/**
 * Lighting environment for the main shading pipelines and the procedural
 * sky pass.
 *
 * Every field is optional; the defaults reproduce the renderer's historical
 * hardcoded look exactly (sun at normalize(0.5, 1, 0.3), hemisphere ambient,
 * 0.85 exposure), so callers that never pass `RenderOptions.environment`
 * see no visual change.
 *
 * Directions are in viewer/world space (Y-up). `sunDirection` points TOWARD
 * the sun, matching the shader's `dot(N, sunDirection)` convention.
 */
export type Vec3Color = [number, number, number];
export interface SkyGradient {
    /** Colour straight up. */
    zenith: Vec3Color;
    /** Colour at the horizon band. */
    horizon: Vec3Color;
    /** Colour below the horizon. */
    ground: Vec3Color;
}
export interface LightingEnvironment {
    /** Unit vector toward the sun (Y-up viewer space). Normalized defensively. */
    sunDirection?: [number, number, number];
    sunColor?: Vec3Color;
    /** Diffuse strength of the sun term (historic default 0.55). */
    sunIntensity?: number;
    /** Hemisphere-ambient sky colour (historic default [0.3, 0.35, 0.4]). */
    skyColor?: Vec3Color;
    /** Hemisphere-ambient ground colour (historic default [0.15, 0.1, 0.08]). */
    groundColor?: Vec3Color;
    /** Hemisphere ambient strength (historic default 0.25). */
    ambientIntensity?: number;
    /** Fixed fill-light strength (historic default 0.15). */
    fillIntensity?: number;
    /** Rim-light strength (historic default 0.15). */
    rimIntensity?: number;
    /** Pre-tonemap exposure multiplier (historic default 0.85). */
    exposure?: number;
    /**
     * Draw the procedural sky background. When false (default) the frame
     * clears to `RenderOptions.clearColor` exactly as before.
     */
    skyEnabled?: boolean;
    /**
     * Optional explicit sky gradient for the sky pass. When omitted, a
     * palette is derived from the sun's altitude (day → golden hour →
     * twilight → night).
     */
    sky?: Partial<SkyGradient>;
}
/** `LightingEnvironment` with every field populated. */
export type ResolvedEnvironment = Required<Omit<LightingEnvironment, 'sky'>> & {
    sky: SkyGradient;
};
/**
 * Derive a sky gradient from the sun's elevation (the Y component of the
 * unit sun direction = sin(altitude)). Four keyed palettes blended smoothly:
 * night → twilight → golden hour → day.
 */
export declare function deriveSkyGradient(sunElevation: number): SkyGradient;
/** Fill in defaults; the result always renders identically to the legacy look when `env` is undefined/empty. */
export declare function resolveEnvironment(env?: LightingEnvironment): ResolvedEnvironment;
/** Byte size of the packed environment UBO (must match the WGSL struct). */
export declare const ENVIRONMENT_UNIFORM_SIZE = 80;
/**
 * Pack the resolved environment into the `Environment` WGSL struct layout:
 *
 *   sunDirection: vec3 + sunIntensity: f32      → floats 0..3
 *   sunColor: vec3     + ambientIntensity: f32  → floats 4..7
 *   skyColor: vec3     + exposure: f32          → floats 8..11
 *   groundColor: vec3  + fillIntensity: f32     → floats 12..15
 *   rimIntensity: f32  + 3 pad floats           → floats 16..19
 */
export declare function packEnvironmentUniforms(env: ResolvedEnvironment, out?: Float32Array): Float32Array;
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