将 UIImage 剪辑到 UIBezierPath（不屏蔽）

Question

我正在尝试根据给定的UIBezierPath 剪裁UIImage，但生成的图像保留了原始形状和大小。我希望形状和大小类似于路径，即新图像的可见内容。

看看下面这个例子：

以下是我用来屏蔽给定路径的图像的代码：

func imageByApplyingClippingBezierPath(_ path: UIBezierPath) -> UIImage {
    UIGraphicsBeginImageContextWithOptions(CGSize(
        width: size.width,
        height: size.height
    ), false, 0.0)
    let context = UIGraphicsGetCurrentContext()!
    context.saveGState()

    path.addClip()
    draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))

    let newImage = UIGraphicsGetImageFromCurrentImageContext()!

    context.restoreGState()
    UIGraphicsEndImageContext()

    return newImage
}

一种解决方案是在遮盖图像后对其进行裁剪，但理想情况下，我希望一次性尽可能简单有效地完成此操作。

任何解决方案/提示将不胜感激。

Answer 1

感谢Rob，我能够使用CGImage 的cropping(to:) 方法实现解决方案。

这是一个两步过程，首先我使用给定的路径屏蔽图像，然后使用路径的边界裁剪结果。

以下是我实现剪辑UIBezierPathUIImage扩展的最终工作源代码：

extension UIImage {

    func imageByApplyingClippingBezierPath(_ path: UIBezierPath) -> UIImage {
        // Mask image using path
        let maskedImage = imageByApplyingMaskingBezierPath(path)

        // Crop image to frame of path
        let croppedImage = UIImage(cgImage: maskedImage.cgImage!.cropping(to: path.bounds)!)
        return croppedImage
    }

    func imageByApplyingMaskingBezierPath(_ path: UIBezierPath) -> UIImage {
        // Define graphic context (canvas) to paint on
        UIGraphicsBeginImageContext(size)
        let context = UIGraphicsGetCurrentContext()!
        context.saveGState()

        // Set the clipping mask
        path.addClip()
        draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))

        let maskedImage = UIGraphicsGetImageFromCurrentImageContext()!

        // Restore previous drawing context
        context.restoreGState()
        UIGraphicsEndImageContext()

        return maskedImage
    }

}

Answer 2

我在目标 C 中使用以下内容，将任何图像裁剪为非透明矩形。检查它是否有用

@implementation UIImage (cropTransperant)
- (UIImage *) CropimageByTrimmingTransparentPixels {
    int rows = self.size.height;
    int cols = self.size.width;
    int bytesPerRow = cols*sizeof(uint8_t);

    if ( rows < 2 || cols < 2 ) {
        return self;
    }


    uint8_t *bitmapData = calloc(rows*cols, sizeof(uint8_t));


    CGContextRef contextRef = CGBitmapContextCreate(bitmapData, cols, rows, 8, bytesPerRow, NULL, kCGImageAlphaOnly);


    CGImageRef cgImage = self.CGImage;
    CGRect rect = CGRectMake(0, 0, cols, rows);
    CGContextDrawImage(contextRef, rect, cgImage);

    //get all non-transparent pixels in every row and every column
    uint16_t *rowSum = calloc(rows, sizeof(uint16_t));
    uint16_t *colSum = calloc(cols, sizeof(uint16_t));

    //loop through all pixels
    for ( int row = 0; row < rows; row++) {
        for ( int col = 0; col < cols; col++)
        {
            if ( bitmapData[row*bytesPerRow + col] ) {  //when you get non transperant pixel
                rowSum[row]++;
                colSum[col]++;
            }
        }
    }

       UIEdgeInsets crop = UIEdgeInsetsMake(0, 0, 0, 0); //croprect, initialize with 0,0,0,

    for ( int i = 0; i<rows; i++ ) {        //get top
        if ( rowSum[i] > 0 ) {
            crop.top = i; break;
        }
    }

    for ( int i = rows; i >= 0; i-- ) {     //get bottom
        if ( rowSum[i] > 0 ) {
            crop.bottom = MAX(0, rows-i-1); break;
        }
    }

    for ( int i = 0; i<cols; i++ ) {        //get left
        if ( colSum[i] > 0 ) {
            crop.left = i; break;
        }
    }

    for ( int i = cols; i >= 0; i-- ) {     //get right
        if ( colSum[i] > 0 ) {
            crop.right = MAX(0, cols-i-1); break;
        }
    }

    free(bitmapData);
    free(colSum);
    free(rowSum);

    if ( crop.top == 0 && crop.bottom == 0 && crop.left == 0 && crop.right == 0 ) {

        return self;
    }
    else {

        rect.origin.x += crop.left;
        rect.origin.y += crop.top;
        rect.size.width -= crop.left + crop.right;
        rect.size.height -= crop.top + crop.bottom;

        //crop  image to calcualted rect
        CGImageRef newImage = CGImageCreateWithImageInRect(cgImage, rect);


        return [UIImage imageWithCGImage:newImage];
    }
}

@end