Saturday, March 4, 2017

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

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

Import mojo

' This is the collision class.
Class collision
    ' Collision function
    ' The rectangle vs Line Collision
    Function line_rectangle_collide:Bool(l:line,r:rectangle)
        Local n:vector2d = rotate_vector_90(l.direction)
        Local dp1:Float,dp2:Float
        Local dp3:Float,dp4:Float
        Local c1:vector2d = r.origin
        Local c2:vector2d = add_vector(c1,r.size)
        Local c3:vector2d = New vector2d(c2.x,c1.y)
        Local c4:vector2d = New vector2d(c1.x,c2.y)
        c1 = subtract_vector(c1,l.base)
        c2 = subtract_vector(c2,l.base)
        c3 = subtract_vector(c3,l.base)
        c4 = subtract_vector(c4,l.base)                        
        dp1 = dot_product(n,c1)
        dp2 = dot_product(n,c2)
        dp3 = dot_product(n,c3)
        dp4 = dot_product(n,c4)
        Return     (dp1 * dp2 <= 0) Or
                (dp2 * dp3 <= 0) Or
                (dp3 * dp4 <= 0)
    End Function

    ' helper functions
    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 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  

    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 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
    Method draw()
        DrawLine base.x,base.y,direction.x,direction.y
    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
    Field angle:Float
    Method OnCreate()
    End Method
    Method OnUpdate()
        If angle > 360 Then angle = 0  
    End Method
    Method OnRender()
        Cls 0,0,0 
        SetColor 255,255,255
        ' this is a line setup
        Local base:vector2d = New vector2d(0,0)
        Local direction:vector2d = New vector2d(MouseX,MouseY)
        Local line1:line = New line(base,direction)
        ' This is the rectangle
        Local origin:vector2d = New vector2d(320,200)
        Local size:vector2d = New vector2d(100,100)
        Local rect1:rectangle = New rectangle(origin,size)

        ' Here we test for collision
        If col.line_rectangle_collide(line1,rect1)
            DrawText "Line vs Rectangle Collision",0,0
            DrawText "Line vs Rectangle NO Collision",0,0
        End If
        ' Here we draw the line and rectangle
        DrawText "Move the Mouse to test for Collision",DeviceWidth/2,0
        DrawText "Info : Lines are infinite in length.",DeviceWidth/2,20
    End Method
End Class

Function Main()
    New MyGame()
End Function

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