Consider making math::resize_dimensions function public

[phil-opp]

The resize_dimensions would be quite useful when working with imageops::resize and imageops::thumbnail. Unfortunately it's not part of the public API, so downstream crates cannot use it.

This was already requested in #1354 a few years ago. The issue was closed without a comment.

Draft

It would be nice if we could make the function public.

[fintelia]

Looks like there was also an abandoned PR: #1356. For reference (since I didn't remember off hand what it did), this is the implementation of resize_dimensions...

image/src/math/utils.rs

Lines 5 to 40 in 2125965

	/// Calculates the width and height an image should be resized to.
	/// This preserves aspect ratio, and based on the `fill` parameter
	/// will either fill the dimensions to fit inside the smaller constraint
	/// (will overflow the specified bounds on one axis to preserve
	/// aspect ratio), or will shrink so that both dimensions are
	/// completely contained within the given `width` and `height`,
	/// with empty space on one axis.
	pub(crate) fn resize_dimensions(
	width: u32,
	height: u32,
	nwidth: u32,
	nheight: u32,
	fill: bool,
	) -> (u32, u32) {
	let wratio = f64::from(nwidth) / f64::from(width);
	let hratio = f64::from(nheight) / f64::from(height);
	let ratio = if fill {
	f64::max(wratio, hratio)
	} else {
	f64::min(wratio, hratio)
	};
	let nw = max((f64::from(width) * ratio).round() as u64, 1);
	let nh = max((f64::from(height) * ratio).round() as u64, 1);
	if nw > u64::from(u32::MAX) {
	let ratio = f64::from(u32::MAX) / f64::from(width);
	(u32::MAX, max((f64::from(height) * ratio).round() as u32, 1))
	} else if nh > u64::from(u32::MAX) {
	let ratio = f64::from(u32::MAX) / f64::from(height);
	(max((f64::from(width) * ratio).round() as u32, 1), u32::MAX)
	} else {
	(nw as u32, nh as u32)
	}
	}