OpenEuphoria

Re: finding if point is inside irregular rectangle

• Posted by Jiri Babor <jbabor at PARADISE.NET.NZ> Feb 28, 2002
• 441 views

Tone,

looking at my five year old code, unearthed by Thomas, I realized the
function can be simplified and, hopefully, made a bit faster as well.

jiri


function inpoly(sequence poly, integer x, integer y)
    -- return 1 (true) if point x,y is inside polygon

    integer m,n,x1,x2,y1,y2

    m = length(poly)
    n = 0
    x2 = poly[m][1]
    y2 = poly[m][2]
    for i = 1 to m do
        x1 = x2
        y1 = y2
        if x = x1 and y = y1 then   -- vertices are tricky...
            return 1
        end if
        x2 = poly[i][1]
        y2 = poly[i][2]
        if y1 = y2 and y = y1 then  -- horizontal side
            if y = y1 then
                return (x1<=x and x2>=x) or (x2<=x and x1>=x)
            end if
        elsif (y1 < y and y2 > y) or (y2 < y and y1 > y) then
            if x > x1 + (x2-x1)*(y-y1)/(y2-y1) then
                n += 1
            end if
        end if
    end for
    return and_bits(n, 1)           -- odd
end function