import { Atlas } from '../types/Atlas';
import { Integer } from '../types/Integer';
import { Milliseconds } from '../types/Milliseconds';
/** Record and update an Atlas.Animation's state. */
export interface Animator {
    /** Cel index oscillation state. This integer may fall outside of animation
        bounds depending on the animation interval selected by direction. This
        value should be carried over from each call unless the cel is manually
        set. Any integer in [0, length - 1] is always valid. */
    period: Integer;
    /** Current cel exposure in milliseconds. When the fractional value meets or
        exceeds the cel exposure duration, the cel is advanced according to
        direction. This value should be carried over from each call with the
        current time step added, and zeroed on manual cel change. */
    exposure: Milliseconds;
}
export declare namespace Animator {
    /** Apply the time since last frame was shown, possibly advancing the
        animation period. */
    function animate(period: Integer, exposure: Milliseconds, animation: Atlas.Animation): Animator;
    /** @return The animation cel index. */
    function index(period: Integer, cels: readonly Atlas.Cel[]): number;
}