iOS圆形渐变(聚光灯效果实现）

来源 https://www.jianshu.com/p/1d6a76a3d94b

• (instancetype)initWithFrame:(CGRect)frame { if (self = [super initWithFrame:frame]) { self.backgroundColor = [UIColor whiteColor]; } return self; }

• (void)drawRect:(CGRect)rect { [self draw]; }

• (void)draw {

  // 创建色彩空间对象 CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB(); // 创建起点和终点颜色分量的数组 CGFloat colors[] = { 1, 0, 0, 1.00,//start color(r,g,b,alpha) 255, 255, 255, 1.00,//end color };

  //形成梯形，渐变的效果 CGGradientRef gradient = CGGradientCreateWithColorComponents (rgb, colors, NULL, 2);

// NSLog(@”%lu”,sizeof(colors)/(sizeof(colors[0])*4));

// 起点颜色起始圆心
CGPoint start = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);
// 终点颜色起始圆心
CGPoint end = CGPointMake(self.frame.size.width/2, self.frame.size.height/2);
// 起点颜色圆形半径
CGFloat startRadius = 0.0f;
// 终点颜色圆形半径
CGFloat endRadius = 100;
// 获取上下文
CGContextRef graCtx = UIGraphicsGetCurrentContext();
// 创建一个径向渐变
CGContextDrawRadialGradient(graCtx, gradient, start, startRadius, end, endRadius, 0);

//releas
CGGradientRelease(gradient);
gradient=NULL;
CGColorSpaceRelease(rgb); }