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From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Dragging Bitmaps?
Message-ID: <8992@goofy.Apple.COM>
Date: 5 Jul 90 18:24:31 GMT
References: <3398@husc6.harvard.edu>
Organization: Apple Computer, Inc.
Lines: 23

In article <3398@husc6.harvard.edu> siegel@endor.harvard.edu (Rich Siegel) writes:
>
>Does anyone have any suggestions on how to drag small bitmaps around, in the
>same fashion as MacPaint? Currently I drag outlines around, but it would be
>much nicer to move the object as a whole.

The basic approach is to cache the image behind the moving bitmap, and use
that cache to erase the bitmap before it moves.  So the basic code would be
to use 1 CopyBits to erase the old bitmap, and 1 CopyBits to draw the bitmap
in its new position.  (This assumes that you have cached the entire view
beforehand.  This is always better than copying the bits from the screen.)

You will get better results if you do both steps with 1 CopyBits.  To do
this you need another offscreen bitmap the size of the union of the old and
new rectangles.  You initialize this bitmap from the larger cache, and draw
the moving bitmap in its desired position.  Then you use 1 CopyBits to copy
everything onto the screen at once.

-- 
		 Larry Rosenstein,  Object Specialist
 Apple Computer, Inc.  20525 Mariani Ave, MS 46-B  Cupertino, CA 95014
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