1. 使用 CAShapeLayer 繪制圓

UIView *bgView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
    [self.view addSubview:bgView];
    
    //創建 bezierPath
    UIBezierPath *path = [[UIBezierPath alloc] init];
    [path moveToPoint:CGPointMake(175, 100)];
    [path addArcWithCenter:CGPointMake(150, 100) radius:25 startAngle:0 endAngle:M_PI*2 clockwise:YES];
    
    //創建 shapeLayer
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.strokeColor = [UIColor redColor].CGColor;
    shapeLayer.fillColor = [UIColor clearColor].CGColor;
    shapeLayer.lineWidth = 5;
    shapeLayer.path = path.CGPath;
    
    [bgView.layer addSublayer:shapeLayer];

fillColor 用來控制圓內部的顏色

2. 繪制火柴人

火柴人.png

實現代碼如下：

UIView *bgView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
    [self.view addSubview:bgView];
    
    //創建 bezierPath
    UIBezierPath *path = [[UIBezierPath alloc] init];
    [path moveToPoint:CGPointMake(175, 100)];
    [path addArcWithCenter:CGPointMake(150, 100) radius:25 startAngle:0 endAngle:M_PI*2 clockwise:YES];
    [path moveToPoint:CGPointMake(150, 125)];
    [path addLineToPoint:CGPointMake(150, 175)];
    [path addLineToPoint:CGPointMake(125, 225)];
    [path moveToPoint:CGPointMake(150, 175)];
    [path addLineToPoint:CGPointMake(175, 225)];
    [path moveToPoint:CGPointMake(100, 150)];
    [path addLineToPoint:CGPointMake(200, 150)];
    
    //創建 shapeLayer
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.strokeColor = [UIColor redColor].CGColor;
    shapeLayer.fillColor = [UIColor clearColor].CGColor;
    shapeLayer.lineWidth = 5;
    shapeLayer.lineJoin = kCALineJoinRound;
    shapeLayer.lineCap = kCALineCapRound;
    shapeLayer.path = path.CGPath;
    
    [bgView.layer addSublayer:shapeLayer];

lineCap 用來設置繪制開始及結束時的方式，直接結束還是以圓角的方式結束。

3. 不規則的蒙版
   原圖（需要被蒙版的圖片）：

原圖.png

蒙版圖片：

蒙版圖片.png

蒙版后的結果：

蒙版后的結果.png

相關代碼：

UIView *bgView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];
    [self.view addSubview:bgView];
    
    CGRect rect = CGRectMake(50, 150, 100, 100);
    CGSize radii = CGSizeMake(20, 20);
    UIRectCorner corners = UIRectCornerTopRight | UIRectCornerBottomRight | UIRectCornerBottomLeft;
    //create path
    UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:corners cornerRadii:radii];
    
    //創建 shapeLayer
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.strokeColor = [UIColor redColor].CGColor;
    shapeLayer.fillColor = [UIColor redColor].CGColor;
    shapeLayer.lineWidth = 1;
    shapeLayer.lineJoin = kCALineJoinRound;
    shapeLayer.lineCap = kCALineCapRound;
    shapeLayer.path = bezierPath.CGPath;

    UIImageView * imageView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 200, 400, 300)];
    imageView.image = [UIImage imageNamed:@"Sprite"];
    [bgView addSubview:imageView];
    
    imageView.layer.mask = shapeLayer;

參考鏈接