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

' From the book '2d game collision detection'
' circle vs line collision

Import mojo

' This is the collision class.
'
Class collision
    ' Collision function
    ' the circle vs line collision

    Method circle_line_collide:Bool(c:circle,l:line)
        Local lc:vector2d = subtract_vector(c.center,l.base)
        Local p:vector2d = project_vector(lc,l.direction)
        Local nearest:vector2d = add_vector(l.base,p)
        Return circle_point_collide(c,nearest)
    End Method

    Method circle_point_collide:Bool(c:circle,p:vector2d)
        Local distance:vector2d = subtract_vector(c.center,p)
        Return vector_length(distance) <= c.radius
    End Method

    ' Helper Functions ........
    '
    '
    Function vector_length:Float(v:vector2d)
        Return Sqrt(v.x * v.x + v.y * v.y)
    End Function

    Function project_vector:vector2d(project:vector2d, onto:vector2d)
        ' d is a float variable that holds the dot product
        ' of onto,onto
        Local d:Float = dot_product(onto,onto)
        If (0<d)
            ' dp is a variable that holds the dot product
            ' of project and onto
            Local dp:Float = dot_product(project, onto)
            Return multiply_vector(onto,dp/d)
        End If
        Return onto
    End Function
    
    Function multiply_vector:vector2d(v:vector2d,scalar:Float)
        Local r:vector2d = New vector2d()
        r.x = v.x * scalar
        r.y = v.y * scalar
        Return r
    End Function

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

    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 add_vector:vector2d(a:vector2d,b:vector2d)
        Local r:vector2d = New vector2d(0,0)
        r.x = a.x + b.x
        r.y = a.y + b.y
        Return r
    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
    Method draw()
        DrawLine base.x,base.y,direction.x,direction.y
    End Method
End Class

Class circle
    Field center:vector2d
    Field radius:Float
    Method New(center:vector2d,radius:Float)
        Self.center = center
        Self.radius = radius
    End Method
    Method draw()
        DrawCircle center.x,center.y,radius
    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(30)
    End Method
    Method OnUpdate()  
    End Method
    Method OnRender()
        Cls 0,0,0 
        SetColor 255,255,255

        Local cc:vector2d = New vector2d(320,200)
        Local r:Float = 50
        Local circle1:circle = New circle(cc,r)
        Local base:vector2d = New vector2d(0,0)
        Local direction:vector2d = New vector2d(MouseX,MouseY)
        Local l:line = New line(base,direction)
        
        If col.circle_line_collide(circle1,l)
            DrawText "Circle and Line Colliding",0,0
        Else
            DrawText "Circle and Line NOT Colliding",0,0
        End If
        
        circle1.draw
        l.draw
        
        DrawText "Circle vs Line Collision",DeviceWidth/2,0
        DrawText "Info : Lines are infinite in length.",DeviceWidth/2,20
        
    End Method
End Class

Function Main()
    New MyGame()
End Function