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kimos 09-25-2004 03:16 PM

Rectangle intersection
 
hi all,

how to calculate the intersection of 2 rectangle

a rectangle is the following:

Rectangle makeRectangle (Point lowerLeft, Point upperRight) {

Rectangle r;

r.pt1 = lowerLeft;
r.pt2 = upperRight;
return r;
}

and Point is the following:

Point makePoint(int x, int y) {
Point p;
p.x = x;
p.y = y;
return p;
}


And i want the know how to make:

Rectangle intersection(Rectangle r1, Rectangle r2)

this should return the intersection of the 2 rectangles
anyone can help me plz?

Joona I Palaste 09-25-2004 03:49 PM

Re: Rectangle intersection
 
kimos <urdad@hotmail.com> scribbled the following:
> hi all,


> how to calculate the intersection of 2 rectangle


> a rectangle is the following:


> Rectangle makeRectangle (Point lowerLeft, Point upperRight) {
>
> Rectangle r;


> r.pt1 = lowerLeft;
> r.pt2 = upperRight;
> return r;
> }


> and Point is the following:


> Point makePoint(int x, int y) {
> Point p;
> p.x = x;
> p.y = y;
> return p;
> }



> And i want the know how to make:


> Rectangle intersection(Rectangle r1, Rectangle r2)


> this should return the intersection of the 2 rectangles
> anyone can help me plz?


Which part are you having trouble with, calculating the intersection's
coordinates or implementing the algorithm as a C program?

--
/-- Joona Palaste (palaste@cc.helsinki.fi) ------------- Finland --------\
\-- http://www.helsinki.fi/~palaste --------------------- rules! --------/
"Immanuel Kant but Genghis Khan."
- The Official Graffitist's Handbook

Malcolm 09-25-2004 05:02 PM

Re: Rectangle intersection
 

"kimos" <urdad@hotmail.com> wrote in message
news:ae02c0a1.0409250716.99fbf20@posting.google.co m...
> hi all,
>
> how to calculate the intersection of 2 rectangle
>
> a rectangle is the following:
>
> Rectangle makeRectangle (Point lowerLeft, Point upperRight) {
>
> Rectangle r;
>
> r.pt1 = lowerLeft;
> r.pt2 = upperRight;
> return r;
> }
>
> and Point is the following:
>
> Point makePoint(int x, int y) {
> Point p;
> p.x = x;
> p.y = y;
> return p;
> }
>
>
> And i want the know how to make:
>
> Rectangle intersection(Rectangle r1, Rectangle r2)
>
> this should return the intersection of the 2 rectangles
> anyone can help me plz?
>


Rectangle intersection(Rectangle r1, Rectangle r2)
{
Find the leftmost and the bottommost rectangle.
Find the rightmost and the topmost rectangle.

If the left x co-ordinate of the non-leftmost rectangle is between the
left and the right of the leftmost rectangle, you have the left cordinate of
your intersection. If it is to the right you have no intersection, and the
rectangles don't overlap. (If it is to the left you didn't calculate the
leftmost rectangle correctly).

Repeat for all the other coordinates (bottom, right, top).
}



Simon Stienen 09-25-2004 05:11 PM

Re: Rectangle intersection
 
kimos <urdad@hotmail.com> wrote:
> hi all,
>
> how to calculate the intersection of 2 rectangle


Take the rightmost left-border, the left-most right border, the bottom-most
top border and the top-most bottom border as borders for your intersection.
If the left border of the intersection is on the right of the right border
ot the top border below the bottom border, there is no intersection.
--
Simon Stienen <http://dangerouscat.net> <http://slashlife.de>
»What you do in this world is a matter of no consequence,
The question is, what can you make people believe that you have done.«
-- Sherlock Holmes in "A Study in Scarlet" by Sir Arthur Conan Doyle

SM Ryan 09-25-2004 08:51 PM

Re: Rectangle intersection
 
# this should return the intersection of the 2 rectangles
# anyone can help me plz?

Take two pieces of paper, overlay them, and think about you're looking at. Hint:
the intersection is either empty, a point, or a rectangle.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
OOOOOOOOOO! NAVY SEALS!

xarax 09-25-2004 10:52 PM

Re: Rectangle intersection
 

"SM Ryan" <wyrmwif@tango-sierra-oscar-foxtrot-tango.fake.org> wrote in message
news:10lbmj8qmav9hcd@corp.supernews.com...
> # this should return the intersection of the 2 rectangles
> # anyone can help me plz?
>
> Take two pieces of paper, overlay them, and think about you're looking at.

Hint:
> the intersection is either empty, a point, or a rectangle.


Or two points forming a line segment (the
rectangles share some part of a border).



Derrick Coetzee 09-25-2004 11:01 PM

Re: Rectangle intersection
 
kimos wrote:
> how to calculate the intersection of 2 rectangle


The easiest way to think about this problem conceptually is to first
come up with an algorithm for the 1D version, intersecting two line
segments, then generalize it.

Suppose we have a line from a to b and a line from c to d. There are
four cases for intersecting them:

a <= b < c <= d : a----b c----d
In this case the intersection is empty.

a <= b = c <= d : a----b/c----d
In this case the intersection is the single point b=c (the line segment
from b to b.)

a <= c <= b <= d : a---c===b---d
In this case the intersection is the line from c to b.

a <= c <= d <= b : a---c===d---b
In this case the intersection is the line from c to d.

If you simply apply these same four cases to the x and y coordinate
ranges of your rectangles separately, the result will be the x and y
coordinate ranges of the intersection of the rectangles.
--
Derrick Coetzee
I grant this newsgroup posting into the public domain. I disclaim all
express or implied warranty and all liability. I am not a professional.


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