/**
 * A single stop on a parsed CSS gradient. `offset` ∈ [0, 1].
 */
export interface GradientStop {
    offset: number;
    color: [number, number, number, number];
}
/**
 * Parse a `linear-gradient(...)` CSS expression into ordered stops. Tolerates
 * missing percentages (distributes linearly between known offsets, matching
 * the CSS standard) and leading direction tokens (`to right`, `90deg`, etc.)
 * which are simply skipped.
 *
 * Returns the default blue → orange two-stop on any parse failure so themes
 * that never set the gradient still produce sane output.
 */
export declare function parseCssGradient(src: string | null | undefined): GradientStop[];
/**
 * Piecewise-linear color sample at `t ∈ [0, 1]`. Returns RGBA in [0, 1].
 * Clamps `t` to the gradient's first/last stop outside `[0, 1]`.
 */
export declare function sampleGradient(stops: GradientStop[], t: number): [number, number, number, number];
/**
 * Sign-aware normalization. Returns `t ∈ [0, 1]` where the 50% stop is
 * always the sign pivot:
 *   - crosses zero → `[-maxAbs, maxAbs]` stretched symmetrically; 0 → 0.5.
 *   - all-positive → `[0, colorMax]` occupies top half `[0.5, 1]`.
 *   - all-negative → `[colorMin, 0]` occupies bottom half `[0, 0.5]`.
 *   - degenerate   → 0.5 (single colour at the midpoint).
 */
export declare function colorValueToT(value: number, colorMin: number, colorMax: number): number;
/**
 * Convert a discrete series palette (from `--psp-charts--series-N--color`)
 * into a `GradientStop[]` with stops at `i / (N - 1)`. The resulting
 * stops can feed `buildGradientLUT` / `ensureGradientTexture` / any
 * other code path that already accepts a gradient — so categorical
 * coloring and numeric gradients share one LUT pipeline. Integer idx
 * sampling via `t = idx / (N - 1)` lands exactly on a palette color;
 * the linear blend between stops is only hit by non-integer samples
 * (which categorical data doesn't produce).
 */
export declare function paletteToStops(palette: [number, number, number][]): GradientStop[];
/**
 * Bake a sampled LUT for GPU upload as RGBA8 (`size × 1`). Default 256
 * samples — visually indistinguishable from a denser sample at typical
 * viewport sizes and keeps the texture tiny (1 KB).
 */
export declare function buildGradientLUT(stops: GradientStop[], size?: number): Uint8Array;