Saturday, March 4, 2017

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

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

Import mojo

' This is the collision class.
Class collision
    ' Collision function
    ' the circle vs rectangle segment collision
    Function circle_rectangle_collide:Bool(c:circle,r:rectangle)
        Local clamped:vector2d = clamp_on_rectangle(,r)
        Return circle_point_collide(c,clamped)
    End Function

    ' Needed for circle_segment_collide
    Function circle_point_collide:Bool(c:circle,p:vector2d)
        Local distance:vector2d = subtract_vector(,p)
        Return vector_length(distance) <= c.radius
    End Function

    ' Helper Functions ........
    Function clamp_on_rectangle:vector2d(p:vector2d,r:rectangle)
        Local clamp:vector2d = New vector2d()
        clamp.x = Clamp(p.x,r.origin.x,r.origin.x+r.size.x)
        clamp.y = Clamp(p.y,r.origin.y,r.origin.y+r.size.y)
        Return clamp
    End Function
    Function vector_length:Float(v:vector2d)
        Return Sqrt(v.x * v.x + v.y * v.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
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 circle
    Field center:vector2d
    Field radius:Float
    Method New(center:vector2d,radius:Float) = center
        Self.radius = radius
    End Method
    Method draw()
        DrawCircle center.x,center.y,radius
    End Method
End Class

Class rectangle
    ' origin is a vector that holds the x and y coordinates
    ' of the rectangle
    Field origin:vector2d
    ' size is a vector that holds the x(width) and 
    ' y(height) of the rectangle
    Field size:vector2d
    Method New(origin:vector2d,size:vector2d)
        Self.origin = origin
        Self.size = size
    End Method
    Method draw()
        ' x1,y1,w,h are used to hold the rectangle
        ' location and size.
        Local x1:Int=origin.x
        Local y1:Int=origin.y
        Local w:Int=size.x
        Local h:Int=size.y
        DrawRect x1,y1,w,h
    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()
    End Method
    Method OnUpdate()  
    End Method
    Method OnRender()
        Cls 0,0,0 
        SetColor 255,255,255
        ' Here we set up the circle where we test
        ' the collision with
        Local cc:vector2d = New vector2d(320,200)
        Local r:Float = 50
        Local circle1:circle = New circle(cc,r)
        ' Here we set up the rectangle where we test
        ' the collision with
        Local origin:vector2d = New vector2d(MouseX,MouseY)
        Local size:vector2d = New vector2d(100,100)
        Local rect1:rectangle = New rectangle(origin,size)
        ' Here we call the collision function
        If col.circle_rectangle_collide(circle1,rect1)
            DrawText "Circle Rectangle Colliding",0,0
            DrawText "Circle Rectangle NOT Colliding",0,0
        End If
        ' Draw the circle and rectangle
        DrawText "Move the Mouse to test for Collision",DeviceWidth/2,0
    End Method
End Class

Function Main()
    New MyGame()
End Function

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