单边角的反向 UIBezierPath

Question

我想创建一个蒙版路径，其最终输出将是一个带有凹面的角。

我使用-bezierPathWithRoundedRect:byRoundingCorners:cornerRadii: 方法创建了一个UIBezierPath 并指定只需要圆角（在本例中为UIRectCornerBottomLeft），我认为通过反转这个路径，我应该首先得到会被削减的东西。
为此，我正在尝试-bezierPathByReversingPath，但它似乎没有任何区别（有或没有，因为我得到的是正常的贝塞尔路径，而不是相反的）

这是我迄今为止尝试过的：

UIView *vwTest = [[UIView alloc] init];
[vwTest setFrame:CGRectMake(100.0f, 100.0f, 100.0f, 100.0f)];
[vwTest setBackgroundColor:[UIColor redColor]];
[self.view addSubview:vwTest];

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:vwTest.bounds
                                               byRoundingCorners:UIRectCornerBottomLeft
                                                     cornerRadii:CGSizeMake(50.0f, 50.0f)];

//get reverse path but doesn't seem to work as I think it should
maskPath = [maskPath bezierPathByReversingPath]; 

CAShapeLayer *maskLayer = [CAShapeLayer layer];
[maskLayer setFrame:vwTest.bounds];
[maskLayer setPath:maskPath.CGPath];

[vwTest.layer setMask:maskLayer];
[vwTest.layer setMasksToBounds:YES];
[vwTest setNeedsDisplay];

---

根据下图，我想要实现的是显示UIView 的红色部分并消除该区域的其余部分。

---

目前，我在子视图上做子视图之类的事情，并将一个子视图的颜色与主视图的背景颜色同步（很糟糕，但至少我得到了所需的输出）：

[self.view setBackgroundColor:[UIColor lightGrayColor]];

UIView *vwTest = [[UIView alloc] init];
[vwTest setFrame:CGRectMake(100.0f, 100.0f, 100.0f, 100.0f)];
[vwTest setBackgroundColor:[UIColor redColor]];
[self.view addSubview:vwTest];

UIView *vwPatch = [[UIView alloc] init];
[vwPatch setFrame:vwTest.bounds];
[vwPatch setBackgroundColor:vwTest.superview.backgroundColor];
[vwTest addSubview:vwPatch];

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:vwPatch.bounds
                                               byRoundingCorners:UIRectCornerBottomLeft
                                                     cornerRadii:CGSizeMake(50.0f, 50.0f)];
CAShapeLayer *maskLayer = [CAShapeLayer layer];
[maskLayer setFrame:vwPatch.bounds];
[maskLayer setPath:maskPath.CGPath];

[vwPatch.layer setMask:maskLayer];
[vwPatch.layer setMasksToBounds:YES];
[vwPatch setNeedsDisplay];

---

有人，请指点我正确的方向。

Answer 1

通过查看问题中的代码，我假设您希望左下角（因为您正在使用 UIRectCornerBottomLeft）是半径为 30 的凹面。您不能像所有情况一样使用 bezierPathByReversingPath它从字面上反转了路径，它还在文档中说：

反转路径并不一定会在渲染时改变路径的外观。

编辑：
现在已将图像添加到问题中，OP 想要形状的倒数：

CAShapeLayer *mask = [CAShapeLayer layer];
mask.frame = view.layer.bounds;

UIBezierPath *path = [UIBezierPath bezierPath];
CGFloat radius = 50;
CGRect rect = mask.bounds;
[path moveToPoint:CGPointMake(CGRectGetMinX(rect), CGRectGetMaxY(rect))];
[path addLineToPoint:CGPointMake(CGRectGetMinX(rect), CGRectGetMaxY(rect) - radius)];
[path addArcWithCenter:CGPointMake(CGRectGetMinX(rect) + radius, CGRectGetMaxY(rect) - radius) radius:radius startAngle:M_PI endAngle:M_PI_2 clockwise:NO];
[path closePath];

mask.path = path.CGPath;
view.layer.mask = mask;

