Crop NSImage (macOS) Square without distorting - swift

Question

I am using the code below to resize an image in Swift on macOS. This is working but if the image is not square to begin with, the resizing squashes the image.
How can I resize the image but draw it in the center and keeping the ratio, preventing the squashing if the image is not square to begin with?
func resize(image: NSImage, w: CGFloat, h: CGFloat) -> NSImage {
var destSize = NSMakeSize(CGFloat(w), CGFloat(h))
var newImage = NSImage(size: destSize)
newImage.lockFocus()
image.draw(in: NSMakeRect(0, 0, destSize.width, destSize.height), from: NSMakeRect(0, 0, image.size.width, image.size.height), operation: NSCompositingOperation.sourceOver, fraction: CGFloat(1))
newImage.unlockFocus()
newImage.size = destSize
return NSImage(data: newImage.tiffRepresentation!)!
}
Thank you

Answer 1

The following line of code is the problem:
image.draw(in: NSMakeRect(0, 0, destSize.width, destSize.height), from: NSMakeRect(0, 0, image.size.width, image.size.height), operation: NSCompositingOperation.sourceOver, fraction: CGFloat(1))
You are drawing from the whole rectangle of the source into the whole rectangle of the destination. This will therefore scale the image to fit the destination, whereas you want to maintain aspect ratio. You need to decide how you want the final image to appear and adjust the source or destination rectangles accordingly.
For example, if you want to scale the result so that the whole image appears, you need to adjust either the width or height of the destination rectangle so they're in the same aspect ratio as the source.
Alternatively, if you want to crop the result, you need to adjust the width or height of the source rectangle, once again maintaining the same aspect ratio. You will also have to adjust the origin of the source rectangle if you want to crop (for example) the top and bottom.
Some of the other functions like draw(in:from:operation:fraction:) handle scaling for you, so depending on your needs, they may be better.

Answer 2

Assuming that you want to fit the entire source image into the destination image space(or size), maintaining the aspect ratio of the original image and adding some white space where the image doesn't fit into the destination.
There are three situations to consider.
The aspect ratio of the source and destination are the same.
No problem, just resize.
The aspect ratio destination is wider than the source
Height is the driving value (because it is smaller).
Figure out the height ratio from source to destination.
Use that ratio to calculate the destination width from the source width.
The aspect ratio destination is taller than the source
Width is the driving value.
Figure out the width ratio from source to destination.
Use that ratio to calculate the destination height from the source height.
I created this function to calculate the size you need.
func calcNewSize(source: NSSize, destination: NSSize) -> NSSize {
let widthRatio: Float = Float(destination.width) / Float(source.width)
let heightRatio: Float = Float(destination.height) / Float(source.height)
var newSize = NSSize()
print("widthRatio \(widthRatio) heightRatio \(heightRatio)")
if widthRatio == heightRatio {
print("use same ratio")
newSize = destination
}
else if widthRatio > heightRatio {
print("use height ratio")
newSize.height = source.height * CGFloat(heightRatio)
newSize.width = source.width * CGFloat(heightRatio)
}
else {
print("use width ratio")
newSize.height = source.height * CGFloat(widthRatio)
newSize.width = source.width * CGFloat(widthRatio)
}
return newSize
}