NITRATE: The Mill

A moonlit silhouette loop rendered in real time in Unity 6 URP. The turning sails of the windmill cut the moonlight on every frame: the light shafts are raymarched through the shadow map, not painted on. All the geometry is generated by code. One black Shader Graph material carries the wind through every pass. A custom Render Graph pipeline adds fog, a depth-blur ladder and a film print.

2.46 ms per frame at 1080p on a laptop GTX 1650 Ti. 11.0 ms at 720p on the laptop's Intel UHD with the Low preset. Both measured in a player build (see Frame budget).

Download the Windows build, run it, and press F9 to measure it on your own GPU. The build is not code-signed, so Windows may show a warning; the SHA-256 of the zip is in the release notes, and you can always build it yourself from this repository.

How it works

1. Geometry. Generators in Assets/Nitrate/Scripts/Generators build every mesh in the editor: ridges with a grass fringe, far ridges with bare trees, trees with hanging moss, reeds, the mill and its sails, the lantern, the rope. The lamplighter is a cut-paper puppet: hand-placed outlines, smoothed and extruded. Nitrate > 2. Build Mill Scene rebuilds everything.
2. Silhouettes. Shaders/Graphs/NitrateSilhouette.shadergraph is unlit black and casts shadows. The wind moves vertices in every pass, shadow caster and depth included, so the shafts blocked by a swaying branch sway with it and depth priming still matches. The generators write the wind response into vertex colour: R is stiffness, G is phase.
3. Atmosphere. Scripts/NitrateAtmosphereFeature.cs and Shaders/NitrateAtmosphere.shader, as Render Graph passes before post-processing:
   • Beams: a raymarch through the main light's shadow map at 1/4 resolution. It takes 16 steps with blue-noise jitter that changes at 24 Hz, then runs a depth-aware separable blur and a bilateral upsample.
   • Composite:
     • fog measured from the figure's plane, so the figure and everything in front of it stay pure black;
     • an analytic sky and moon;
     • a water mirror whose ripples follow the same gusts as the grass;
     • the lantern's glow in fog, in closed form.
   • Depth-blur ladder instead of Bokeh DoF: depth-rejecting blurs at 1/4 and 1/8 resolution, picked per pixel by distance to the figure's plane. The blur works on compressed HDR, c / (1 + luma); without it the moon floods the thin sails.
4. Film print. Shaders/Graphs/NitrateFilm.shadergraph and Scripts/NitrateFilmFeature.cs:
   • a mono tone curve, with saturated warm pixels keeping their colour (the lantern);
   • a vignette, 24 Hz streaky blue-noise grain, flicker, gate weave, dust and scratches;
   • a TPDF dither. The dither needs a 64-bit HDR target, because R11G11B10 quantises it away.
5. Camera and loop. A dolly zoom with a physical-camera lens shift keeps the hub on the upper-right thirds point while the field of view goes from 15° to 38° (Scripts/NitrateDollyZoom.cs). Everything moves on one 15 s clock, with periods that divide the loop, so the loop has no seam.

Shaders/NitrateSilhouette.shader and Shaders/NitrateFilm.shader are the same code as the two graphs, written by hand and kept as a readable reference. Rendered side by side, each graph and its shader differ in fewer than 0.01% of the pixels, from floating-point ordering.

Frame budget

GPU time per frame, median:

	720p High	720p Low	1080p High	1080p Low
GTX 1650 Ti (laptop)	1.22 ms	0.73 ms	2.46 ms	1.31 ms
Intel UHD, i5-10300H (laptop)	16.9 ms	11.0 ms	34.2 ms	19.7 ms (11.2 ms at render scale 0.5)

Method.

• Measured in a Windows player build on D3D11, with FrameTimingManager GPU times.
• 15 configurations: the full look, plus each layer switched off in turn. A layer's cost is the full frame minus the frame without it, so the deltas are not strictly additive.
• Each configuration plays the whole 15 s loop after a warm-up. The run repeats 3 times in alternating order, and the tables use the median.
• The raw CSVs are in benchmarks/.

What the numbers say.

• On the GTX the whole look is a small fraction of a 60 fps budget.
• On the Intel UHD the full-screen passes dominate, especially the atmosphere composite at 1080p. The beams, which the scene is built around, cost 0.14 ms on the GTX and 1.8 ms on the UHD.

Run it

• Unity 6000.6.4f1 (Unity 6.6) with URP 17.6. Tested on Windows with D3D11.
• Open the project and the scene Assets/Nitrate/Scenes/Mill.unity, then press Play. The scene also animates in edit mode (Nitrate > Animate In Edit Mode).
• Nitrate > 1. Configure Project re-applies the URP and project settings. Nitrate > 2. Build Mill Scene regenerates the scene.

Keys in Play mode:

• 1 film, 2 bloom, 3 depth blur, 4 beam mode, 5 atmosphere, 6 lit grey view;
• V debug views, L High/Low preset, M lantern colour, H HUD;
• mouse wheel: dolly, Space: autoplay;
• right mouse drag: move the moon, C: cursor.

Benchmark.

1. Build the player, or download it.
2. Press F9 in the running player. It plays 15 configurations over the loop (about 13 minutes) and writes a CSV next to the exe; the path is shown on screen when it ends.
3. Or start it from a terminal: Nitrate.exe -benchmark -screen-fullscreen 1 -screen-width 1920 -screen-height 1080. Started this way, the player quits when it is done. Optional flags:
   • -passes N and -measure S set the number of passes and the seconds per configuration;
   • -shots <folder> saves one frame per configuration;
   • Unity's -force-device-index N picks the GPU on a laptop with two.

For showing the scene, run it fullscreen: windowed mode on a two-GPU laptop adds occasional presentation stalls.

Project layout

Assets/Nitrate/
  Scripts/             atmosphere and film features, clock, camera, controls, benchmark
  Scripts/Generators/  mesh builder and the procedural generators
  Shaders/             atmosphere passes, common HLSL, hand-written reference shaders
  Shaders/Graphs/      Silhouette and Film Shader Graphs, custom-function HLSL
  Editor/              project setup, scene builder, verification, blue-noise generator
  Materials/  Scenes/  Textures/  Settings/
benchmarks/            measured CSVs
media/                 images used in this README

Known limitations

• The depth-blur radius is set in texels of the 1/4-resolution target, so at 4K the background looks crisper than at 1080p.
• The GPU Resident Drawer is disabled: it uploads transforms only at frame boundaries, and the offline frame renderer poses the scene in the middle of a frame.
• The blue-noise texture is generated in the editor (void-and-cluster, Ulichney 1993). URP's built-in blue noise is Alpha8, which reads 0 in the red channel.

License

MIT