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Groups > comp.programming > #3172

Re: Calculating coordinate intersections?

From rouben@shady.(none) (Rouben Rostamian)
Newsgroups alt.comp.programming, alt.games.programming, comp.programming
Subject Re: Calculating coordinate intersections?
Date 2013-03-20 05:27 +0000
Organization no organization
Message-ID <kibhbp$cpt$1@news.albasani.net> (permalink)
References <0001HW.CD6E31F4003565A0B04999BF@news.eternal-september.org>

Cross-posted to 3 groups.

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In article <0001HW.CD6E31F4003565A0B04999BF@news.eternal-september.org>,
DaveC  <newsgroups> wrote:
>A point is at X1,Y1. Second point is at X2,Y2.
>
>If point 1 shoots at point 2 (takes a vector in that general direction), how 
>can I know that point 2 was hit?

Suppose you are shooting in the direction of vector V = <V1, V2>.
Let A = <X2 - X1, Y2 - Y1>.

You will hit the target if:
   (a) V is parallel to A;
and
   (b) V has positive components along A.

The first condition is equivalent to A1*V2 = A2*V1.

The second condition is equivalent to A1*V1 + A2*V2 > 0.

-- 
Rouben Rostamian

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Thread

Calculating coordinate intersections? DaveC <invalid@invalid.net> - 2013-03-19 15:17 -0700
  Re: Calculating coordinate intersections? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-03-19 18:26 -0700
    Re: Calculating coordinate intersections? DaveC <invalid@invalid.net> - 2013-03-19 21:53 -0700
      Re: Calculating coordinate intersections? Robert Wessel <robertwessel2@yahoo.com> - 2013-03-20 02:05 -0500
        Re: Calculating coordinate intersections? DaveC <invalid@invalid.net> - 2013-03-20 13:19 -0700
          Re: Calculating coordinate intersections? "BartC" <bc@freeuk.com> - 2013-03-20 21:42 +0000
          Re: Calculating coordinate intersections? Robert Wessel <robertwessel2@yahoo.com> - 2013-03-20 23:48 -0500
  Re: Calculating coordinate intersections? rouben@shady.(none) (Rouben Rostamian) - 2013-03-20 05:27 +0000
    Re: Calculating coordinate intersections? DaveC <invalid@invalid.net> - 2013-03-19 23:39 -0700
      Re: Calculating coordinate intersections? Geoff <geoff@invalid.invalid> - 2013-03-20 00:33 -0700
  Re: Calculating coordinate intersections? James Dow Allen <jdallen2000@yahoo.com> - 2013-03-20 23:41 -0700
    Re: Calculating coordinate intersections? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-03-21 13:18 -0700
      Re: Calculating coordinate intersections? DaveC <invalid@invalid.net> - 2013-03-21 23:02 -0700
        Re: Calculating coordinate intersections? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-03-21 23:28 -0700
    Re: Calculating coordinate intersections? Rui Maciel <rui.maciel@gmail.com> - 2013-03-21 21:40 +0000
      Re: Calculating coordinate intersections? DaveC <invalid@invalid.net> - 2013-03-21 23:03 -0700
        Re: Calculating coordinate intersections? Rui Maciel <rui.maciel@gmail.com> - 2013-03-22 08:36 +0000
          Re: Calculating coordinate intersections? bob <bob@coolfone.comze.com> - 2013-03-22 07:16 -0700
        Re: Calculating coordinate intersections? Geoff <geoff@invalid.invalid> - 2013-03-22 01:49 -0700
  Re: Calculating coordinate intersections? Rui Maciel <rui.maciel@gmail.com> - 2013-03-21 21:26 +0000
    Re: Calculating coordinate intersections? notme <notme@notme.org> - 2013-03-22 00:31 -0700
  Re: Calculating coordinate intersections? "Chris M. Thomasson" <no@spam.invalid> - 2013-03-22 13:08 -0700

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