NoMainWin
Global sw, sh, verts

sw = 640 :   sh = 480
WindowWidth  = sw+8 : WindowHeight = sh+31
UpperLeftX = (DisplayWidth -sw)/2
UpperLeftY = (DisplayHeight-sh)/2
Open"Ray Casting Algorithm" For Graphics_nf_nsb As #g
#g "Down; TrapClose [halt]"
h$ = "#g"

Dim xp(15),yp(15)
#g "when leftButtonDown [halt];when mouseMove checkPoint"
#g "when rightButtonDown [Repeat]"

[Repeat]
    #g "Cls;Fill 32 160 255; Color white;BackColor 32 160 255"
    #g "Place 5 460;\L-click to exit"
    #g "Place 485 460;\R-click for new polygon"

    'generate polygon from random points
    numPoints =  rand(4,15)
    verts = numPoints
    For i = 0 To numPoints-1
        xp(i) = rand(20,620)
        yp(i) = rand(40,420)
    Next
    Call drawPoly h$, verts, "white"
    #g "Flush"
    Wait

[halt]
Close #g
End

'Point In Polygon Function
Function pnp(x, y, numSides)
    j= numSides-1: oddNodes = 0
    For i = 0 To numSides-1
        If ((yp(i)<y) And (yp(j)>=y)) Or ((yp(j)<y) And (yp(i)>=y)) Then
            f1 = y - yp(i):f2 = yp(j) - yp(i): f3 = xp(j) - xp(i)
            If (xp(i) + f1 / f2 * f3) < x Then oddNodes = 1 - oddNodes
        End If
        j = i
    Next
    pnp = oddNodes
End Function

'draw the polygon
Sub drawPoly h$, verts, colour$
    #h$, "Color ";colour$
    j = verts-1
    For i = 0 To verts-1
        #h$ "Line ";xp(j);" ";yp(j);" ";xp(i);" ";yp(i)
        j = i
    Next
End Sub

'change message and color of polygon
Sub checkPoint h$, x, y
    If pnp(x,y,verts) Then
        #h$ "Color 32 160 255;BackColor 32 160 255"
        #h$ "Place 5 0;BoxFilled 150 20;Color white"
        #h$ "Place 7 15;\Mouse In Polygon"
        Call drawPoly h$, verts, "red"
    Else
        #h$ "Color 32 160 255;BackColor 32 160 255"
        #h$ "Place 5 0;BoxFilled 150 20;Color white"
        #h$ "Place 7 15;\Mouse Not In Polygon"
        Call drawPoly h$, verts, "white"
    End If
End Sub

Function rand(loNum,hiNum)
    rand = Int(Rnd(0)*(hiNum-loNum+1)+loNum)
End Function