Question

My Flash application receives B-spline data from an external application but the Flash drawing API only allows quadratic bezier curves using the Graphics#curveTo() method.

Is it possible to convert a B-spline into a series of curveTo() calls?

Answer 1

There are multiple types of B-splines. Still, I imagine you will be splitting the B-spline into Bezier. You would iterate though the curve, and for each one you would traverse the points with a certain detail to be able to draw the curve from lines.

Here’s a quick snippet:

private function curve(control1:Point,anchor1:Point,control2:Point,anchor2:Point,t:Number):Point{
            var result:Point = new Point();
            var tSquared:Number = t*t;
            var tCubed:Number = t*t*t;
            result.x = tCubed*(anchor2.x+3*(control1.x-control2.x)-anchor1.x)
                                        +3*tSquared*(anchor1.x-2*control1.x+control2.x)
                                        +3*y*(control1.x-anchor1.x)+anchor1.x;
            result.y = tCubed*(anchor2.y+3*(control1.y-control2.y)-anchor1.y)
                                        +3*tSquared*(anchor1.y-2*control1.y+control2.y)
                                        +3*y*(control1.y-anchor1.y)+anchor1.y;
            return result;
        }

Have a look at Paul Tondeur’s Drawing a cubic curve blog entry and the references there as well.

HTH