@PadMalcom: a month ago somewhere I found a more easy curve method than Bezier, where all the defining points are on the curve, so it handles better the endpoints. it is called as Catmull-Rom spline, and has functions in DirectX, available in 3DGS d3d9.h, as D3DXVec2CatmullRom, D3DXVec3CatmullRom, and D3DXVec4CatmullRom. (I planned to use it but finally made a more basic solution)
