Monkey-X - Collision - Line vs Line - code example

' From the book '2d game collision detection'
' Line vs Line Collision

Import mojo

' This is the collision class. In this example with
' the line vs line method.
'
'
Class collision
    ' Collision function
    Method lines_collide:Bool(a:line,b:line)
        If (parallel_vectors(a.direction,b.direction))
            Return equivalent_lines(a,b)
        Else
            Return True
        End If
    End Method
    ' Helper Functions ........
    '
    '
    Function subtract_vector:vector2d(a:vector2d,b:vector2d)
        Local r:vector2d = New vector2d()
        r.x = a.x - b.x
        r.y = a.y - b.y
        Return r
    End Function

    Function equivalent_lines:Bool(a:line,b:line)
        If (Not parallel_vectors(a.direction,b.direction)) Then Return False
        Local d:vector2d = subtract_vector(a.base,b.base)
        Return parallel_vectors(d,a.direction)
    End Function

    Function equal_vectors:Bool(a:vector2d,b:vector2d)
        Return a.x-b.x = 0 And a.y-b.y = 0
    End Function

    Function parallel_vectors:Bool(a:vector2d,b:vector2d)
        Local na:vector2d = rotate_vector_90(a)    
        Return (0 = Floor(dot_product(na,b)))
    End Function

    Function rotate_vector_90:vector2d(v:vector2d)
        Local r:vector2d = New vector2d()
        r.x = -v.y
        r.y = v.x
        Return r
    End Function

    Function dot_product:Float(a:vector2d,b:vector2d)
        Return a.x * b.x + a.y * b.y 
    End Function
    
End Class

Class vector2d
    ' x and y hold the position of the vector
    Field x:Int,y:Int
    Method New(x:Int,y:Int)
        Self.x = x
        Self.y = y
    End Method
End Class

Class line
    Field base:vector2d
    Field direction:vector2d
    Method New(base:vector2d,direction:vector2d)
        Self.base = base
        Self.direction = direction
    End Method
End Class


' col is the caller of the class collision. 
' we use it to use the collision methods.
Global col:collision = New collision

Class MyGame Extends App

    Method OnCreate()
        SetUpdateRate(60)
    End Method
    Method OnUpdate()        
    End Method
    Method OnRender()
        Cls 0,0,0 
        SetColor 255,255,255
        ' a,b and c are variables that are turned into vectors
        ' using the vector2d class
        Local a:vector2d = New vector2d(30,50)
        Local b:vector2d = New vector2d(30,20)
        Local c:vector2d = New vector2d(80,40)
        Local down:vector2d = New vector2d(50,-10)
        Local up:vector2d = New vector2d(50,20)
        Local l1:line = New line(a,down)
        Local l2:line = New line(a,up)
        Local l3:line = New line(b,up)
        Local l4:line = New line(c,down)

        If col.lines_collide(l1,l2)
            DrawText "Lines 1 and 2 Collide",0,0
            Else
            DrawText "Lines 1 and 2 do not Collide",0,0    
        End If
        If col.lines_collide(l1,l3)
            DrawText "Lines 1 and 3 Collide",0,20
            Else
            DrawText "Lines 1 and 3 do not Collide",0,20
        End If
        If col.lines_collide(l2,l3)
            DrawText "Lines 2 and 3 Collide",0,40
            Else
            DrawText "Lines 2 and 3 do not Collide",0,40
        End If
        If col.lines_collide(l1,l4)
            DrawText "Lines 1 and 4 Collide",0,60
            Else
            DrawText "Lines 1 and 4 do not Collide",0,60
        End If
        '
        DrawText "Line 1 base = "+l1.base.x+","+l1.base.y,100,100
        DrawText "Line 1 direction = "+l1.direction.x+","+l1.direction.y,320,100
        DrawText "Line 2 base = "+l2.base.x+","+l2.base.y,100,120
        DrawText "Line 2 direction = "+l2.direction.x+","+l2.direction.y,320,120
        DrawText "Line 3 base = "+l3.base.x+","+l3.base.y,100,140
        DrawText "Line 3 direction = "+l3.direction.x+","+l3.direction.y,320,140
        DrawText "Line 4 base = "+l4.base.x+","+l4.base.y,100,160
        DrawText "Line 4 direction = "+l4.direction.x+","+l4.direction.y,320,160
        
        '
        DrawText "Line vs Line Collision",DeviceWidth/2,0
        DrawText "Info : Lines are infinite in length",DeviceWidth/2,20
        DrawText "in every direction...",DeviceWidth/2,40
        '                    
    End Method
End Class

Function Main()
    New MyGame()
End Function