/**
 * Gravity-correct refill geometry for tumble cascades.
 *
 * Two distinct moments use the same algorithm with different inputs:
 *
 *   - **Moment A (initial drop):** `winnerRows = []`. The entire visible
 *     column is treated as "new". every row falls in from above the
 *     viewport. The vertical distance per row is `visibleRows` cells, so
 *     all rows arrive at their grid positions in the same beat.
 *
 *   - **Moment B (cascade refill):** `winnerRows` lists the rows whose
 *     symbols were removed by the most recent win. Survivors slide DOWN
 *     to fill the gaps below them; new symbols enter from above into the
 *     top holes. The new grid follows the server convention that survivors
 *     keep their relative order and pack to the bottom, with `winnerRows.length`
 *     new symbols stacked above them.
 */
/** A cell coordinate on the reel set. `reel` is column, `row` is visible row. */
export interface Cell {
    reel: number;
    row: number;
}
export interface DropOffset {
    /** Visible row in the new grid (top-to-bottom, 0-indexed). */
    row: number;
    /**
     * Where this symbol "came from" expressed as a virtual row index. Negative
     * values indicate "above the viewport" (e.g. -1 is one cell above row 0).
     * Non-negative values indicate "this row in the OLD grid". a survivor.
     */
    originalRow: number;
    /**
     * Number of cells this symbol must traverse downward. Equals
     * `row - originalRow`. Zero means the symbol stays put (no animation).
     */
    offsetRows: number;
}
/**
 * Compute per-row drop offsets for one reel given its winner set.
 *
 * Returns one entry per visible row, top-to-bottom. Rows with
 * `offsetRows === 0` should NOT be animated. they're survivors that
 * didn't move.
 *
 * **Convention** (Moment B): the new grid must place new symbols at the
 * top `winnerRows.length` rows and survivors at the bottom rows in their
 * original top-to-bottom order. This matches how server-side gravity
 * simulations emit cascade results.
 *
 * @param options.initial - When `true` (Moment A. the player's first
 *   spin click), every row is treated as new regardless of `winnerRows`
 *   (which is normally empty for initial spins). When `false` (Moment B
 *  . cascade refill), an empty `winnerRows` means *no movement on this
 *   reel*; survivor reels in a refill correctly return all-zero offsets.
 *   Default `false` so callers can't accidentally trigger a full re-drop
 *   on a reel that had no winners.
 */
export declare function computeDropOffsets(visibleRows: number, winnerRows: readonly number[], options?: {
    initial?: boolean;
}): DropOffset[];
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