momObj.prototype.draw =function(){

//lerp x,y 讓大魚跟隨鼠標移動

this.x = lerpDistance(mx,this.x,0.98);//數字越大越慢

this.y = lerpDistance(my,this.y,0.98);

//計算坐標差

//Math.atan2(y,x)

var deltaY = my - this.y;

var deltaX = mx - this.x;

var beta = Math.atan2(deltaY,deltaX);//-pi,pi

//lerp angle 趨向于角度

this.angle = lerpAngle(beta,this.angle,0.6);

ctx1.save();

//使eye, body ,tail的中心在同一個點，后移尾巴位置得到大魚圖片

ctx1.translate(this.x,this.y);//重新映射畫布上的 (0,0) 位置，先移動位置

ctx1.rotate(this.angle);//再旋轉角度

ctx1.drawImage(this.bigTail,-this.bigTail.width * 0.5 + 30,-this.bigTail.height * 0.5);

ctx1.drawImage(this.bigBody,-this.bigBody.width * 0.5,-this.bigBody.height * 0.5);

ctx1.drawImage(this.bigEye,-this.bigEye.width * 0.5,-this.bigEye.height * 0.5);

ctx1.restore();

}