html5+canvas圓形粒子移動背景動畫特效

this.update = function () {
var lastPoint = { x: _this.x, y: _this.y };
// 隨著時間的推移移動點
_this.radians += _this.velocity;

// 拖曳效果
_this.lastMouse.x += (mouse.x - _this.lastMouse.x) * 0.05;
_this.lastMouse.y += (mouse.y - _this.lastMouse.y) * 0.05;

// 圓週運動
_this.distanceFromCenter.x = _this.prevDistanceFromCenter.x + Math.sin(_this.radians) * 100;
_this.distanceFromCenter.y = _this.prevDistanceFromCenter.x + Math.sin(_this.radians) * 100;

_this.x = _this.lastMouse.x + Math.cos(_this.radians) * _this.distanceFromCenter.x;
_this.y = _this.lastMouse.y + Math.sin(_this.radians) * _this.distanceFromCenter.y;

_this.draw(lastPoint);
};