# Animation for sprites, set with `Sprite.animate`
#
# Two main services create animations:
# * The constructors accepts an array of textures and the number of frames per
#   seconds: `new Animation(array_of_subtextures, 10.0)`
# * The method `Texture::to_animation` uses the whole texture
#   dividing it in frames either on X or Y:
#   `new Texture("path/in/assets.png").to_animation(30.0, 0, 12)`
class Animation

	# Frames composing this animation
	#
	# All frames must share the same `Texture::root`, be on a vertical or
	# horizontal line, be spaced equally and share the same dimensions.
	var frames: SequenceRead[Texture]

	# Frames per seconds, a higher value makes this animation faster
	#
	# The animation speed is also affected by `SpriteSet::time_mod`.
	var fps: Float

	# 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
end