Core Graphics / Quartz 2D图像调整大小崩溃

Question

任务是调整图像大小。

我读过this post并采用了CGBitmapContextCreate和CGContextDrawImage方法。这就是我的调整大小功能的样子：

extension UIImage {

    func with(maxHeight: CGFloat, maxWidth: CGFloat) -> UIImage? {
        guard let image = self.cgImage else {
            return nil
        }
        var height = CGFloat(image.height)
        var width = CGFloat(image.width)
        guard height > 0 && width > 0 else {
            return nil
        }
        let maxHeight = round(maxHeight)
        let maxWidth = round(maxWidth)
        guard height > maxHeight || width > maxWidth else {
            return nil
        }
        let heightProportions = height / maxHeight
        let widthProportions = width / maxWidth
        height = heightProportions > widthProportions ? maxHeight : round(height / widthProportions)
        width = widthProportions > heightProportions ? maxWidth : round(width / heightProportions)
        let size = CGSize(width: width, height: height)
        let bitmapInfo = image.bitmapInfo.rawValue
        let bitsPerComponent = image.bitsPerComponent
        let bytesPerRow = image.bytesPerRow
        let space = image.colorSpace ?? CGColorSpaceCreateDeviceRGB()
        let context = CGContext(data: nil, width: Int(width), height: Int(height), bitsPerComponent: bitsPerComponent, bytesPerRow: bytesPerRow, space: space, bitmapInfo: bitmapInfo)
        context?.interpolationQuality = .high
        context?.draw(image, in: CGRect.init(origin: .zero, size: size))
        guard let newImage = context?.makeImage() else {
            return nil
        }
        return UIImage(cgImage: newImage)
    }
}

这个功能在测试期间确实运行良好，但我在生产线上遇到了崩溃：

context?.draw(image, in: CGRect.init(origin: .zero, size: size))

堆栈跟踪：

#11. Crashed: com.apple.root.utility-qos
0  CoreGraphics                   0x184d9a59c ERROR_CGDataProvider_BufferIsNotReadable + 12
1  CoreGraphics                   0x184d9a2c0 CGDataProviderRetainBytePtr + 216
2  CoreGraphics                   0x184e8d06c get_image_pointer + 64
3  CoreGraphics                   0x184e8d2c8 img_raw_access + 52
4  CoreGraphics                   0x184e88000 img_interpolate_read + 708
5  CoreGraphics                   0x184e8c14c img_data_lock + 7048
6  CoreGraphics                   0x184e8a56c CGSImageDataLock + 184
7  CoreGraphics                   0x184caa628 ripc_AcquireRIPImageData + 308
8  CoreGraphics                   0x184e9f1b0 ripc_DrawImage + 644
9  CoreGraphics                   0x184e8efac CGContextDrawImageWithOptions + 632
10 libswiftCoreGraphics.dylib     0x104781638 (Missing)

所以，我有两个问题：

1. 我该怎么做才能重现崩溃情况并解决问题？
2. 有没有其他方法来获得高质量的重新调整大小的图像？

Answer 1

我使用这个更简单的扩展来包装UIImage的draw(in:)。我发现它质量很高，速度也相当快。

extension UIImage {

    public func resized(maxSize: CGSize) -> UIImage? {
        let imageSize = self.size
        guard imageSize.height > 0, imageSize.width > 0 else { return nil }

        let ratio = min(maxSize.width/imageSize.width, maxSize.height/imageSize.height)
        let newSize = CGSize(width: imageSize.width*ratio, height: imageSize.height*ratio)

        let renderer = UIGraphicsImageRenderer(size: newSize)
        return renderer.image(actions: { (ctx) in
            self.draw(in: CGRect(origin: .zero, size: newSize))
        })
    }
}

用法：

let resizedImage = myImage.resized(maxSize: CGSize(width: maxWidth, height: maxHeight))

请注意，此处的大小以磅为单位进行测量，这意味着基础像素数将自动乘以设备的比例因子（例如视网膜显示的2倍）。换句话说，此方法适用于将在屏幕上显示生成的UIImage的情况。