Message-ID:	<19971017142431.270.qmail@hotmail.com>
From:	"John Patton" <gimli21 AT hotmail DOT com>
To:	djgpp AT delorie DOT com
Cc:	darn AT merlin DOT imag DOT net
Subject:	Re: collision detection
Date:	Fri, 17 Oct 1997 07:24:30 PDT

>From: Darren Grant <darn AT merlin DOT imag DOT net>
>Subject: Re: collision detection
>Date: Thu, 16 Oct 1997 22:10:34 -0700
>Reply-To: darn AT merlin DOT imag DOT net
>To: djgpp AT delorie DOT com
>
>Rob Farley wrote:
>> 
>> >Andrew Deren wrote:
>> >>
>> >> Does anyone know how to detect if two rectangles overlap each 
other at
>> >> some point. Let's say we have something like this:
>
>
>Given two rectangles, A and B, check to see if any of the vertices of B
>lie on A.  If this is true, then there must be overlap.
>
>For collision-detection, you probably want to intersect your velocity
>vectors with the rectangle to determine where the collision occurs.
>


Well, let's 'C',

I've used rectangle collision detection before.  It worked something 
like this:

RECT a, b;

a.top = TopA;
a.left = LeftA;
a.bottom = BottomA;
a.right = RightA;

b.top = TopB;
b.left = LeftB;
b.bottom = BottomB;
b.right = RightB;

...

int collision(RECT *a, RECT *b)
{
   // check if left side of a is inbetween b's right & left
   if (a.left > b.left  &&  a.left < b.right)
   {   // check if the top of a is between b's top and bottom
       if (a.top < b.top && a.top > b.top)
           return TRUE;  // collision!

       // check if the bottom of a is between b's top and bottom
       if (a.bottom < b.top && a.bottom > b.top)
           return TRUE;  // collision!
   }    
   // check if right side of a is between b's left and right
   if (a.right > b.left  &&  a.right < b.right)
   {   // check if the top of a is between b's top and bottom
       if (a.top < b.top && a.top > b.top)
           return TRUE;  // collision!

       // check if the bottom of a is between b's top and bottom
       if (a.bottom < b.top && a.bottom > b.top)
           return TRUE;  // collision!
   }    

// Then do the same thing for b:
   // check if left side of a is inbetween b's right & left
   if (b.left > a.left  &&  b.left < a.right)
   {   // check if the top of a is between b's top and bottom
       if (b.top < a.top && b.top > a.top)
           return TRUE;  // collision!

       // check if the bottom of a is between b's top and bottom
       if (b.bottom < a.top && b.bottom > a.top)
           return TRUE;  // collision!
   }    
   // check if right side of a is between b's left and right
   if (b.right > a.left  &&  b.right < a.right)
   {   // check if the top of a is between b's top and bottom
       if (b.top < a.top && b.top > a.top)
           return TRUE;  // collision!

       // check if the bottom of a is between b's top and bottom
       if (b.bottom < a.top && b.bottom > a.top)
           return TRUE; // collision!
   }    
   return FALSE;  // no collision!
}


I know it's probably not the best method, but of the top of my mind, I 
can't think of any others...


-John

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