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From: nujy@vax5.cit.cornell.edu
Newsgroups: comp.graphics
Subject: Re: Graphics -- projectile movement question
Message-ID: <1991Mar27.193157.3660@vax5.cit.cornell.edu>
Date: 27 Mar 91 19:31:57 EDT
References: <1991Mar26.125744.623@stat.appstate.edu> <165722.22170@timbuk.cray.
Distribution: comp
Organization: CIT, Cornell University
Lines: 51

In article <165722.22170@timbuk.cray.com>,
kilian@cray.com (Alan Kilian) writes:
> In article <1991Mar26.125744.623@stat.appstate.edu>,
>     c_s245010114@stat.appstate.edu writes:
>>
>> My question is, what's the best way to devise the arc it will follow using t
>> pixels as the "bomb?" I will generate a random x-position at the bottom of t
>> screen and a random angle of elevation.  The "speed" will be a fixed value
>> which I must mess around with.  "Gravity" will also be a problem.
>>
>>   BITNET:  C_S245010114@appstate.bitnet             Scott E. Schnegelberger
>> INTERNET:  C_S245010114@conrad.appstate.edu Appalachian State University
>
>
> This is easy do do really fast. Here's how:
>
  < psuedocode deleted >
>
> --
>  -Alan Kilian kilian@cray.com                  612.683.5499
>   Cray Research, Inc.           | If you were plowing a field what would
>   655 F Lone Oak Drive          | rather use? 2 strong oxen or 1024 chicke`ns
>   Eagan  MN,     55121          | -Seymour Cray (On massivly paralell machine


I thought you might be interested in more specific initial conditions.
Using Alan's program set:
  xv=cos(angle)*speed
  yv=sin(angle)*speed

Also, in case you're interested, you can make the "bomb" go through two
points on the 'ground' (y=0) and reach a particular height (y=hmax) with
the following equations for yv and gravity.  x0 is the initial x coordinate,
x2 is the final x coordinate, and hmax is the maximum altitude (which
occurs at (x0+x2)/2.  By the way, you can use any xv but it looks best
when it is 1 because the "bomb" moves exactly one pixel horizontally at
each step.

Given:  float xv, x0, x2, hmax

h       = -4.0*hmax / ((x0-x2) * (x0-x2))  /* only used for gravity and yv */
gravity = -2.0*xv*xv*h
yv      = ((x0-x2)*xv + xv*xv) * h
x  = x0
y  = 0.0

Of course, you can optimize this for xv=1.0

  Chris Schoeneman                  |  "I was neat, clean, shaved, and sober,
   nujy@vax5.cit.cornell.edu        |    and I didn't care who knew it."
                                    |               - Raymond Chandler