/** @internal */
export type Phase = "hidden" | "entering" | "shown" | "leaving";
/** @internal */
export type IntersectionState = {
    phase: Phase;
    direction: 1 | -1;
    enterProgress: number;
    leaveProgress: number;
    /** Logical in/out after hysteresis. */
    isIn: boolean;
    /** Last frame's ratio was at or above `threshold`. */
    wasAbove: boolean;
    /** Last frame's ratio was below `leaveThreshold`. */
    wasBelow: boolean;
    /** Virtual time of the last step. */
    lastTime: number;
};
/** @internal */
export declare function createIntersectionState(now: number): IntersectionState;
/**
 * In/out with hysteresis. Updates `wasAbove` / `wasBelow`, not `isIn`.
 * A threshold of 0 counts a touching element as in.
 * @internal
 */
export declare function nextIsIn(state: IntersectionState, ratio: number, touching: boolean, threshold: number, leaveThreshold: number): boolean;
/**
 * Skip a frame without moving progress, e.g. while frozen.
 * The next step then starts from `now`.
 * @internal
 */
export declare function pauseIntersection(state: IntersectionState, now: number): void;
/**
 * Advance the state. Mutates and returns it.
 * `duration` must be above 0.
 * @internal
 */
export declare function stepIntersection(state: IntersectionState, isIn: boolean, now: number, duration: number): IntersectionState;