Initial data commit

Task/Ray-casting-algorithm/Fortran/ray-casting-algorithm-2.f

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+module Ray_Casting_Algo
+  use Polygons
+  implicit none
+
+  real, parameter, private :: eps = 0.00001
+  private :: ray_intersects_seg
+
+contains
+
+  function ray_intersects_seg(p0, a0, b0) result(intersect)
+    type(point), intent(in) :: p0, a0, b0
+    logical :: intersect
+
+    type(point) :: a, b, p
+    real :: m_red, m_blue
+
+    p = p0
+    ! let variable "a" be the point with smallest y coordinate
+    if ( a0%y > b0%y ) then
+       b = a0
+       a = b0
+    else
+       a = a0
+       b = b0
+    end if
+
+    if ( (p%y == a%y) .or. (p%y == b%y) ) p%y = p%y + eps
+
+    intersect = .false.
+
+    if ( (p%y > b%y) .or. (p%y < a%y) ) return
+    if ( p%x > max(a%x, b%x) ) return
+
+    if ( p%x < min(a%x, b%x) ) then
+       intersect = .true.
+    else
+       if ( abs(a%x - b%x) > tiny(a%x) ) then
+          m_red = (b%y - a%y) / (b%x - a%x)
+       else
+          m_red = huge(m_red)
+       end if
+       if ( abs(a%x - p%x) > tiny(a%x) ) then
+          m_blue = (p%y - a%y) / (p%x - a%x)
+       else
+          m_blue = huge(m_blue)
+       end if
+       if ( m_blue >= m_red ) then
+          intersect = .true.
+       else
+          intersect = .false.
+       end if
+    end if
+
+  end function ray_intersects_seg
+
+  function point_is_inside(p, pol) result(inside)
+    logical :: inside
+    type(point), intent(in) :: p
+    type(polygon), intent(in) :: pol
+
+    integer :: i, cnt, pa, pb
+
+    cnt = 0
+    do i = lbound(pol%vertices,1), ubound(pol%vertices,1), 2
+       pa = pol%vertices(i)
+       pb = pol%vertices(i+1)
+       if ( ray_intersects_seg(p, pol%points(pa), pol%points(pb)) ) cnt = cnt + 1
+    end do
+
+    inside = .true.
+    if ( mod(cnt, 2) == 0 ) then
+       inside = .false.
+    end if
+
+  end function point_is_inside
+
+end module Ray_Casting_Algo