Saturday, March 4, 2017

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

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

Import mojo

' This is the collision class.
Class collision
    ' Collision function
    ' Rectangle vs Line Segment Function
    Function rectangle_segment_collide:Bool(r:rectangle,s:segment)
        ' First we test the line vs rectangle collision
        Local sline:line = New line()
        sline.base = s.point1
        sline.direction = subtract_vector(    s.point2,
        If (Not line_rectangle_collide(sline,r)) Then
            Return False
        End If
        ' Here we test the ranges of the line
        ' with the rectangle
        Local rrange:range = New range()
        Local srange:range = New range()
        rrange.minimum = r.origin.x
        rrange.maximum = r.origin.x + r.size.x
        srange.minimum = s.point1.x
        srange.maximum = s.point2.x
        srange = sort_range(srange)
        If(Not overlapping_ranges(rrange,srange)) Then
            Return False
        End If

        rrange.minimum = r.origin.y
        rrange.maximum = r.origin.y + r.size.y
        srange.minimum = s.point1.y
        srange.maximum = s.point2.y
        srange = sort_range(srange)
        Return overlapping_ranges(rrange,srange)
    End Function
    ' The rectangle vs Line Collision
    ' needed for rectangle vs line segment
    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 sort_range:range(r:range)
        Local sorted:range = r
        If (r.minimum > r.maximum)
            sorted.minimum = r.maximum
            sorted.maximum = r.minimum
        End If
        Return sorted
    End Function    

    Function overlapping_ranges:Bool(a:range,b:range)
        Return overlapping(    a.minimum,
    End Function

    Function overlapping:Bool(mina:Float,maxa:Float,minb:Float,maxb:Float)
        Return minb <= maxa And mina <= maxb
    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 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

Class range
    Field minimum:Float
    Field maximum:Float
    Method New(minimum:Float,maximum:Float)
        Self.minimum = minimum
        Self.maximum = maximum
    End Method
End Class

Class segment
    ' point1 and point2 are two vectors.
    ' A vector has a x and y coordinate.
    Field point1:vector2d
    Field point2:vector2d
    Method New(point1:vector2d,point2:vector2d)
        Self.point1 = point1
        Self.point2 = point2
    End Method
    Method draw()
        DrawLine point1.x,point1.y,point2.x,point2.y
    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 segment setup
        Local point1:vector2d = New vector2d(MouseX,MouseY)
        Local point2:vector2d = New vector2d(MouseX+100,MouseY+100)
        ' ls is short for line segment
        Local ls:segment = New segment(point1,point2)
        ' This is the rectangle
        Local origin:vector2d = New vector2d(320,200)
        Local size:vector2d = New vector2d(100,50)
        Local rect1:rectangle = New rectangle(origin,size)

        ' Here we test for collision
        If col.rectangle_segment_collide(rect1,ls)
            DrawText "Rectangle vs Line Segment Collision",0,0
            DrawText "Rectangle vs Line Segment NO Collision",0,0
        End If

        ' Here we draw the line 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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