使用CAEmitterLayer在圆圈或CGPath周围绘制粒子

问题描述

我正在尝试使用iOS 5的粒子系统（CAEmitterLayer和CAEmitterCell）来围绕一个圆圈绘制粒子（甚至更好，一个CGPath），但我不知道该怎么做。我能做的最好的是制作一个弧（通过修改CAEmitterCell的yAcceleration属性），但我不能做一个完整的循环。当然，我可以做多个圆弧来模拟圆形，但结非常明显。此外，我不想使用蒙版，因为看起来边缘的粒子被裁剪。任何想法如何做到这一点？

I'm trying to use iOS 5's particle system (CAEmitterLayer and CAEmitterCell) to draw particles around a circle (or even better, a CGPath), but I don't know how to do it. The best I could do is make an arc (by modifying the yAcceleration property of CAEmitterCell), but I can't do a complete circle. Of course, I could do multiple arcs to simulate a circle, but the "knots" are very visible. Also, I don't want to use masks, because it would seem like the particles at the edges are cropped. Any ideas how to do that?

推荐答案

您可以使用CAKeyframeAnimation为emitterPosition设置动画：

You can use a CAKeyframeAnimation to animate the emitterPosition:

CAKeyframeAnimation *particleAnimation = [CAKeyframeAnimation animationWithKeyPath:@"emitterPosition"];
[particleAnimation setPath:yourPath];
[particleAnimation setDuration:1.0];
[particleAnimation setCalculationMode:kCAAnimationPaced];
[yourEmitterLayer addAnimation:particleAnimation forKey:@"yourAnimation"];

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