Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!ucsd!nosc!humu!uhccux!mikem
From: mikem@uhccux.uhcc.hawaii.edu (Mike Morton)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Dissolving BitMaps
Keywords: BitMap Dissolve
Message-ID: <2888@uhccux.uhcc.hawaii.edu>
Date: 26 Dec 88 02:37:18 GMT
References: <17619@vax5.CIT.CORNELL.EDU>
Organization: University of Hawaii
Lines: 36



In a recent article, wing (?) wrote:
> Anybody know a fast way of dissolving one BitMap into another? (like
> HyperCard)  I remember coming across an assembly example but can't find it
> in sumex.  An example in C would be nicer.  I also remember reading
> something about this in Byte, but I can't seem to locate issue.

Some years back, I wrote a subroutine called DissBits, patterned after
CopyBits, which copies the bits from one bitmap to another in a pseudo-
random order, giving the effect of the dissolve.  It's written up in:

    "A Digital Dissolve for Bitmapped Graphics Screens," Dr. Dobb's
    Journal, November '86.
or
    "DissBits: A subroutine to do 'dissolve' shots", MacTutor,
    December '85.

The former article is much more complete, with diagrams and some C code
which is usable on any machine.  (To get real speed, you must use an assembler
version, or copy more than one pixel at a time.)  I mention the latter
article only in case you don't have DDJ.

Caveat: the subroutine works only with bitmaps, not pixmaps.  I've heard
many people discuss using "blending" to fade one picture to another on a
color screen, but haven't seen it done.  I believe that one could apply
the DissBits approach to chunky color screens, and in 8-bit mode it could
even run faster than in 1-bit.  2- and 4-bit would be a pain.

The only source I have for the routine is in Lisa Assembler (remember
TLASM? :-)  If someone has one for the Mac, please feel free to post it
if there's interest (semaphore with me first, to avoid multiple postings?).

 -- Mike Morton // P.O. Box 11378, Honolulu, HI  96828, (808) 676-6966 HST
      Internet: msm@ceta.ics.hawaii.edu
    (anagrams): Mr. Machine Tool; Ethical Mormon; Chosen Immortal; etc.