You could fix this by deriving the function from some initial state, and then when resizes occur you just take a snapshot of the current animation state, freeze

You could fix this by deriving the function from some initial state, and then when resizes occur you just take a snapshot of the current animation state, freeze the animation until resizing stops, and replace the function with a new one derived from your previous initial state. So this does require _some_ state but only to initialize.