Resizing an Image by preserving aspect ratio in swift - swift

Question

I have the following extension to resize an image.
extension NSImage {
func resizeImage(width: CGFloat, _ height: CGFloat) -> NSImage {
let img = NSImage(size: CGSize(width:width, height:height))
img.lockFocus()
let ctx = NSGraphicsContext.current()
ctx?.imageInterpolation = .high
self.draw(in: NSMakeRect(0, 0, width, height), from: NSMakeRect(0, 0, size.width, size.height), operation: .copy, fraction: 1)
img.unlockFocus()
return img
}
}
On resizing the aspect ratio is not preserved.
How can I modify the code to preserve aspect ratio?
Please advice.
Update:
This the logic used in C# .I don't know how to do this in swift.
double ratioX = (double) canvasWidth / (double) originalWidth;
double ratioY = (double) canvasHeight / (double) originalHeight;
// use whichever multiplier is smaller
double ratio = ratioX < ratioY ? ratioX : ratioY;
// now we can get the new height and width
int newHeight = Convert.ToInt32(originalHeight * ratio);
int newWidth = Convert.ToInt32(originalWidth * ratio);
// Now calculate the X,Y position of the upper-left corner
// (one of these will always be zero)
int posX = Convert.ToInt32((canvasWidth - (originalWidth * ratio)) / 2);
int posY = Convert.ToInt32((canvasHeight - (originalHeight * ratio)) / 2);

Answer 1

You can change your method signature to make it scale your image using a percentage instead of a size:
extension NSImage {
func resizedTo(width: CGFloat, height: CGFloat) -> NSImage {
let ratioX = width / size.width
let ratioY = height / size.height
let ratio = ratioX < ratioY ? ratioX : ratioY
let canvasSize = NSSize(width: size.width * ratio, height: size.height * ratio)
let img = NSImage(size: canvasSize)
img.lockFocus()
NSGraphicsContext.current?.imageInterpolation = .high
draw(in: NSRect(origin: CGPoint(x: (canvasSize.width - (size.width * ratio)) / 2, y: (canvasSize.height - (size.height * ratio)) / 2), size: canvasSize), from: NSRect(origin: .zero, size: size), operation: .copy, fraction: 1)
img.unlockFocus()
return img
}
func resizedTo(percentage: CGFloat) -> NSImage {
let canvasSize = CGSize(width: size.width * percentage, height: size.height * percentage)
let img = NSImage(size: canvasSize)
img.lockFocus()
NSGraphicsContext.current?.imageInterpolation = .high
draw(in: NSRect(origin: .zero, size: canvasSize), from: NSRect(origin: .zero, size: size), operation: .copy, fraction: 1)
img.unlockFocus()
return img
}
func resizedTo(width: CGFloat) -> NSImage {
let canvasSize = CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))
let img = NSImage(size: canvasSize)
img.lockFocus()
NSGraphicsContext.current?.imageInterpolation = .high
draw(in: NSRect(origin: .zero, size: canvasSize), from: NSRect(origin: .zero, size: size), operation: .copy, fraction: 1)
img.unlockFocus()
return img
}
}