半透明帮助页效果图

写了一个简单的demo
详细代码如下

- (void)viewDidLoad {
    [super viewDidLoad];
    //
    [self setupShapLayer];
}

- (void)setupShapLayer {
    // 1.创建一个遮罩View,并添加
    UIView *maskView = [[UIView alloc] initWithFrame:self.view.bounds];
    maskView.backgroundColor = [UIColor blackColor];
    maskView.alpha = 0.6;
    [self.view addSubview:maskView];
    
    // 2.贝塞尔曲线 创建一个和 遮罩View 一样大小的 第一个 backgroudPath,并添加
    UIBezierPath *backgroudPath = [UIBezierPath bezierPathWithRect:self.view.bounds];
    // 贝塞尔曲线 创建第二个小矩形的 rectPath
    CGFloat width = 160;
    CGFloat height = 100;
    CGFloat x = (self.view.bounds.size.width - width) * 0.5;
    CGFloat y = 184;
    UIBezierPath *rectPath = [UIBezierPath bezierPathWithRoundedRect:CGRectMake(x, y, width, height) cornerRadius:10];
    // rectPath 反转成矩形框以外的path
    rectPath = [rectPath bezierPathByReversingPath];
    // rectPath 
    rectPath.usesEvenOddFillRule = YES;
    // 3.
    [backgroudPath appendPath:rectPath];
    
    // 4.创建一个CAShapeLayer 图层
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.path = backgroudPath.CGPath;
    shapeLayer.fillColor = [UIColor yellowColor].CGColor; // 除了clearColor外任意颜色
    shapeLayer.lineWidth = 10;
    shapeLayer.borderColor = [UIColor redColor].CGColor;
    shapeLayer.borderWidth = 20;
    //添加图层蒙板
    maskView.layer.mask = shapeLayer;
}

然后在modal出来的视图的背景色为clearColor,再添加其它视图,注意view的层级就行了