Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!rpi!uupsi!sunic!news.funet.fi!funic!santra!hila.hut.fi!jmunkki
From: jmunkki@hila.hut.fi (Juri Munkki)
Newsgroups: comp.sys.mac.programmer
Subject: Re: An itsy bitsy question...
Message-ID: <1991Jan8.043323.954@santra.uucp>
Date: 8 Jan 91 04:33:23 GMT
References: <La6cV1w164w@questor.wimsey.bc.ca> <27725.2787e3d0@kuhub.cc.ukans.edu>
Sender: news@santra.uucp (Cnews - USENET news system)
Reply-To: jmunkki@hila.hut.fi (Juri Munkki)
Organization: Helsinki University of Technology, FINLAND
Lines: 99

In article <27725.2787e3d0@kuhub.cc.ukans.edu> mlab2@kuhub.cc.ukans.edu writes:
>In article <La6cV1w164w@questor.wimsey.bc.ca>, aberno@questor.wimsey.bc.ca (Anthony Berno) writes:
>> How is the "rubberbanding" done in programs like Superpaint when you are 
>> drawing a line on the screen? There isn't an obvious solution in Inside
>> Macintosh, and any solutions I have come up with are hideously difficult.
>> There must be a relatively simple way of doing it. Does anyone out there
>> know?
>> 
>procedure RubberBand;
>  var
>    originalPt, lastPt, newPt : Point;
>begin
>  GetMouse(originalPoint);
>  PenMode(patXOr);
>  GetMouse(lastPt);
>  MoveTo(originalPt.h, originalPt.v);
>  LineTo(lastPt.h, lastPt.v);
>  repeat
>    MoveTo(originalPt.h, originalPt.v);
>    LineTo(lastPt.h, lastPt);
>    GetMouse(newPt);
>    MoveTo(originalPt.h,originalPt.v);
>    LineTo(newPt.h, newPt.v);
>    lastPt:=newPt;
>  until (not Button);
>  PenNormal;
>end; 

Don't do this. I can point out several faults in the above code. First of
all, it creates a quickly flickering line that can be invisible to the
user, if the timing happens to be right. Using exclusive or mode should
be ok in non-paint programs, but inverting a line when the user is trying
to paint a line is not good. Using an offscreen bitmap to restore the
background will look much nicer. Superpaint certainly doesn't use XOR
mode.

Most importantly, even loops like this one should use GetNextEvent.
GetNextEvent will tell you the mouse position as well as the mouse
button state. The nice thing about it is that it can keep track
of button events better than your loop. Your loop fails, if the
user rapidly releases and presses the mouse button. If you have
more than just two lines drawn in the loop, it's quite probable
that this will happen. This also means that you never find out
where the mouse button really came up. Moving the mouse quickly
while releasing the button will get you this result.

I also discovered that the GetMouse/Button approach doesn't really
work with QuicKeys (or at least the version QuicKeys that I have).

Here's what I'm using in Dizzy (a digital circuit simulator that
compiles for Think C and X/Motif on unix machines. It will be soon
released as free software WITH SOURCE CODE.):

/*
>>	Gets the mouse position while in a tracking loop.
>>	Returns true when the mouse button comes up.
*/
int GetMouseTrackEvent(pt)
Point	*pt;
{
	int 	r=0;
	
	r=GetNextEvent(mUpMask+mDownMask,&MyEvent);
	*pt=MyEvent.where;
	GlobalToLocal(pt);
	
	if(r)	r=(MyEvent.what==mouseUp);
	return !r;
}

You also have to check if the mouse moved, if you want to avoid flicker.
Of course this is easy to do with just an extra variable:

	do	/*	Loop until button is released.		*/
	{	downflag = GetMouseTrackEvent(&MousePoint);
		if(MousePoint.h!=OldSpot.h || MousePoint.v !=OldSpot.v)
		{	/* Ok, mouse moved, do the rubberbanding...
			blaa blaa...
			OldSpot = MousePoint;
		}
	}	while(downflag);

I use XOR mode in dizzy, but that's because it has rubberbanding operations
that do not need to be wysiwyg. The interesting thing about loops like
the one above is that they will work with X toolkit just as well, if you
rewrite GetMouseTrackEvent.

As a bonus, this kind of loop allows for multifinder background operations.
If you have terminal program in the background, it will still be able to run
while you rubberband. If you want absolute multifinder compatibility, you
just rewrite GetMouseTrackEvent to use WaitNextEvent. (Sorry, I don't have
a version like that... The only multifinder documents I have are in some
issue of Byte. I wonder why Apple doesn't make stuff like this available
in bookstores or at least technotes.)

   ____________________________________________________________________________
  / Juri Munkki	    /  Helsinki University of Technology   /  Wind  / Project /
 / jmunkki@hut.fi  /  Computing Center Macintosh Support  /  Surf  /  STORM  /
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~