ready before
the current M build.

Scott
--------------- 
Scott Kovatch
Flex Engineering
Adobe Systems, Inc.
skovatch@xxxxxxxxx

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