OpenEuphoria

Re: finding if point is inside irregular rectangle

• Posted by David Cuny <dcuny at LANSET.COM> Feb 25, 2002
• 573 views

Derek Parnell wrote:

> Not sure if this works for concave polygons.

It should. Odd/Even edge crossing is pretty much the classic method. Plus, 
it's easy to optimize. You don't have to actually cast a ray, you just count 
the number lines that "cover" the point that lie above the point (ie: the x 
of the point lies between (x1, x2) and the one of (y1,y2) lies above the y of 
the point. Something like:

-- p = {x,y}
-- l = { {x1,y1}, {x2,y2}}
function crosses( sequence p, sequence l )
   if l[1][2] >= p[1] or l[2][2] >= p[2] then
      if l[1][1] < l[2][1] then
         return l[1][1] <= p[1] and l[2][1] >= p[1]
      else
         return l[2][1] <= p[1] and l[1][1] >= p[1]
      end if
   end if
   return 0
end function

Untested code, of course. 

-- David Cuny