ios - 根据 UIScrollView 内的视口(viewport)裁剪 UIImage

Question

我在 UIScrollView 中有一个 UIImageView(用 Aspect Fill 初始化)。用户应使用它来调整 UIImage 的大小和位置到他喜欢的位置，按下按钮，然后他在屏幕上看到的内容将被发送到服务器，仅在原始图像坐标中。换句话说，生成的图像会比屏幕上的图像大。

到目前为止，这是我的代码的重要部分:

// select the original 
CGFloat imageRatio = self.imageView.image.size.width / self.imageView.image.size.height;    
CGFloat viewRatio  = self.imageView.frame.size.width / self.imageView.frame.size.height;
CGFloat scale;

// get the scale factor of the image being "aspect-filled"
if(imageRatio < viewRatio) {
    scale = self.imageView.image.size.width / self.imageView.frame.size.width;
} else {
    scale = self.imageView.image.size.height / self.imageView.frame.size.height;
}

// get the cropping origin in the image's original coordinates
CGFloat originX = self.imageScrollView.contentOffset.x * scale;
CGFloat originY = self.imageScrollView.contentOffset.y * scale;
CGPoint origin = CGPointMake(originX, originY);

// get the cropping size in the image's original coordinates
CGFloat width  = self.imageView.image.size.width  / self.imageScrollView.zoomScale;
CGFloat height = self.imageView.image.size.height / self.imageScrollView.zoomScale;
CGSize size = CGSizeMake(width, height);

// create the new image from the original one
CGRect imageRect = CGRectMake(origin.x, origin.y, size.width, size.height);
struct CGImage *croppedCGImage = CGImageCreateWithImageInRect(self.imageView.image.CGImage, imageRect);

它看起来已经非常接近我想要的。原点计算至少看起来是正确的。但是，生成的图像仍然存在一些差异，我猜这是由于可能图像的纵横比不同所致。可能我需要以某种方式将 scale 添加到我的 size 方程中，但我真的无法理解如何。

希望有人能帮我把这最后两米...

[编辑]

根据第一条评论，我尝试了以下方法。但不知何故，我的 targetFrame 始终与 scrollFrame 相同。对我来说是不是太晚了才能做正确的事？？

CGFloat zoom = self.imageScrollView.zoomScale;
// the full image resolution
CGRect fullImageFrame = CGRectMake(0, 0,
                                   self.imageView.image.size.width,
                                   self.imageView.image.size.height);
UIView *fullImageView = [[[UIView alloc] initWithFrame:fullImageFrame] autorelease];
// the theoretical size of the image on the screen
CGRect previewImageFrame = CGRectMake(0, 0,
                                      self.imageView.frame.size.width * zoom,
                                      self.imageView.frame.size.height * zoom);
UIView *previewImageView = [[[UIView alloc] initWithFrame:previewImageFrame] autorelease];
// the excerpt of previewImageFrame really visible
CGRect scrollFrame = CGRectMake(self.imageScrollView.contentOffset.x,
                                self.imageScrollView.contentOffset.y,
                                self.imageScrollView.frame.size.width,
                                self.imageScrollView.frame.size.height);
// that excerpt transferred to the full resolution image's coordinates
CGRect targetFrame = [fullImageView convertRect:scrollFrame fromView:previewImageView];

Answer 1

您可能希望探索:

(CGRect)convertRect:(CGRect)rect toView:(UIView *)view

此方法和其他类似方法允许您获取 View 并根据父 View 中的位置调整其坐标系，而不是最初打算或定位的父 View 。