Date: Sun, 6 Jul 1997 08:00:49 -0400
From: Robert Jasiek <jasiek@berlin.snafu.de>
Subject: Re: Compressed points

> I have a question about compressed points.  If someone sets up a rectangle of
> squares, SQ[bb:dd] and someone with an editor changes one of them to a triangle,
> TR[CC] what should the result be?

A result would be:
;SQ[bb:bd][cb][cd][db:dd]TR[cc]

> 2. Try to break up the original into multiple compressed points.  Anybody know
> a simple algorithm for doing this?

I certainly will not go through the trouble of reinventing an optimal
algorithm for a shortest compressed list now.

Here a compromise (sketch, "bad" performance):

1. Use a 19x19-field. 0=no mark-up, 1=SQ, 2=TR overwrites all else.
2. Initialize all to 0.
3. Mark from decompressed SQ all 1. Empty SQ.
4. Mark from decompressed TR all 2.
5. Keep compressed form of TR.
6. For all y-axis values of field do:
6.1 For all x-axis values of field do:
6.2 If Leftof is <> 1 and field-entry of actual = 1 then add 
[actual:actual] to SQ.
6.3 If Leftof and field-entry of actual are 1 then alter last [m:n] 
of SQ to [m:actual].
6.4 End x
7. End y
8. (A) Until unprocessed property value w in SQ for all of them from 
left to right:
8.1 Let [mn:op] be the actual property value of (A).
8.2 (B) Until unprocessed property value after w in SQ for all of them
from left to right:
8.3 Let [qr:sr] be the actual property value of (B) if r constant.
8.4 If m=q and o=s and r=p+1 then change [mn:op] to [mn:or] and delete
[qr:sr] from SQ.
8.5 End (B).
9. End (A).
10. For all property values of SQ do:
10.1 If actual property value is of type [mn:mn] then change it to [mn].
10.2 End.

-- 
robert jasiek
http://www.inx.de/~jasiek/