AetherCoreEngine

Zero-Dependency Multithreaded 3D Spectral Path Tracer, 3D Incompressible Navier–Stokes Fluid Solver & Procedural 24-Bit Spatial Audio Engine in Pure Rust (std only)

Audio Output: renders/simulation_soundtrack.wav (48,000 Hz, 24-bit signed stereo PCM, 15.00 s spatial soundtrack driven directly by the 3D fluid simulation's kinetic energy, vorticity, and plume center-of-mass).

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Architectural Highlights

Built from scratch in Rust with zero external crates ([dependencies] is completely empty in Cargo.toml):

1. BVH-Accelerated Monte Carlo Hero-Wavelength Spectral Path Tracer

• 3D Linear Algebra & Spectral Radiometry (src/math.rs, src/rng.rs):
  • Complete Vec3, Vec4, Mat3, Mat4 (exact cofactor/adjugate inversion), Hamilton Quat (Rodrigues rotation, slerp, matrix conversion), Duff branchless orthonormal basis (Onb), and IEEE-754 Kay–Kajiya slab Aabb.
  • 4-Wavelength Hero Wavelength Spectral Sampling (Wavelengths4, Spectrum4, $380\text{–}750\text{ nm}$), Wyman–Sloan–Shirley CIE 1931 $2^\circ$ standard observer matching functions calibrated to the D65 whitepoint, partition-of-unity smooth spectral reflectance/emission curves (SpectralCurve), and Stephen Hill's ACES Filmic RRT+ODT tone mapping.
• SAH BVH & Hybrid Geometry (src/primitives.rs, src/bvh.rs):
  • Supports Triangles (Möller–Trumbore + uniform barycentric surface sampling), Analytic Spheres, and composable CSG Signed-Distance Primitives (RoundBox, Torus, Cylinder, Sphere, Octahedron, rigid Transform, Union, SmoothUnion, Intersection, Difference) intersected via Lipschitz-pruned Sphere Tracing with 6-step bisection root polishing and 4-tap tetrahedral central-difference normals.
  • 16-bin Surface Area Heuristic (SAH) BVH builder flattened into contiguous depth-first linear nodes (LinearBvhNode) with allocation-free front-to-back stack traversal.
• Physically Based Spectral BSDFs & Next Event Estimation (src/bsdf.rs, src/renderer.rs):
  • Dielectric: Exact unpolarized Fresnel equations + Snell refraction + Total Internal Reflection + Cauchy chromatic dispersion ($n(\lambda) = n_0 + B/\lambda^2$) + Beer–Lambert volumetric absorption ($\exp(-\sigma_a(\lambda) d)$).
  • Conductor: Exact Born & Wolf complex conductor Fresnel ($\eta(\lambda) + i k(\lambda)$), Trowbridge–Reitz anisotropic GGX microfacet distribution, height-correlated Smith $G_2$ shadowing-masking, and Heitz (2018) VNDF importance sampling.
  • Subsurface Isotropic Volumetric Scattering: Unbiased Monte Carlo multi-scattering random walk inside translucent solid media (sigma_s, sigma_a, exponential free-flight sampling, isotropic phase function).
  • Multiple Importance Sampling (MIS): Power heuristic ($\beta = 2$) combining power-weighted area-light Next Event Estimation (LightEntry CDF) with BSDF and volumetric phase sampling.
• Multithreaded Work-Stealing Tile Renderer & Custom PNG Codec (src/renderer.rs, src/png.rs):
  • Center-out spiral 16x16 tile ordering across per-worker VecDeque<TileJob> queues with cross-worker LIFO/FIFO work-stealing and per-tile nanosecond latency/throughput instrumentation.
  • From-scratch IEEE 802.3 CRC-32, RFC 1950 Adler-32 / zlib, and RFC 1951 LZ77 sliding-window + Fixed Huffman DEFLATE PNG encoder & verifier (plus .ppm and .bmp codecs).

