ios - CGRect 裁剪图像显示错误值

Question

当我尝试裁剪图像的底部时，结果从左上角放大。没有裁剪，图像显示得很好。我真的看不出我在裁剪功能上做错了什么。为什么这不返回带有裁剪的完整图像？请参阅下面的代码和结果:

- (UIImage *)croppedImageFromScreenShot
{
    // Prepare view for screen capture

    // Screen Capture

    CGRect fullScreenRect = self.view.bounds;

    UIGraphicsBeginImageContextWithOptions(fullScreenRect.size, NO, [UIScreen mainScreen].scale);

    [self.view drawViewHierarchyInRect:fullScreenRect afterScreenUpdates:YES];

    UIImage *screenShotImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    // Crop Image

    CGFloat cropDistance = 20.0;

    CGSize imageSize = screenShotImage.size;

    CGRect imageRect = CGRectMake(0.0, 0.0, imageSize.width, imageSize.height);

    CGRect cropRect = CGRectInset(imageRect, 0.0, cropDistance);

    CGImageRef imageRef = CGImageCreateWithImageInRect([screenShotImage CGImage], cropRect);

    UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];

    CGImageRelease(imageRef);

    // Restore view after screen capture


    return croppedImage;
}

裁剪效果不错，但图像放大变小了:

在没有裁剪的情况下，从下面的代码中大小就可以了:

- (UIImage *)croppedImageFromScreenShot
{
    // Prepare view for screen capture

    // Screen Capture

    CGRect fullScreenRect = self.view.bounds;

    UIGraphicsBeginImageContextWithOptions(fullScreenRect.size, NO, [UIScreen mainScreen].scale);

    [self.view drawViewHierarchyInRect:fullScreenRect afterScreenUpdates:YES];

    UIImage *screenShotImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();


    return screenShotImage;
}

返回原始图像，因为它也应该使用裁剪功能:

Answer 1

改变这个:

CGRect cropRect = CGRectInset(imageRect, 0.0, cropDistance);

进入:

CGRect cropRect = CGRectMake(0,0,imageSize.width, imageSize.height - cropDistance);

你只想定义你想要的特定矩形作为图像的子集，所以如果你想裁剪底部，那么你只需从高度中减去。