/**
 * MLSMPMFluid — GPU-accelerated MLS-MPM fluid simulation.
 *
 * Uses WebGPU compute shaders for Moving Least Squares Material Point Method:
 *   Frame pipeline:
 *     [1] Grid Clear
 *     [2] Particle-to-Grid (P2G) — scatter mass/momentum via atomicAdd
 *     [3] Grid Update — gravity, boundaries, momentum → velocity
 *     [4] Grid-to-Particle (G2P) — gather velocity, update APIC C matrix + J
 *
 *   Rendering pipeline (SSFR):
 *     [1] Depth pass — particle → depth buffer
 *     [2] Thickness pass — additive particle thickness
 *     [3] Bilateral filter — smooth depth, compute normals
 *     [4] Final shade — Fresnel + Beer-Lambert + refraction
 *
 * Performance targets:
 *   - 100K particles @ 60 FPS on iGPU
 *   - 300K particles @ 30 FPS on discrete GPU
 *
 * @module physics
 */
export interface MLSMPMConfig {
    /** Fluid behavior: liquid (incompressible) or gas (compressible) */
    type: 'liquid' | 'gas';
    /** Number of simulation particles */
    particleCount: number;
    /** Dynamic viscosity (default: 0.01 for water) */
    viscosity: number;
    /** Grid cells per axis (default: 128) */
    gridResolution: number;
    /** Domain size in world units (default: 10) */
    domainSize: number;
    /** SSFR render resolution scale (0.5 = half-res, default) */
    resolutionScale: number;
    /** Target rest density (default: 1000 for water) */
    restDensity: number;
    /** Compressibility stiffness (default: 50) */
    bulkModulus: number;
    /** Particle visual radius (default: 0.02) */
    particleRadius: number;
    /** Gravity Y component (default: -9.81) */
    gravity: number;
    /** SSFR absorption color RGB (default: [0.4, 0.04, 0.0] blue water) */
    absorptionColor: [number, number, number];
    /** SSFR absorption strength (default: 2.0) */
    absorptionStrength: number;
}
export interface MLSMPMStats {
    particleCount: number;
    gridResolution: number;
    lastStepMs: number;
    lastRenderMs: number;
    gpuBufferSizeMB: number;
}
export declare class MLSMPMFluid {
    private config;
    private device;
    private disposed;
    private particlePositions;
    private particleVelocities;
    private particleC;
    private particleJ;
    private gridMass;
    private gridMomentumX;
    private gridMomentumY;
    private gridMomentumZ;
    private gridVelocity;
    private simParamsBuffer;
    /** External force (wind) applied during grid update [x, y, z] in m/s² */
    private externalForce;
    private gridClearPipeline;
    private p2gPipeline;
    private gridUpdatePipeline;
    private g2pPipeline;
    private p2gBindGroup;
    private gridClearBindGroup;
    private gridUpdateBindGroup;
    private g2pBindGroup;
    private lastStepMs;
    private lastRenderMs;
    constructor(config?: Partial<MLSMPMConfig>);
    /**
     * Initialize GPU resources and compile shaders.
     * Must be called before step().
     */
    init(device: GPUDevice): Promise<void>;
    /**
     * Set initial particle positions. Call after init().
     *
     * @param positions - Float32Array of [x, y, z, volume, ...] per particle
     */
    setInitialPositions(positions: Float32Array): void;
    /**
     * Generate a block of particles in a cubic region.
     */
    generateParticleBlock(min: [number, number, number], max: [number, number, number]): Float32Array;
    /**
     * Step the simulation forward by dt seconds.
     */
    step(dt?: number): void;
    /**
     * Dispose all GPU resources.
     */
    dispose(): void;
    /**
     * Set an external force (e.g. wind) applied to the fluid during grid update.
     * Force is in world-space acceleration (m/s²). Applied additively with gravity.
     */
    setExternalForce(x: number, y: number, z: number): void;
    /** Get the particle position buffer for rendering or unified PBD integration */
    getParticlePositionBuffer(): GPUBuffer | null;
    /** Get the particle velocity buffer */
    getParticleVelocityBuffer(): GPUBuffer | null;
    getParticleCount(): number;
    getConfig(): Readonly<MLSMPMConfig>;
    getStats(): MLSMPMStats;
    private createPipelines;
    private createBindGroups;
    private updateUniforms;
}
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