// forked from _wonder's 3つのセグメントをリーチさせる：IK reach (3)
// forked from _wonder's リーチの仕組み：IK reach (2)
// forked from _wonder's セグメントを描画：IK drag (1)

package  
{
    import flash.display.Sprite;
    import flash.events.Event;
    import flash.geom.Point;
    
    public class InverseKinematics extends Sprite
    {
        private var segments:Array;
        private var num:Number = 5;
        
        public function InverseKinematics() 
        {
            segments = new Array();
            for( var i:uint = 0; i < num; i++ ){
                var seg:Segment = new Segment( 50, 10 );
                addChild( seg );
                segments.push( seg );
            }
            
            seg.x = stage.stageWidth / 2;
            seg.y = stage.stageHeight / 2;

addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
        
        private function onEnterFrame(e:Event):void {
            var target:Point = reach(segments[0], mouseX, mouseY);
            
            for( var i:uint = 1; i < num; i++ ){
                var seg:Segment = segments[i];
                target = reach( seg, target.x, target.y) ;
            }

for( i = num - 1; i > 0; i-- ){
                var segA:Segment = segments[i];
                var segB:Segment = segments[i-1];
                position( segB, segA );
            }
        }
        
        private function reach(seg:Segment, xPos:Number, yPos:Number):Point {
            var dx:Number = xPos - seg.x;
            var dy:Number = yPos - seg.y;
            var angle:Number = Math.atan2( dy, dx );
            seg.rotation = angle * 180 / Math.PI;
            
            var w:Number = seg.getPin().x - seg.x;
            var h:Number = seg.getPin().y - seg.y;
            var tx:Number = xPos - w;
            var ty:Number = yPos - h;
            
            return new Point( tx, ty );
        }

private function position(segA:Segment, segB:Segment):void {
            segA.x = segB.getPin().x;
            segA.y = segB.getPin().y;
        }

}

import flash.display.Sprite;
import flash.geom.Point;

class Segment extends Sprite {
    private var color:uint;
    private var segmentWidth:Number;
    private var segmentHeight:Number;
    
    public var vx:Number = 0;
    public var vy:Number = 0;
    
    public function Segment(segmentWidth:Number,segmentHeight:Number,color:uint=0xffffff){
        this.segmentWidth = segmentWidth;
        this.segmentHeight = segmentHeight;
        this.color = color;
        init();
    }
    
    public function init():void {
        //セグメントの描画
        graphics.lineStyle( 0 );
        graphics.beginFill( color );
        graphics.drawRoundRect( -segmentHeight / 2, -segmentHeight / 2, segmentWidth+segmentHeight, segmentHeight, segmentHeight, segmentHeight );
        graphics.endFill();
        
        //ピン
        graphics.drawCircle( 0, 0, 2 );
        
        graphics.lineStyle( 0, 0xcc0000 );
        graphics.beginFill( 0xcc0000 );
        graphics.drawCircle( segmentWidth, 0, 2 );
    }
    
    public function getPin():Point {
        var angle:Number = rotation * Math.PI / 180;
        var xPos:Number = x + Math.cos( angle ) * segmentWidth;
        var yPos:Number = y + Math.sin( angle ) * segmentWidth;
        return new Point( xPos, yPos );
    }
}

複数のセグメントをリーチさせる：IK reach (4)