macOS中的UIGraphicsBeginImageContextWithOptions模拟 [英] UIGraphicsBeginImageContextWithOptions analog in macOS

问题描述

这是我用来在iOS中缩放图像的代码，即将500x500图像缩放到100x100图像，然后存储缩放后的副本:

Here is the code that I'm using to scale images in iOS i.e. scale 500x500 image to 100x100 image and then store scaled copy:

+ (UIImage *)image:(UIImage *)originalImage scaledToSize:(CGSize)desiredSize {
    UIGraphicsBeginImageContextWithOptions(desiredSize, YES, [UIScreen mainScreen].scale);
    [originalImage drawInRect:CGRectMake(0, 0, desiredSize.width, desiredSize.height)];
    UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext;

    return finalImage;
}

现在，我需要在macOS应用中实现相同的功能.我怎样才能做到这一点?我看到了这样的问题，但我仍然不明白在macOS中执行此操作的逻辑.

Now I need to implement the same functionality in my macOS app. How can I do that? I saw the question like this but I still can't understand the logic of doing this in macOS.

推荐答案

经过一番搜索，我在 Swift 中发现了一个类似我的问题.所以我将其翻译成 Objective-C ，就是这样:

After some search I found a question like mine but in Swift. So I translated it in Objective-C and that's it:

+ (NSImage *)image:(NSImage *)originalImage scaledToSize:(NSSize)desiredSize {
    NSImage *newImage = [[NSImage alloc] initWithSize:desiredSize];

    [newImage lockFocus];
    [originalImage drawInRect:NSMakeRect(0, 0, desiredSize.width, desiredSize.height) fromRect:NSMakeRect(0, 0, imageWidth, imageHeight) operation:NSCompositingOperationSourceOver fraction:1];
    [newImage unlockFocus];

    newImage.size = desiredSize;
    return [[NSImage alloc] initWithData:[newImage TIFFRepresentation]];
}

但是仍然存在一个问题:如果 desiredSize = NSMakeSize(50,50); ，它将返回50 x 50像素.我猜应该是屏幕尺寸的东西.我翻译了 Swift 代码:

But there's still an issue: if desiredSize = NSMakeSize(50,50); it will return 50 by 50 pixels. It's should be something with screen scale i guess. There is Swift code that I translated:

• 示例1
• 示例2

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