Task: Ray-casting algorithm







Python: from collections import namedtuple
from pprint import pprint as pp
import sys

Pt = namedtuple('Pt', 'x, y')               
Edge = namedtuple('Edge', 'a, b')           
Poly = namedtuple('Poly', 'name, edges')    

_eps = 0.00001
_huge = sys.float_info.max
_tiny = sys.float_info.min

def rayintersectseg(p, edge):
    
    a,b = edge
    if a.y > b.y:
        a,b = b,a
    if p.y == a.y or p.y == b.y:
        p = Pt(p.x, p.y + _eps)

    intersect = False

    if (p.y > b.y or p.y < a.y) or (
        p.x > max(a.x, b.x)):
        return False

    if p.x < min(a.x, b.x):
        intersect = True
    else:
        if abs(a.x - b.x) > _tiny:
            m_red = (b.y - a.y) / float(b.x - a.x)
        else:
            m_red = _huge
        if abs(a.x - p.x) > _tiny:
            m_blue = (p.y - a.y) / float(p.x - a.x)
        else:
            m_blue = _huge
        intersect = m_blue >= m_red
    return intersect

def _odd(x): return x%2 == 1

def ispointinside(p, poly):
    ln = len(poly)
    return _odd(sum(rayintersectseg(p, edge)
                    for edge in poly.edges ))

def polypp(poly):
    print ("\n  Polygon(name='%s', edges=(" % poly.name)
    print ('   ', ',\n    '.join(str(e) for e in poly.edges) + '\n    ))')

if __name__ == '__main__':
    polys = [
      Poly(name='square', edges=(
        Edge(a=Pt(x=0, y=0), b=Pt(x=10, y=0)),
        Edge(a=Pt(x=10, y=0), b=Pt(x=10, y=10)),
        Edge(a=Pt(x=10, y=10), b=Pt(x=0, y=10)),
        Edge(a=Pt(x=0, y=10), b=Pt(x=0, y=0))
        )),
      Poly(name='square_hole', edges=(
        Edge(a=Pt(x=0, y=0), b=Pt(x=10, y=0)),
        Edge(a=Pt(x=10, y=0), b=Pt(x=10, y=10)),
        Edge(a=Pt(x=10, y=10), b=Pt(x=0, y=10)),
        Edge(a=Pt(x=0, y=10), b=Pt(x=0, y=0)),
        Edge(a=Pt(x=2.5, y=2.5), b=Pt(x=7.5, y=2.5)),
        Edge(a=Pt(x=7.5, y=2.5), b=Pt(x=7.5, y=7.5)),
        Edge(a=Pt(x=7.5, y=7.5), b=Pt(x=2.5, y=7.5)),
        Edge(a=Pt(x=2.5, y=7.5), b=Pt(x=2.5, y=2.5))
        )),
      Poly(name='strange', edges=(
        Edge(a=Pt(x=0, y=0), b=Pt(x=2.5, y=2.5)),
        Edge(a=Pt(x=2.5, y=2.5), b=Pt(x=0, y=10)),
        Edge(a=Pt(x=0, y=10), b=Pt(x=2.5, y=7.5)),
        Edge(a=Pt(x=2.5, y=7.5), b=Pt(x=7.5, y=7.5)),
        Edge(a=Pt(x=7.5, y=7.5), b=Pt(x=10, y=10)),
        Edge(a=Pt(x=10, y=10), b=Pt(x=10, y=0)),
        Edge(a=Pt(x=10, y=0), b=Pt(x=2.5, y=2.5))
        )),
      Poly(name='exagon', edges=(
        Edge(a=Pt(x=3, y=0), b=Pt(x=7, y=0)),
        Edge(a=Pt(x=7, y=0), b=Pt(x=10, y=5)),
        Edge(a=Pt(x=10, y=5), b=Pt(x=7, y=10)),
        Edge(a=Pt(x=7, y=10), b=Pt(x=3, y=10)),
        Edge(a=Pt(x=3, y=10), b=Pt(x=0, y=5)),
        Edge(a=Pt(x=0, y=5), b=Pt(x=3, y=0))
        )),
      ]
    testpoints = (Pt(x=5, y=5), Pt(x=5, y=8),
                  Pt(x=-10, y=5), Pt(x=0, y=5),
                  Pt(x=10, y=5), Pt(x=8, y=5),
                  Pt(x=10, y=10))
    
    print ("\n TESTING WHETHER POINTS ARE WITHIN POLYGONS")
    for poly in polys:
        polypp(poly)
        print ('   ', '\t'.join("%s: %s" % (p, ispointinside(p, poly))
                               for p in testpoints[:3]))
        print ('   ', '\t'.join("%s: %s" % (p, ispointinside(p, poly))
                               for p in testpoints[3:6]))
        print ('   ', '\t'.join("%s: %s" % (p, ispointinside(p, poly))
                               for p in testpoints[6:]))


VB: Imports System.Math

Module RayCasting

    Private square As Integer()() = {New Integer() {0, 0}, New Integer() {20, 0}, New Integer() {20, 20}, New Integer() {0, 20}}
    Private squareHole As Integer()() = {New Integer() {0, 0}, New Integer() {20, 0}, New Integer() {20, 20}, New Integer() {0, 20}, New Integer() {5, 5}, New Integer() {15, 5}, New Integer() {15, 15}, New Integer() {5, 15}}
    Private strange As Integer()() = {New Integer() {0, 0}, New Integer() {5, 5}, New Integer() {0, 20}, New Integer() {5, 15}, New Integer() {15, 15}, New Integer() {20, 20}, New Integer() {20, 0}}
    Private hexagon As Integer()() = {New Integer() {6, 0}, New Integer() {14, 0}, New Integer() {20, 10}, New Integer() {14, 20}, New Integer() {6, 20}, New Integer() {0, 10}}
    Private shapes As Integer()()() = {square, squareHole, strange, hexagon}

    Public Sub Main()
        Dim testPoints As Double()() = {New Double() {10, 10}, New Double() {10, 16}, New Double() {-20, 10}, New Double() {0, 10}, New Double() {20, 10}, New Double() {16, 10}, New Double() {20, 20}}

        For Each shape As Integer()() In shapes
            For Each point As Double() In testPoints
                Console.Write(String.Format("{0} ", Contains(shape, point).ToString.PadLeft(7)))
            Next
            Console.WriteLine()
        Next
    End Sub

    Private Function Contains(shape As Integer()(), point As Double()) As Boolean

        Dim inside As Boolean = False
        Dim length As Integer = shape.Length

        For i As Integer = 0 To length - 1
            If Intersects(shape(i), shape((i + 1) Mod length), point) Then
                inside = Not inside
            End If
        Next

        Return inside
    End Function

    Private Function Intersects(a As Integer(), b As Integer(), p As Double()) As Boolean

        If a(1) > b(1) Then Return Intersects(b, a, p)
        If p(1) = a(1) Or p(1) = b(1) Then p(1) += 0.0001
        If p(1) > b(1) Or p(1) < a(1) Or p(0) >= Max(a(0), b(0)) Then Return False
        If p(0) < Min(a(0), b(0)) Then Return True
        Dim red As Double = (p(1) - a(1)) / (p(0) - a(0))
        Dim blue As Double = (b(1) - a(1)) / (b(0) - a(0))

        Return red >= blue
    End Function
End Module