简单同心圆效果

#import "BNRHypnosisView.h"

@implementation BNRHypnosisView
- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if(self)
    {
        self.backgroundColor = [UIColor clearColor];
    }
    return  self;
}
- (void)drawRect:(CGRect)rect
{
    CGRect bounds = self.bounds;
    
    //根据bounds 计算中心点
    CGPoint center;
    center.x = bounds.origin.x + bounds.size.width / 2.0;
    center.y = bounds.origin.y + bounds.size.height/ 2.0;
    
    //根据视图宽和高 中的较小值计算圆形的半径
//    float radius = (MIN(bounds.size.width, bounds.size.height)) / 2.0;
    
    //使最外层圆形成为视图的外接圆
    float maxRadius = hypot(bounds.size.width, bounds.size.height)/2.0;
    
    //该对象用于绘制直线或曲线，从而组成各种形状。
    UIBezierPath *path = [[UIBezierPath alloc]init];
    //以中心点为圆心，radius 的值为半径，定义一个0 到m_PI *2.0弧度的路径(整圆)
//    [path addArcWithCenter:center
//                    radius:radius
//                startAngle:0.0
//                  endAngle:M_PI * 2.0
//                 clockwise:YES];
    
    for(float currentRadius = maxRadius; currentRadius >0; currentRadius -= 20)
    {
     //原始的同心圆会产生一个绘制时出现的笔迹，需要将它移除
        [path moveToPoint:(CGPoint){center.x + currentRadius,center.y}];
        [path addArcWithCenter:center
                        radius:currentRadius
                    startAngle:0.0
                      endAngle:M_PI*2.0
                     clockwise:YES];
    }
    
    //设置线条宽度为10点
    path.lineWidth = 10;
    
    //设置绘制颜色为浅灰色
    [[UIColor redColor] setStroke];
    
    [path stroke];
}