路径的形状是问题中 OPs 图像的红色位。

---

在发布图片之前回答 - 可能会用于其他人

以下代码将产生这种形状：

CGFloat cornerRadius = 30;

CGRect rect = CGRectMake(0, 0, 200, 100);

UIBezierPath *path = [UIBezierPath bezierPath];

// Draw the complete sides
[path moveToPoint:rect.origin];
[path addLineToPoint:CGPointMake(CGRectGetMaxX(rect), CGRectGetMinY(rect))];
[path addLineToPoint:CGPointMake(CGRectGetMaxX(rect), CGRectGetMaxY(rect))];

// Stop short for the start of the arc
[path addLineToPoint:CGPointMake(CGRectGetMinX(rect) + cornerRadius, CGRectGetMaxY(rect))];

// Concave arc
[path addArcWithCenter:CGPointMake(CGRectGetMinX(rect), CGRectGetMaxY(rect)) radius:cornerRadius startAngle:0 endAngle:M_PI_2 * 3 clockwise:NO];

// Complete the path
[path closePath];

更新：有用的类别

UIBezierPath 上的类别，以便您可以选择哪些角（UIRectCorners 的位掩码）和半径。

UIBezierPath+RDHConcaveCorners.h

@interface UIBezierPath (RDHConcaveCorners)

+(instancetype)bezierPathWithRoundedRect:(CGRect)rect byConcaveRoundingCorners:(UIRectCorner)corners cornerRadius:(CGFloat)radius;

@end

UIBezierPath+RDHConcaveCorners.m

@implementation UIBezierPath (RDHConcaveCorners)

+(instancetype)bezierPathWithRoundedRect:(CGRect)rect byConcaveRoundingCorners:(UIRectCorner)corners cornerRadius:(CGFloat)cornerRadius
{
    CGFloat halfWidth = CGRectGetWidth(rect) / 2;
    CGFloat halfHeight = CGRectGetHeight(rect) / 2;
    if (cornerRadius > halfWidth || cornerRadius > halfHeight) {
        cornerRadius = MIN(halfWidth, halfHeight);
    }

    UIBezierPath *path = [self bezierPath];

    CGPoint topLeft = CGPointMake(CGRectGetMinX(rect), CGRectGetMinY(rect));
    if (corners & UIRectCornerTopLeft) {
        [path moveToPoint:CGPointMake(topLeft.x, topLeft.y + cornerRadius)];
        [path addArcWithCenter:topLeft radius:cornerRadius startAngle:M_PI_2 endAngle:0 clockwise:NO];
    } else {
        [path moveToPoint:topLeft];
    }

    CGPoint topRight = CGPointMake(CGRectGetMaxX(rect), CGRectGetMinY(rect));
    if (corners & UIRectCornerTopRight) {
        [path addLineToPoint:CGPointMake(topRight.x - cornerRadius, topRight.y)];
        [path addArcWithCenter:topRight radius:cornerRadius startAngle:M_PI endAngle:M_PI_2 clockwise:NO];
    } else {
        [path addLineToPoint:topRight];
    }

    CGPoint bottomRight = CGPointMake(CGRectGetMaxX(rect), CGRectGetMaxY(rect));
    if (corners & UIRectCornerBottomRight) {
        [path addLineToPoint:CGPointMake(bottomRight.x, bottomRight.y - cornerRadius)];
        [path addArcWithCenter:bottomRight radius:cornerRadius startAngle:M_PI_2 * 3 endAngle:M_PI clockwise:NO];

    } else {
        [path addLineToPoint:bottomRight];
    }

    CGPoint bottomLeft = CGPointMake(CGRectGetMinX(rect), CGRectGetMaxY(rect));
    if (corners & UIRectCornerBottomLeft) {
        [path addLineToPoint:CGPointMake(bottomLeft.x + cornerRadius, bottomLeft.y)];
        [path addArcWithCenter:bottomLeft radius:cornerRadius startAngle:0 endAngle:M_PI_2 * 3 clockwise:NO];
    } else {
        [path addLineToPoint:bottomLeft];
    }

    // Complete the path
    [path closePath];

    return path;
}

@end