鼠标手柄与鼠标不同步

Question

我正在尝试选择一个选择手柄，然后移动它，但鼠标手柄与鼠标指针不同步。

当您选择矩形然后尝试移动中间选择手柄以在矩形中创建间隙时，鼠标指针远离手柄。

小提琴是：http://jsfiddle.net/3PwWY/

                  case 8:
                if(mx > mySel.x + mySel.w/2)
                     mySel.windowWidth = mx - (mySel.x + mySel.w/2);
                else
                      mySel.windowWidth = (mySel.x + mySel.w/2) - mx;


                // Enforce limits on mx:
                //     Should not be closer than 5 pixels to this.x (left side of metric box)
                //     Should not be > this.x + width/2 (middle of metric box)
                  if(mySel.windowWidth < 2*  minGold)
                                           mySel.windowWidth = 2*  minGold;
                console.log(mySel.windowWidth);
                break;
            case 9:
                 if(mx > mySel.x + mySel.w/2)
                     mySel.windowWidth = mx - (mySel.x + mySel.w/2);
                else
                      mySel.windowWidth = (mySel.x + mySel.w/2) - mx;
                // Enforce limits on mx:
                //     Should not be closer than 5 pixels to this.x (left side of metric box)
                //     Should not be > this.x + width/2 (middle of metric box)
              //   mySel.windowWidth = mx - (mySel.x + mySel.w/2);

                console.log(mySel.windowWidth);
                break;