As3中的贝塞尔曲线

Question

Am i right in thinking that from the Flash GUI you can only draw Cubic Bezier Curves, and from Actionscript you can only draw Quadratic Bezier Curves ? Really?

This seems, well.. im sure it cant be.. It would be crazy if i had to write a Quadratic Bezier drawing app to work out some point co-ordinates.

Answer 1

If you're using the drawing API, then you can only draw Quadratic Bezier Curves using the curveTo() function. http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/display/Graphics.html#curveTo ()

For proper bezier curves, it's not that hard, but you'll have to do it yourself. Some quick links with source code that I found: http://www.paultondeur.com/2008/03/09/drawing-a-cubic-bezier-curve-using-actionscript-3/

http://www.farmcode.org/post/2009/07/06/Fast-2D-Bezier-Library-for-ActionScript-3.aspx

Answer 2

Actually from Flash Player 11, released yesterday, the Drawing API supports Cubic Bezier curves:

(amongst other improvements and additions on this major release...)

http://www.adobe.com/devnet/flashplayer/articles/whats-new-flash-player11.html

Answer 3

This is a great post to draw Cubic Bezier curves in ActionScript using the fl.motion.BezierSegment class:

http://www.eleqtriq.com/2010/04/cubic-bezier-in-flash/

It's awesome - I created a complete curve with multiple segments with a fraction of the code and classes you need for most of the other links on this page:

var resolution  :uint       = 50;
var step        :Number     = 1/resolution;

function drawCurve(p0:Point, c0:Point, c1:Point, p1:Point)
{
    var bezier  :BezierSegment  = new BezierSegment(p0, c0, c1, p1);
    var t       :Number         = 0;
    while (t <= 1)
    {
        var pt:Point = bezier.getValue(t);
        with (graphics)
        {
            lineStyle(0.1, 0x00FFFF);
            t == 0
                ? moveTo(pt.x, pt.y)
                : lineTo(pt.x, pt.y);
        }
        t+=step;
    }   
    pt = bezier.getValue(1);
    graphics.lineTo(pt.x, pt.y);    
}

It's a really great post!