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From: markv@kuhub.cc.ukans.edu
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Implementing moving crosshair...
Message-ID: <1991Mar22.122651.29232@kuhub.cc.ukans.edu>
Date: 22 Mar 91 18:26:51 GMT
References: <1991Mar22.151348.23800@decuac.dec.com>
Organization: University of Kansas Academic Computing Services
Lines: 49

In article <1991Mar22.151348.23800@decuac.dec.com>, baker@wbc.enet.dec.com writes:
> -Message-Text-Follows-
> 
> 	Given an Intuition window, I want a pair of lines -- one running
> 	from the top to the bottom of the window, the other running from
> 	the left edge to the right edge.  The intersection point of the
> 	lines should track the mouse.
> 
> 	I'm concerned about keeping up with all the MOUSEMOVE's, so I'm
> 	looking for the most efficient way to implement the cross-hair 
> 	lines themselves.  I can use either a Bob for each line, or I can
> 	Draw the lines in COMPLEMENT and move them myself.  Is the use of
> 	a Bob going to make any real difference ?

I think for this a BOB would be harder and slower.  I would draw the
lines in COMPLEMENT (using COMPLEMENT again to remove them of course),
and special case the code to only redraw the cross-hairs if they've
moved and only 3-5 times a sec (the user wont need any more often, but
MOUSEMOVE can spew a lot faster).  I do something similar for another
program.  I've also seem some machines have a fair bit of "jitter" in
the mouse values (it seems to be related to the physical values in the
mouse XY registers being a bit touchcy), so I also use a running
average of the last few (4) values.  Four was picked because I can
keep the running average with integer arithmatic:

	NewAvg = ((OldAvg * 3) + NewVal) >> 2;

or for the speed obsessed:

	NewAvg = ((OldAvg << 1) + OldAvg + NewVal) >> 2;

> 	Also, I'd be interested in any suggestions that would speed up
> 	tracking on rubber-band lines and stretchable bounding-boxes.

Same rules, keep down the number of draws.  Also, pick the color with
complement mode so that you only have to flip bits in one-bitplane.
(JAM1, Color 0 or 1 works well).
 
> 	Thanks much.
> 	 Art Baker
-- 
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