For a tile, the weight goes from: [0 ,X0] : 0.0 [X0,X1] : 0.0 to 1.0 [X1,X2] : 1.0 [X2,X3] : 1.0 to 0.0 [X3,SizeX] : 0.0Constructor. Sets to invalid values and must be initialized to reasonable values before using.