force exit of mouseDown?

Bob Sneidar bobs at twft.com
Fri Jun 24 13:33:36 CDT 2011


That would make a good LiveCode article. 

Bob


On Jun 24, 2011, at 10:39 AM, Richard Gaskin wrote:

> Nicolas Cueto wrote:
> 
>> mouseStillDown, for example. When part of a script set as a behavior,
>> mouseStillDown would not work. But that same script with the same
>> mouseStillDown handler, when actually stored as a button's script,
>> worked as expected.
> 
> In a way that's kinda good news, as mouseStillDown is an anomaly among mouse messages.  I think you'll find the other mouse messages quite reliable in behavior scripts, but mouseStillDown is an oddity as noted in the Dictionary:
> 
>     Usually, it is easier and more efficient to use the mouseMove
>     message to track the movement of the mouse while the button
>     is being held down.
> 
>     Note:  If there is no mouseStillDown handler in the target
>     object's script, no mouseStillDown message is sent, even if
>     there is a mouseStillDown handler in an object that's
>     further along the message path.
> 
> Your behavior script should work if you add this to the target object:
> 
> on mouseStillDown
>   pass mouseStillDown
> end mouseStillDown
> 
> Why is mouseStillDown so different from other mouse messages?
> 
> Because it's uniquely inefficient, and the mouseMove message was provided to provide an alternative that's far more flexible and takes fewer system resources for many similar needs.
> 
> Most OSes provide a message when the mouse first goes down, but not all of them provide a second message sent continuously while the mouse is being held down.  So to provide mouseStillDown for us the engine needs to continually poll the OS for the state of the mouse button.   It does this with a frequency defined in the idleRate, which is far less frequent than checking "if the mouse is down" in a repeat loop, but still not optimal.
> 
> If the message was always sent into the message path whether or not it's needed, anytime the user holds the mouse down it would trigger a lot of messaging overhead that's never used.
> 
> But what if you need it?
> 
> Like the idle message (HyperCard's message-clogging workaround for not having timers), all you need to do is include a mouseStillDown handler in any target you want it to be sent to, and the engine will then know to trigger that seldom-used message.
> 
> "Seldom-used?"  Yes:
> 
> Historically, mouseStillDown was most often used for dragging or other operations in which things need to be updated while the mouse is moving.  In such cases, the developer probably doesn't need to update anything until the location of the mouse changes, but mouseStillDown is continually being sent anyway, requiring a lot of redundant processing for things which have no visible effect.
> 
> So the mouseMove message was added, providing a way to update things only when the mouse is moved.
> 
> MouseMove also works when the mouse is up, which can be useful for update mouse position indicators in a drawing program's rulers, for example.
> 
> This additional flexibility requires us to use a few other handlers to substitute for mouseStillDown, but it well worth the few seconds it takes to set up.  You'll need a mouseDown to set a flag so the mouseMove can know that the mouse is down without having to poll the OS (you can also use this flag for other useful info, as shown below), and you'll need mouseUp and mouseRelease messages to clear the flag.
> 
> This example is for a splitter control that adjusts the groups on either side of it:
> 
> local sXOffset
> 
> on mouseDown
>  -- Provide the info mouseMove will need later:
>  put the mouseH - the left of me into sXOffset
> end mouseDown
> 
> on mouseMove
>   -- Is the flag still set?
>   if sXOffset is not empty then
>     -- If so, handle the splitter drag here:
>     set the rect of grp "LeftGroup" to \
>       0,0,the left of me, the height of this cd
>     set the rect of grp "RightGroup" to \
>       the right of me, 0, the width of this cd,
>       the height of this cd
>   end if
> end mouseMove
> 
> -- Clear the flag when the mouse is released over the control:
> on mouseUp
>   put empty into sXOffset
> end mouseUp
> 
> -- Clear the flag when the mouse is release when not over the control:
> on mouseRelease
>  put empty into sXOffset
> end mouseRelease
> 
> 
> In addition to handling simple drags like a splitter, drag-and-drop operations can be handled using the messages provided for those (dragStart, dragMove, dragDrop, dragEnd) far more simply than emulating drag-and-drop behaviors with mouseStillDown.
> 
> So once we use mouseMove for movement-related things and the drag-and-drop messages for those types of actions, the remaining subset of cases where mouseStillDown can be useful are relatively few.  And for those, you can still use it so long as you provide a handler for it in the target object.
> 
> 
>> One other thing I noticed during development and had thought due to my
>> uncertain knowledge about the various mouse-related handlers, was that
>> I couldn't rely on "me" but had to be more specific. Something like
>> "put the short name of the owner of me into tGroup; if the flag of
>> button "theButton" of group tGroup is...", rather than simply "if the
>> flag of me is...".
> 
> More good news:  the uncertainty you subjectively felt is well addressed by the implementation.  If you experiment a bit you'll find that "me" in a behavior script will always refer to the target object.
> 
> Once you've experimented to verify this, you'll become confident with their use and will want to use them every day.  And every night.  And on the weekends.  Highly addictive. :) Behaviors are one of the most powerful additions to the language since arrays.
> 
> 
>> Anyway. I doubt I will ever rely on behaviors again. And I don't feel
>> confident enough with my programming skills to present this to LC as
>> something like a bug. Cause I have been known to be wrong -- though
>> not about mouseStillDown working now when it wasn't before.
> 
> Having addressed the unique anomaly that is the mouseStillDown message, I hope you're inspired to give behaviors a fresh try.
> 
> While your own confidence may not be as strong as the moment, I'm completely confident with with just an hour or two's experimentation to verify how behaviors work, you'll enjoy using them going forward and have simpler and more robust code in the process.
> 
> 
> Hope all is well with you and yours in Tokyo -
> 
> --
> Richard Gaskin
> Fourth World
> LiveCode training and consulting: http://www.fourthworld.com
> Webzine for LiveCode developers: http://www.LiveCodeJournal.com
> LiveCode Journal blog: http://LiveCodejournal.com/blog.irv
> 
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