Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!apple!agate!scam!scott
From: scott@scam.Berkeley.EDU (Scott Silvey)
Newsgroups: comp.sys.mac.programmer
Subject: Tracking the mouse.
Keywords: Interrupts Mouse Tracking
Message-ID: <1990Oct31.100603.1989@agate.berkeley.edu>
Date: 31 Oct 90 10:06:03 GMT
Sender: usenet@agate.berkeley.edu (USENET Administrator)
Reply-To: scott@xcf.berkeley.edu
Organization: UC Berkeley Experimental Computing Facility
Lines: 52


I have just written and debugged my very first Macintosh application!
  It is a simple program which allows you to draw a lot of squiggly
  lines wherever you drag the mouse.  

My problem is that when the user is drawing, the lines come out a bit too
  squiggly.  The mouse skips about erratically like it does when the wait
  cursor shows as the Mac is doing intensive disk I/O.  When the mouse 
  accelleration is high, this problem is the most pronounced, while it is
  reduced when I set the accelleration to 'graphics tablet' mode.  Since
  I may someday wish to make a serious application which tracks the mouse
  smoothly, I find this behaviour rather annoying.  MacPaint and other
  similar programs don't seem to have this trouble, so I can only assume
  I am going about the problem in a manner that is perhaps too brutish.

My speculation is that Mac is going off on some interrupt every few seconds
  or so, resulting in the cursor movement being interpolated over the period
  of time in which the interrupt is being serviced.  Now, I don't even
  know if the Mac even DOES such things ... I'm only guessing.

Does anyone out there perhaps have an idea of what the problem is?  Does
  anyone have code that work as it smoothly tracks the mouse?

I have a Mac SE, I'm using LSC 3.0, and I am NOT using MultiFinder.

Here is the code I use to do the drawing:


          do_line(theEvent)
              EventRecord *theEvent;
          {
              Point p;
          
              p = theEvent->where;
          
              GlobalToLocal(&p);
              MoveTo(p.h, p.v);
          
              do {
                  LineTo(p.h, p.v);
                  GetMouse(&p);
              } while (StillDown());
          
              save_image();
          }


I would appreciate any help you could give me.  

Thanks,

Scott