/**
 * FACSSystem.ts
 *
 * Facial Action Coding System — 52 Action Unit definitions,
 * compound expression presets, 15 viseme mappings, and morph
 * target delta computation utilities.
 *
 * Compatible with Apple ARKit, Unreal MetaHuman, VRM, and VTuber tracking.
 *
 * @see W.240: FACS 52 AUs are the universal facial expression standard
 * @see P.CHAR.001: Shape-Sculpt-to-Morph-Target pipeline
 * @see G.CHAR.001: Sparse morph targets to reduce memory (31MB → 3MB)
 * @module character
 */
export interface ActionUnitDefinition {
    /** FACS AU number (e.g., 1, 2, 4, ...) */
    id: number;
    /** Standard FACS name */
    name: string;
    /** Primary facial region affected */
    region: 'brow' | 'eye' | 'nose' | 'mouth' | 'jaw' | 'tongue' | 'cheek' | 'head' | 'gaze';
    /** Description of the muscular action */
    description: string;
    /** Whether this AU is typically bilateral (left+right) */
    bilateral: boolean;
    /** Apple ARKit blend shape name(s) mapping */
    arkitMapping?: string[];
}
export declare const FACS_ACTION_UNITS: ActionUnitDefinition[];
export interface CompoundExpression {
    name: string;
    weights: Record<number, number>;
}
export declare const EXPRESSION_PRESETS: CompoundExpression[];
export interface VisemeDefinition {
    name: string;
    phonemes: string[];
    weights: Record<number, number>;
}
export declare const VISEME_15: VisemeDefinition[];
export interface VertexDelta {
    /** Index into the vertex buffer */
    vertexIndex: number;
    /** Position delta (dx, dy, dz) */
    delta: [number, number, number];
    /** Normal delta (optional, for smooth lighting) */
    normalDelta?: [number, number, number];
}
export interface SparseMorphTarget {
    /** AU or viseme name */
    name: string;
    /** Only vertices that actually moved (sparse — G.CHAR.001) */
    deltas: VertexDelta[];
    /** Total vertex count of the base mesh */
    totalVertices: number;
}
/**
 * Compute sparse morph target from neutral and deformed meshes.
 *
 * Only stores vertices where the delta exceeds epsilon.
 * This reduces memory from ~31MB (52 AUs x 50K x 12B) to ~3MB.
 *
 * @param neutral - Neutral pose vertex positions (flat Float32Array, 3 values per vertex)
 * @param deformed - Deformed pose vertex positions (same layout)
 * @param epsilon - Minimum delta magnitude to include (default 0.0001)
 * @returns SparseMorphTarget with only affected vertices
 */
export declare function computeSparseMorphTarget(name: string, neutral: Float32Array, deformed: Float32Array, epsilon?: number): SparseMorphTarget;
/**
 * Apply weighted morph targets to a base mesh.
 *
 * @param basePositions - Neutral pose positions (will be modified in place)
 * @param targets - Active morph targets with their weights
 */
export declare function applyMorphTargets(basePositions: Float32Array, targets: Array<{
    target: SparseMorphTarget;
    weight: number;
}>): void;
/**
 * Evaluate a compound expression into individual AU weights.
 */
export declare function evaluateExpression(expressionName: string): Record<number, number>;
/**
 * Get AU definition by ID.
 */
export declare function getActionUnit(id: number): ActionUnitDefinition | undefined;
/**
 * Get viseme definition by name.
 */
export declare function getViseme(name: string): VisemeDefinition | undefined;
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