Cocoa 怎样使NSImageView的图片正确的满屏放大缩小

NSImage *newImg = [self resizeImage:sourceImage size:newSize];
[aNSImageView setImage:newImg];

/**
 Resize the image to fit the new size, keeping the aspect ration constant
 If the image is smaller than the new size, it is scaled up and filled the new frame
 If the image is larger than the new size, it is downsized, and filled the new frame
 - SHAGRU.COM -
 */
- (NSImage*) resizeImage:(NSImage*)sourceImage size:(NSSize)size{
    
    NSRect targetFrame = NSMakeRect(0, 0, size.width, size.height);
    NSImage*  targetImage = [[NSImage alloc] initWithSize:size];
    
    NSSize sourceSize = [sourceImage size];
    
    float ratioH = size.height/ sourceSize.height;
    float ratioW = size.width / sourceSize.width;
    
    NSRect cropRect = NSZeroRect;
    
    if (ratioH >= ratioW) {
        cropRect.size.width = floor (size.width / ratioH);
        cropRect.size.height = sourceSize.height;
    } else {
        cropRect.size.width = sourceSize.width;
        cropRect.size.height = floor(size.height / ratioW);
    }
    
    cropRect.origin.x = floor( (sourceSize.width - cropRect.size.width)/2 );
    cropRect.origin.y = floor( (sourceSize.height - cropRect.size.height)/2 );
    
    
    [targetImage lockFocus];
    
    [sourceImage drawInRect:targetFrame
                   fromRect:cropRect       //portion of source image to draw
                  operation:NSCompositeCopy  //compositing operation
                   fraction:1.0              //alpha (transparency) value
             respectFlipped:YES              //coordinate system
                      hints:@{NSImageHintInterpolation:
                                  [NSNumber numberWithInt:NSImageInterpolationLow]}];
    
    [targetImage unlockFocus];
    
    return targetImage;
}

参考自：https://blog.csdn.net/shagru/article/details/9779183