🔒 Locked

Overlapping rectangles

Started by jamescox3k Dec 19, 2002 at 12:22 PM 5 replies 200+ views

Original Post

Dec 19, 2002 at 12:22 PM

I carn''t rember how this works, say I have 2 rectangles defined like this struct Rect { int x, y, w, h; }; How could i find out if 2 rectngles overlap I''ve got it working with lots of for-loop but shurly theres a mathmatical way of doing it?

Dec 19, 2002 at 12:37 PM

generally:
for every dimension, look if
(lower1 < upper2) AND (upper1 > lower2)

if this condition is satisfied in every dimension, the two axis-aligned volumes (areas, ...) overlap..
for your case the condition is


rect1.x < rect2.x + rect2.w && rect1.x + rect1.w > rect2.x &&
rect1.y < rect2.y + rect2.h && rect1.y + rect1.h > rect2.y

theNestruo

Dec 19, 2002 at 12:42 PM

  
bool areOverlapping (Rect a, Rect b) {
  return ((((a.x  >b.x) && (a.x  <b.x+b.w)) ||
           ((a.x+w>b.x) && (a.x+w<b.x+b.w)))   &&
          (((a.y  >b.y) && (a.y  <b.y+b.h)) ||
           ((a.y+h>b.y) && (a.y+h<b.y+b.h))))
}

Try this. I''m not sure it works (I''ve not tested it). Maybe there are better ways to do it.

theNestruo

Syntax error in 2410
Ok

Dec 19, 2002 at 1:58 PM

theNestruo: your method won''t work correctly...
it returns false if either x or y interval of rectangle b is completely in the according interval of rectangle a...
e.g. if a.x = 0, a.w = 3, b.x = 1, b.w = 1

GA

Arion

Dec 19, 2002 at 2:32 PM

I use this algo for rectangle collision:

    
short int Rect_Rect_Collide ( Rect rect_1, Rect rect_2 )
{
  // Quick Reject Stuff

  if ( rect_1.h < rect_2.y ) return(0);
  if ( rect_1.y > rect_2.h ) return(0);
  if ( rect_1.w < rect_2.x ) return(0);
  if ( rect_1.x > rect_2.w ) return(0);

return(1);
}// end Rect_Rect_Collide

[EDIT] Translated to your Rect structure. [/EDIT]

Guy

[edited by - Arion on December 19, 2002 3:37:12 PM]

Dec 19, 2002 at 3:26 PM

Arion: you should write rect.x + rect.w instead of rect.w and rect.y + rect.h instead of rect.h, h and w are width and height i suppose

GA

Arion

Dec 19, 2002 at 3:41 PM

quote:
Original post by ga
Arion: you should write rect.x + rect.w instead of rect.w and rect.y + rect.h instead of rect.h, h and w are width and height i suppose

GA

Yea, I'm a little confused about the structure.Maybe I can re-write it.

Let's see:

      

short int Rect_Rect_Collide ( Rect rect_1, Rect rect_2 ){

// Quick Reject Stuff


if ( ( rect_1. y + rect_1.h ) <   rect_2.y )              return(0);
if (   rect_1.y               > ( rect_2.y + rect_2.h ) ) return(0);  
if ( ( rect_1.x + rect_1.w )  <   rect_2.x )              return(0);
if (   rect_1.x               > ( rect_2.x + rect_2.w ) ) return(0);

return(1);

}// end Rect_Rect_Collide

Guy

[edited by - Arion on December 19, 2002 4:46:03 PM]

Topic Locked

This topic has been locked by a moderator. New replies are not allowed.