import type { TreeChartBase } from "./tree-chart";
import type { Vec3 } from "../../theme/palette";
import { type GradientStop } from "../../theme/gradient";
/**
 * Perceptual luminance for a 0..1 RGB triple. Used by tree-chart label
 * painters to pick a contrasting text color over each leaf's fill.
 */
export declare function luminance(r: number, g: number, b: number): number;
/**
 * Sample a gradient and drop the alpha channel. Treemap / sunburst
 * fills carry alpha separately (see {@link leafRGBA}); this is the
 * "just give me the RGB" entry point.
 */
export declare function sampleRGB(stops: GradientStop[], t: number): [number, number, number];
/**
 * Resolve a leaf's fill color according to the chart's color mode:
 *   - `"numeric"` — sign-aware gradient sample via `colorValueToT`.
 *   - `"series"` / `"empty"` — discrete palette lookup keyed by the
 *     node's `colorLabel` (composite of group_by levels in series mode;
 *     `""` in empty mode, which maps to `palette[0]`).
 *
 * Returns RGB only; the alpha channel is applied separately by
 * {@link leafRGBA} using `negativeAlpha` for leaves whose raw size was
 * negative.
 */
export declare function leafColor(chart: TreeChartBase, nodeId: number, stops: GradientStop[], palette: Vec3[]): [number, number, number];
/**
 * `leafColor` + an alpha channel. Negative-size leaves receive
 * `negativeAlpha` (mirrors `theme.areaOpacity` for area charts) so
 * they stay visually distinguishable from positive leaves without
 * disappearing.
 */
export declare function leafRGBA(chart: TreeChartBase, nodeId: number, stops: GradientStop[], palette: Vec3[], negativeAlpha: number): [number, number, number, number];