SizeProportional.swift

func size(_ imageSize: CGSize, constrainedToSize maxSize: CGSize) -> CGSize {
	if maxSize.width > 0 && maxSize.height > 0 && (maxSize.width < imageSize.width || maxSize.height < imageSize.height)
	{
		let constrainedSize: CGSize
		
		let constrainedHeight = min(imageSize.height, maxSize.height)
		let scaleProportionalToHeight = constrainedHeight / imageSize.height
		let sizeProportionalToHeight = CGSize(width: round(imageSize.width * scaleProportionalToHeight), height: constrainedHeight)
		
		let constrainedWidth = min(imageSize.width, maxSize.width)
		let scaleProportionalToWidth = constrainedWidth / imageSize.width
		let sizeProportionalToWidth = CGSize(width: constrainedWidth, height: round(imageSize.height * scaleProportionalToWidth))
		
		if (scaleProportionalToWidth > scaleProportionalToHeight)
		{
			if sizeProportionalToWidth.height > maxSize.height {
				constrainedSize = sizeProportionalToHeight
			} else {
				constrainedSize = sizeProportionalToWidth
			}
		}
		else
		{
			if sizeProportionalToHeight.width > maxSize.width {
				constrainedSize = sizeProportionalToWidth
			} else {
				constrainedSize = sizeProportionalToHeight
			}
		}

		return constrainedSize
	}
	return imageSize
}