获取 Image 的 UIBezierPath 没有透明区域

问：

我有一个透明的图像，形状是这样的。我们可以提取这张图片吗？例如，我可以在课堂上自己画一个六边形，但我无法得到这个形状。UIBezierPathUIViewUIBezierPath

原始图像：

class FreeShapeView: UIView {
    override func draw(_ rect: CGRect) {
        let context = UIGraphicsGetCurrentContext()
        context?.clear(rect)
      
        context?.setAllowsAntialiasing(true)
        context?.setShouldAntialias(true)
        context?.setLineJoin(CGLineJoin.round)
        
        let edge: CGFloat = 5.9/2

        let path: UIBezierPath = UIBezierPath()
        
        path.move(to: CGPoint(x: rect.width/2, y: edge))
        path.addLine(to: CGPoint(x: rect.width - edge, y: rect.height/3))
        path.addLine(to: CGPoint(x: rect.width - edge, y: rect.height/3*2))
        path.addLine(to: CGPoint(x: rect.width/2, y: rect.height - edge))
        path.addLine(to: CGPoint(x: edge, y: rect.height/3*2))
        path.addLine(to: CGPoint(x: edge, y: rect.height/3))
        
        path.close()
        context?.addPath(path.cgPath)
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .clear
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        backgroundColor = .clear
    }
}

我的 OpenCV 目标 C 代码

      + (UIBezierPath *)removeTransparentAreaAndFindContours:(UIImage *)image {
    // Convert UIImage to cv::Mat
   
    cv::Mat cvImage = [self cvMatFromUIImage:image];


    // Convert image to grayscale
    cv::Mat grayscaleImage;
    cv::cvtColor(cvImage, grayscaleImage, cv::COLOR_RGBA2GRAY);

    // Apply threshold to create binary image
    cv::Mat binaryImage;
    cv::threshold(grayscaleImage, binaryImage, 1, 255, cv::THRESH_BINARY);

    // Find contours
    std::vector<std::vector<cv::Point>> contours;
    std::vector<cv::Vec4i> hierarchy;
    cv::findContours(binaryImage, contours, hierarchy, cv::RETR_EXTERNAL, cv::CHAIN_APPROX_SIMPLE);

    // Create a UIBezierPath from the contours
    UIBezierPath *bezierPath = [UIBezierPath bezierPath];
    for (size_t i = 0; i < contours.size(); i++) {
        const std::vector<cv::Point> &contour = contours[i];
        for (size_t j = 0; j < contour.size(); j++) {
            const cv::Point &point = contour[j];
            CGPoint cgPoint = CGPointMake(point.x, point.y);
            if (j == 0) {
                [bezierPath moveToPoint:cgPoint];
            } else {
                [bezierPath addLineToPoint:cgPoint];
            }
        }
        [bezierPath closePath];
    }

    return bezierPath;
}

+ (cv::Mat)cvMatFromUIImage:(UIImage *)image {
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
    CGFloat cols = image.size.width;
    CGFloat rows = image.size.height;
    cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per channel, 4 channels (RGBA)

    CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, cols, rows, 8, cvMat.step[0], colorSpace, kCGImageAlphaNoneSkipLast | kCGBitmapByteOrderDefault);
    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
    CGContextRelease(contextRef);

    return cvMat;
}

我得到了这样的结果.

Element 1: Type = MoveToPoint, Points = (0.0, 0.0) (6.9370081173396e-310, 0.0) 
Element 2: Type = AddLineToPoint, Points = (0.0, 794.0) (6.9370081173396e-310, 0.0) 
Element 3: Type = AddLineToPoint, Points = (619.0, 794.0) (6.9370081173396e-310, 0.0) 
Element 4: Type = AddLineToPoint, Points = (620.0, 795.0) (6.9370081173396e-310, 0.0) 
Element 5: Type = AddLineToPoint, Points = (620.0, 1270.0) (6.9370081173396e-310, 0.0) 
Element 6: Type = AddLineToPoint, Points = (1998.0, 1270.0) (6.9370081173396e-310, 0.0) 
Element 7: Type = AddLineToPoint, Points = (1998.0, 0.0) (6.9370081173396e-310, 0.0) 
Element 8: Type = CloseSubpath, Points = (1998.0, 0.0) (6.9370081173396e-310, 0.0) 

测试代码为：

 path = UIBezierPath()
        
        path.move(to: CGPoint(x: 0.0, y: 0.0))
        path.addLine(to: CGPoint(x:0.0 , y:794.0 ))
        path.addLine(to: CGPoint(x:619.0 , y:794.0 ))
        path.addLine(to: CGPoint(x: 620.0, y: 795.0 ))
        path.addLine(to: CGPoint(x:620.0 , y:1270.0 ))
        path.addLine(to: CGPoint(x: 1998.0, y:1270.0 ))
        path.addLine(to: CGPoint(x:1998.0 , y: 0.0))
        
        path.close()
        context?.addPath(path.cgPath)

但它是这样画的：

我做错了什么？谢谢