From-scratch C# - BCL only

One ray tracer. Every law of physics it can prove.

Reality Sim is a single hand-written engine: a recursive Whitted-style ray tracer bolted to an SI-unit physics solver. It does not paint reflections, hit-points, or animation loops - it solves for them. Mirrors reflect because a ray genuinely bounces; a door opens because a latch joint failed under real torque; iron glows because the blackbody curve says so. Roughly 40 proof GIFs come out of the one engine, and every pixel is written with the .NET base library plus a GIF encoder and a seeded RNG. No shaders, no scene files, no assets.

~40

proof GIFs from one engine

self-test modules, 36 assertions

libraries beyond GIF + RNG

net10.0

warnings-as-errors, 0/0 build

Six renders

Different scenes, one solver behind all of them

A dim brick power hall lit by a glowing furnace and a lamp, with a generator drum and a waterwheel casting soft ray-traced shadows

GRAND POWER HALL

The whole energy chain, one SI sim

Falling water turns a wheel, a shaft, a copper-coil generator, then a lamp; a fire drives a boiler through sensible and latent heat to steam pressure, a piston, a crank, and a train. Ray-traced with soft shadows and a warm furnace glow. 84 frames, rendered at 13.5 fps.

A tall dim atrium with a single glowing cylinder and drifting media, translucent boxes and volumetric haze along the floor

DROP ATRIUM

Five falls through air, flame and water

Objects are released together under real gravity, drag, buoyancy, the Magnus effect and lift, then fall through different media. The sim decides every position; the ray tracer only lights what the physics put there - volumetric haze, translucency and all.

Molten iron droplets glowing yellow-white in a forge crucible beside a temperature and blackbody-radiation readout panel

FORGE / INCANDESCENCE

Iron to 1538 C, coloured by physics

Glow colour comes from the Wien blackbody curve, brightness from Stefan-Boltzmann (radiated power scales as roughly T to the fourth), and the temperature parks on a latent-heat plateau at the melt. The debug panel prints the energy accounting live, in J/g.

A lit candle with a teardrop flame casting warm light, beside a four-zone thermal readout for solid wax, melt pool, wick vapour and flame

CANDLE STATION

Four thermal zones, and lost mass

Solid wax, a melt pool, wick vapour, then a combustion flame - the one station where the phase change is chemical and the system loses mass, burning wax to CO2 and H2O. Around 42 kJ per gram released, tracked against the melt cost.

A six-camera door render grid stacked over eight labelled debug panels: depth, material id, joint stress, force arrows, velocity, night-vision, red-relight and stats

DOOR AS AN ASSEMBLY

A door is joints, not an HP bar

Six beauty cameras over an eight-panel debug strip - depth, material id, joint stress, Newton-scaled force arrows, velocity, a night-vision sensor, a red-only relight, and stats. Each pose (shut, sagging, hanging from the latch, swung open, detached) is decided by which joints survived.

A large red mirrored sphere flanked by smaller dark spheres, reflecting each other on a soft grey floor

RECURSIVE MIRROR PROOF

Reflections solved, not painted

TraceRay genuinely recurses on the reflected direction, Fresnel-Schlick blended and energy-bounded by bounce depth. A self-test aims a ray at a sphere's exact mirror-image point and checks it lands back on the sphere after one real bounce. Facing mirrors stay bounded, no blow-up.

Every tile links to its full GIF. Renders are pixel-exact engine output, captured statically - nothing here is a video codec or a post-filter.

How it renders

THE RAY TRACER

A recursive Whitted-style tracer: ray-sphere, ray-plane and ray-box intersection with outward normals, specular reflection off Vec3.Reflect, Fresnel-Schlick blending, then sRGB and an ACES filmic tonemap on the way out. A from-scratch 3x5 bitmap font labels every debug panel directly in the pixels.

THE PHYSICS

SI units throughout: impulse and lever-arm torque distributed into a joint graph with real shear and torque limits; gravity, drag, buoyancy and Magnus lift for falling bodies; sensible plus latent heat, Wien and Stefan-Boltzmann radiation, and Faraday's law for the phase and energy stations. Energy is ledgered - no free energy, and the tests assert it.

What the self-tests actually assert

Seven modules, 36 assertions, all passing - real invariants, not "looks right". A ray aimed at a sphere's mirror-image point lands back on the sphere after one bounce. Reaction forces at a kick sum exactly to the impact force, inventing no energy. A kick near the latch delivers more latch force than the identical kick near the hinge - and pushing a door against its built-in stop leaks under 10% of the force it would toward opening. sRGB round-trips; the ACES tonemap stays monotonic; facing mirrors recurse without NaN or blow-up. The material figures (pine, mild steel, soda-lime glass) are cited, order-of-magnitude values, stated as such.