2. 3D Incompressible Navier–Stokes Eulerian Fluid & Vorticity Confinement Solver (src/fluid.rs)

• Second-order MacCormack advection with local 8-cell trilinear extrema clamping (preventing numerical oscillation and guaranteeing non-negative smoke density $\rho \ge 0$).
• Staggered Marker-and-Cell (MAC) Helmholtz–Hodge Poisson pressure projection ($\nabla^2 p = \frac{1}{\Delta t}\nabla\cdot\mathbf{u}^*$) with both Matrix-Free Conjugate Gradient (CG) and Red-Black SOR Gauss–Seidel solvers.
• 3D Vorticity Confinement ($\mathbf{f}_{\text{conf}} = \epsilon h (\mathbf{N} \times \boldsymbol{\omega})$) and Boussinesq thermal buoyancy.
• Coupled directly into the spectral path tracer as a heterogeneous participating medium (FluidMedium) via Woodcock Delta Tracking, Novak Ratio Tracking volumetric shadow transmittance, and Henyey–Greenstein phase sampling.

3. Offline Procedural Synthesizer & 24-Bit WAV Soundtrack Generator (src/audio.rs)

• Synthesizes a 15.0-second, 48,000 Hz, 24-bit stereo soundtrack (720,000 frames, TPDF-dithered RIFF/WAVE) driven by the fluid solver's time-series telemetry:
  • 16-voice polyphonic 4-Operator DX-style FM Crystalline Bells with kinetic-energy-modulated harmonic indices.
  • Bandlimited PolyBLEP detuned synth pad & sub-bass sculpted by a cascaded 24 dB/oct 4-Pole Zero-Delay Feedback TPT State-Variable Filter (Vadim Zavalishin ZDF topology).
  • 8-Line Orthogonal Sylvester–Hadamard Feedback Delay Network (FDN) cathedral reverb (hadamard8_normalized fast Walsh–Hadamard butterfly + $RT_{60}$ two-band absorption + quadrature LFO delay modulation) and binaural Interaural Time Difference (ITD) spatialization.

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Verification & Benchmark Results (1280x720 @ 48 SPP, 8 Threads)

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 AUTOMATED SELF-TEST & INVARIANT VERIFICATION SUITE (6/6 PASSED)
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 [PASS] Math / Quat / Mat4^-1 / ONB / Checksums              | max |M*M^-1 - I| = 4.44e-16, ONB ortho = 1.40e-17
 [PASS] SAH BVH Invariants & Ray Equivalence                 | 87 nodes (44 leaves, depth 10), 1785/2500 hits exact (max |dt|=0.00e0)
 [PASS] BSDF & Subsurface Energy Conservation                | Fresnel R+T=1.000000, GGX Furnace peak=0.9926<=1.0, SSS absorb<conserv
 [PASS] 3D Navier-Stokes CG Poisson Projection               | ||div u||_2: 2.5751e0 -> 6.7289e-3 (99.7% reduction)
 [PASS] PNG Binary Header / CRC32 / Adler32 / LZ77 Roundtrip | 1280x720 8-bit RGB, 7 chunks, 2407.2 KB lossless DEFLATE verified
 [PASS] WAV 24-Bit 48kHz Stereo RIFF Header & Spatial Signal | 720000 frames (15.00s), RMS L=0.158 R=0.184, Peak=0.688, StereoDiff=0.166

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 WORK-STEALING RENDERER THROUGHPUT & LATENCY PERCENTILE BENCHMARKS
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 Total Rays Traced        : 203050212 (44.237M camera samples across 3600 tiles)
 Work-Stealing Scheduler  : 731 cross-worker tile steals across 8 threads
 Aggregate Wall Throughput: 2.089 MRays/sec  |  0.455 MSamples/sec  (Wall: 97.204s)
 Per-Tile Throughput (MRays/sec) :  p50 =   0.358  |  p95 =   0.679  |  p99 =   0.786
 Per-Tile Latency    (millisec)  :  p50 = 157.467  |  p95 = 573.245  |  p99 = 1090.189

Quick Start

# Run full unit & integration test suite (16 tests)
cargo test --release

# Run full production pipeline (fluid solver -> path tracer -> audio synthesizer -> verification)
cargo run --release

# Custom resolution / sample count override
cargo run --release -- --width 1280 --height 720 --spp 48 --fluid-steps 120