Tuesday, June 20, 2017

Monkey-X - Closest Point in Line Segment - code example

This can be turned into a collision function. Circle to line segment. Use a 
distance function for that.

' Example on how to get the closest point in a line segment
' to another point.

Import mojo

Class point
    Field x:Float
    Field y:Float
    Method New(x:Float,y:Float)
        Self.x = x
        Self.y = y
    End Method
End Class

Class MyGame Extends App

    Method OnCreate()
    End Method
    Method OnUpdate()        
    End Method
    Method OnRender()
        Cls 0,0,0 
        SetColor 255,255,255        
        DrawText "Mouse the mouse around to see the closest point",0,0
        DrawText "of the line segment..",0,20
        Local mypoint:point = New point(0,0)
        ' the mouse location for point x and y closest to line point
        Local cx:Float=MouseX(),cy:Float=MouseY()
        ' line coordinates
        Local lx1:Float=100
        Local ly1:Float=100
        Local lx2:Float=200
        Local ly2:Float=200
        ' draw the line
        SetColor 100,100,100
        DrawLine lx1,ly1,lx2,ly2
        ' get the closest point on the line segment
        mypoint = getclosestpointonsegment(lx1,ly1,lx2,ly2,cx,cy)
        ' draw this point
           SetColor 255,255,0
           DrawCircle mypoint.x,mypoint.y,10

    End Method
End Class

Function getclosestpointonsegment:point(sx1:Int, sy1:Int, sx2:Int, sy2:Int, px:Int, py:Int)
    Local xDelta:Float = sx2 - sx1
    Local yDelta:Float = sy2 - sy1
    Local u:Float

    If ((xDelta = 0) And (yDelta = 0))    
      Error("Segment start equals segment end")
    End If

    u = ((px - sx1) * xDelta + (py - sy1) * yDelta) / (xDelta * xDelta + yDelta * yDelta)

       Local closestPoint:point = New point(0,0)
    If (u < 0)
      closestPoint = New point(sx1, sy1)
    Else If (u > 1)
      closestPoint = New point(sx2, sy2)
      closestPoint = New point(Int(Floor(sx1 + u * xDelta)), Int(Floor(sy1 + u * yDelta)))
    End If
    Return closestPoint
End Function

Function Main()
    New MyGame()
End Function

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