# Are the `frames` valid for an animation? (see the requirements in `frames`)
	var valid: Bool is lazy do
		var r: nullable RootTexture = null
		for f in frames do
			if r == null then
				r = f.root
			else
				if r != f.root then return false
			end
		end

		# TODO check for line, constant distance, and same aspect ratio.

		return true
	end