Adobe Flash cs4 旋转数学

Question

i am currently having trouble with my object rotating to face another object.currently it works fine as in this picture, my object at the origin will be able to rotate and move to the object in the 3 quadrants except the quadrant with positive 90degrees to 180度，我的 object 在移动到 object 时会旋转几个完整的旋转一段时间，有人知道为什么吗？ 我用来旋转的句子是rotation += (foodLocationDegrees - (rotation - 90)) *.2; 食物是用计算的

var angle:Number = Math.atan2(foodTarget.y - y, foodTarget.x - x); 
            foodLocationDegrees =Math.floor((angle  * 180 / Math.PI));

y和x是鱼的object，foodtarget是食物的object。

 public function moveToFood():void
        {   

            var dx:Number = x - _destinationX;
            var dy:Number = y - _destinationY;

            trace("Food location degree relative to fish mouth "+foodLocationDegrees);
            var targetRotation:Number = 0;
            if (foodLocationDegrees > 0 && foodLocationDegrees < 90)
            {
            trace("food is on 1st quadrant of the fish mount");
                this.x -= dx / 18;
                this.y -= dy / 18;
            }else if (foodLocationDegrees > 90 && foodLocationDegrees < 180)
            {
            trace("food is on 2nd quadrant of the fish mount"); 

                this.x -= dx / 18;
                this.y -= dy / 18;
            }else if (foodLocationDegrees > -180 && foodLocationDegrees < -90)
            {
                trace("food is on 3nd quadrant of the fish mount");

                this.x -= dx / 18;
                this.y -= dy / 18;
            }else if (foodLocationDegrees < 0 && foodLocationDegrees > -90)
            {
                trace("food is on 4nd quadrant of the fish mount");

                this.x -= dx / 18;
                this.y -= dy / 18;
            }
            trace("Before adding Rotation " + rotation);
            var number:Number = (foodLocationDegrees - (rotation - 90)) * .1;
            trace("rotation to add "+number);
            rotation += (foodLocationDegrees - (rotation - 90)) * .2;

            trace("After adding Rotation " + rotation);

            //removing food when both hit boxes hit
            if (hit.hitTestObject(foodTarget.hit))
            {
                foodInPond--;
                foodTarget.removeSelf();
            }

        }

Answer 1

public function moveToFood(food:Food):void
{
    var speed:Number = 6.5;

    var a:Number = food.x - x;
    var b:Number = food.y - y;
    var ang:Number = Math.atan2(b, a);

    rotation = ang * 180 / Math.PI;

    x += Math.cos(ang) * speed;
    y += Math.sin(ang) * speed;
}

你不能只用sin和cos朝着你所面对的方向前进吗？