Confused about NSImageView scaling - cocoa

Question

I'm trying to display a simple NSImageView with it's image centered without scaling it like this:
Just like iOS does when you set an UIView's contentMode = UIViewContentModeCenter
So I tried all NSImageScaling values, this is what I get when I chose NSScaleNone
I really don't understand what's going on :-/

Answer 1

You can manually generate the image of the correct size and content, and set it to be the image of the NSImageView so that NSImageView doesn't need to do anything.
NSImage *newImg = [self resizeImage:sourceImage size:newSize];
[aNSImageView setImage:newImg];
The following function resizes an image to fit the new size, keeping the aspect ratio intact. If the image is smaller than the new size, it is scaled up and filled with the new frame. If the image is larger than the new size, it is downsized, and filled with the new frame
- (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;}

Answer 2

Here's an awesome category for NSImage: NSImage+ContentMode
It allows content modes like in iOS, works great.

Answer 3

Set image scaling property to NSImageScaleAxesIndependently which will scale image to fill rectangle.This will not preserve aspect ratio.

Answer 4

Swift version of #Shagru's answer (without the hints)
func resizeImage(_ sourceImage:NSImage, size:CGSize) -> NSImage
{
let targetFrame = CGRect(origin: CGPoint.zero, size: size);
let targetImage = NSImage.init(size: size)
let sourceSize = sourceImage.size
let ratioH = size.height / sourceSize.height;
let ratioW = size.width / sourceSize.width;
var cropRect = CGRect.zero;
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.draw(in: targetFrame, from: cropRect, operation: .copy, fraction: 1.0, respectFlipped: true, hints: nil )
targetImage.unlockFocus()
return targetImage;
}