Javascript snippet to aspect fit bounds in bounds.

aspect_fit_bounds_in_bounds.js

aspectFitBoundsInBounds(src, dest, center=true) {
	let WIDTH_KEY = "width";
	let HEIGHT_KEY = "height";

	let largerSide = src.height > src.width ? HEIGHT_KEY : WIDTH_KEY;
	let smallerSide = largerSide == HEIGHT_KEY ? WIDTH_KEY : HEIGHT_KEY;
	let aspectRatio = src[smallerSide]/src[largerSide];

	src[largerSide] = dest[largerSide];
	src[smallerSide] = dest[largerSide]*aspectRatio;

	src.x = dest.x;
	src.y = dest.y;
	if (center) {
		src.x += (dest.width-src.width)/2;
		src.y += (dest.height-src.height)/2;
	}
}