正确裁剪和缩放UIImage

Question

我正在尝试将图像裁剪成正方形，然后将其缩放到200x200大小。这是我使用的代码，但它对我来说并不适用。我得到的图像有时方向不同，或者没有从中心裁剪，或者比它应该的更宽。

float scale = _avatar.image.scale;
UIImageOrientation orientation = _avatar.image.imageOrientation;
if(_avatar.image.size.width < _avatar.image.size.height){ // avatar is a UIImageView
    float startingY = (_avatar.image.size.height-_avatar.image.size.width)/2; // image is taller, determine the origin of the width-sized square, which will be the new image
    CGImageRef imageRef = CGImageCreateWithImageInRect([_avatar.image CGImage], CGRectMake(0, startingY, _avatar.image.size.width, _avatar.image.size.width));
    _avatar.image = [UIImage imageWithCGImage:imageRef scale:scale orientation:orientation];
    CGImageRelease(imageRef);
} else {
    float startingX = (_avatar.image.size.width-_avatar.image.size.height)/2; // image is wider, determine the origin of the height-sized square, which will be the new image
    CGImageRef imageRef = CGImageCreateWithImageInRect([_avatar.image CGImage], CGRectMake(startingX, 0, _avatar.image.size.height, _avatar.image.size.height));
    _avatar.image = [UIImage imageWithCGImage:imageRef scale:scale orientation:orientation];
    CGImageRelease(imageRef);
}
UIGraphicsBeginImageContextWithOptions(CGSizeMake(200, 200), YES, 0.0);
[_avatar.image drawInRect:CGRectMake(0, 0, 200, 200)];
UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

必须如何才能达到正确的结果？

Answer 1

我建议您将这个类别用于发布在github上的UIImage。它们也是非常简单的课程，你也可以用它们来学习引擎盖下的东西。

Answer 2

UIImage已经为您完成了所有的坐标和方向技巧。因此，您不应该使用UIImage对象的宽度和高度来计算正方形的坐标。您可以利用UIKit来裁剪图像。

CGFloat startingX = 0;
CGFloat startingY = 0;
CGFloat squareWidth;
if(_avatar.image.size.width < _avatar.image.size.height){ // avatar is a UIImageView  
    startingY = (_avatar.image.size.height-_avatar.image.size.width)/2; // image is taller, determine the origin of the width-sized square, which will be the new image  
    squareWidth = _avatar.image.size.width;
} else {
    startingX = (_avatar.image.size.width-_avatar.image.size.height)/2; // image is wider, determine the origin of the height-sized square, which will be the new image
    squareWidth = _avatar.image.size.height;
}  
UIGraphicsBeginImageContextWithOptions(CGSizeMake(squareWidth, squareWidth), YES, 0.0);
[_avatar.image drawAtPoint:CGPointMake(-startingX, -startingY)]; // Make an offset to draw part of the image
UIImage *croppedImage = UIGraphicsGetImageFromCurrentImageContext();  
UIGraphicsEndImageContext();
UIGraphicsBeginImageContextWithOptions(CGSizeMake(200, 200), YES, 0.0);
[croppedImage  drawInRect:CGRectMake(0, 0, 200, 200)];
UIImage *scaledImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();