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From: CDCKAB%EMUVM1.BITNET@cunyvm.cuny.edu ( Karl Brendel)
Newsgroups: comp.lang.pascal
Subject: (R)Text windows
Message-ID: <25001@adm.brl.mil>
Date: 14 Nov 90 15:12:05 GMT
Sender: news@adm.brl.mil
Lines: 50


In <7187@hub.ucsb.edu>, Boris Burtin <6600bori@ucsbuxa.ucsb.edu>
  writes:

>I have been working on a text windowing program in Turbo Pascal, and
>just have one question.  I have a function that determines whether two
>windows overlap. It currently does this by checking if one of the
>corners of one of the windows is inside the other window.  The problem
>is that I have not truly optimized the coding.  I have a long string and
>and/or statements that works, but gives me a complex whenever I look at
>it.  Does anyone have an algorithm for this kind of problem?

A simple one published in PC Techniques, v1n2, June/Jul 90, as "Hax 14",
pg 60, from Bryan Flamig:

if a rectangle is type

        rect = record
          xul,yul,           {upper left corner x & y}
          xlr,ylr : integer; {lower right corner x & y}
        end; {rect}

then two rectangles A & B intersect (or windows overlap) if

      A^.xul <= B^.xlr and A^.xlr >= B^.xul
  and A^.yul <= B^.ylr and A^.ylr >= B^.yul

Flamig demonstrates this by drawing examples of the ways in which
rectangles may intersect. You may want to do that also unless the truth
of the statements leaps out at you. ;)

PS--As I look at <zhou@brazil.psych.purdue.edu> Albert Zhou's message
<11473@j.cc.purdue.edu>:

> Suppose two windows are defined as (xa1,ya1,xa2,ya2) and
> (xb1,yb1,xb2,yb2), if (([xa1..xa2]*[xb1..xb2])=[]) or
> ([ya1..ya2]*[yb1..yb2]=[]) then these two windows are not overlapping.

it seems to me that Flamig's solution sort of "falls out" of Albert
Zhou's, and thus may be considered something towards an optimization of
that solution.

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| Karl Brendel                                Centers for Disease Control |
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