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From: jackiw@cs.swarthmore.edu (Nick Jackiw)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Drawing Analog Clocks
Message-ID: <DZDJG43@xavier.swarthmore.edu>
Date: 2 May 90 14:56:22 GMT
References: <550@fornax.UUCP> <1123@metaphor.Metaphor.COM>
Sender: jeremy@xavier.swarthmore.edu (Jeremy Brest)
Reply-To: jackiw@cs.swarthmore.edu (Nick Jackiw)
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Organization: Visual Geometry Project, Swarthmore College, PA
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rimola@flamingo.metaphor.com (Carlos Rimola) writes:
> There are two parts to these problem: 1) In the Mac environment, how do
> you preserve the previous contents of an arbitrary window area when you
> want to temporarily draw over it (are regions the only option?) and 2)
> What clever algorithms are there for implementing an analog clock.
> 

1) The easiest way is to use patXor mode when drawing your hands. 
Drawing the same thing twice with patXor will leave your background the
way it was before drawing anything.  (Draw once to display, once to 'erase'.)
Unfortunately, this is also the cheesiest method, in that patXor won't
draw your hands as solid black, but rather as some odd intersection of
each hand with its neighbors and with the background.


> BTW, for question 1, I know about off-screen bitmaps but have found
> them to be inefficient when the number of on-screen windows that need
> to be updates is high (e.g. 10 clock windows showing different times).
> 

I find this hard to believe.  Short of writing directly to the screen
memory, nothing will be faster than copyBits if used correctly. If your
bitmapped backgrounds exist offscreen, bit-aligned, at the appropriate
color depth, and registered to unclipped areas of your windows, you can
easily redraw the entire screen in under a second.  The number of
windows on the screen is moot--the number of pixels per screen is fixed.
I posted code on bitmap alignment a while back; there are also technotes
discussing technique.

For the smoothest action possible, I'd recommend

for each clock
	one static bitmap of the clock background
	one scratch bitmap
	your window

All three should be aligned and at the same depth.  Each time you need to
reorient your hands, copy the background into the scratch bitmap, draw the
hands (patCopy) into the scratch bitmap, and then copy the whole thing to
the screen.  Precomputing the endpoints of the hands, rather than using
trigonometric functions while redrawing, will make things considerably
more speedy.


> Please respond via mail if possible..


--
------------------------
Nick Jackiw		jackiw@cs.swarthmore.edu  "Every minute of the future
Visual Geometry Project	jackiw@swarthmr.bitnet     is a memory of the past."
Swarthmore College, PA 19081-1397				-Laivach