xcode iPhone：如何绘制一幅图像
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/2670733/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
iPhone: How can you draw a piece of an image
提问by Mark
Code sample
代码示例
- (void)drawRect:(CGRect)rect {
[super drawRect:rect];
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSaveGState(context);
CGContextTranslateCTM(context, 0, self.frame.size.height);
CGContextScaleCTM(context, 1.0, -1.0);
CGContextDrawImage(context, CGRectMake(0.0, 0.0, self.frame.size.width, self.frame.size.height), [UIImage imageNamed:@"sample.png"].CGImage);
CGContextRestoreGState(context);
}
================
================
I would like to copy a certain rect within an image to the context, so not the entire image is drawn but just a piece of the image. Does anyone have a solution for this? I can't find anything on google nor the documentation.
我想将图像中的某个矩形复制到上下文中，因此不会绘制整个图像而只是图像的一部分。有没有人对此有解决方案？我在谷歌和文档上都找不到任何东西。
I know there are alternatives like: 1. Create a UIView with clipping and then just position the UIImageView within it. 2. Create the UIImageView within the UIScrollView and use content offset.
我知道有一些替代方法，例如： 1. 创建一个带有剪辑的 UIView，然后将 UIImageView 放置在其中。2. 在 UIScrollView 中创建 UIImageView 并使用内容偏移。
But I think those are lame...
但是我觉得这些都是废话...
回答by James
CGImageCreateWithImageInRect should work fine. That's how I do it. Here's an example:
CGImageCreateWithImageInRect 应该可以正常工作。我就是这样做的。下面是一个例子：
CGImageRef ref = CGImageCreateWithImageInRect(some_UIImage.CGImage, CGRectMake(x, y, height, width));
UIImage *img = [UIImage imageWithCGImage:ref];
This example gets a CGImageRef from the CGImage property of another_UIImage, an instance of UIImage, then crops it, and turns it back into a UIImage with UIImage's imageWithCGImage constructor method. Good luck!
本示例从 another_UIImage 的 CGImage 属性（UIImage 的一个实例）中获取一个 CGImageRef，然后将其裁剪，并使用 UIImage 的 imageWithCGImage 构造函数将其转换回 UIImage。祝你好运！
James
詹姆士
回答by adam
You could try CGImageCreateWithImageInRect
你可以试试 CGImageCreateWithImageInRect
回答by Mark
This did work:
这确实有效：
UIGraphicsBeginImageContext(rect.size);
CGContextRef currentContext = UIGraphicsGetCurrentContext();
CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);
CGContextClipToRect( currentContext, clippedRect);
CGRect drawRect = CGRectMake(rect.origin.x * -1,
rect.origin.y * -1,
imageToCrop.size.width,
imageToCrop.size.height);
CGContextDrawImage(currentContext, drawRect, imageToCrop.CGImage);
UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
