任务是调整图像大小。
我已经阅读了这篇文章,并采用了CGBitmapContextCreate和CGContextDrawImage方法。这就是我的大小调整函数的样子:
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)
}
}
这个函数在测试期间确实运行良好,但我在生产线上遇到了生产崩溃:
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:
- 我应该怎么做才能重现崩溃情况并解决问题?
- 有没有其他方法可以获得高质量的调整大小的图像?
我使用这个更简单的扩展来包装UIImage的draw(in:)
。我发现它的质量很高,而且速度相当快。
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,这意味着基础像素数将自动乘以设备的比例因子(例如,视网膜显示器为 2 倍(。换句话说,此方法设计用于生成的 UIImage 将显示在屏幕上的情况。