Linearly Transformed Cosines in Feather

A C#/.NET 10 reproduction of Real-Time Polygonal-Light Shading with Linearly Transformed Cosines, built on top of Feather.

Requirements

• .NET SDK 10.0.301, or a compatible .NET 10 SDK.
• A Feather-supported GPU/runtime.
• NuGet restore. FeatherCompute is referenced from Directory.Packages.props.

The SDK version is pinned in global.json, so Rider and the CLI should pick the same SDK:

dotnet restore LTC.sln
dotnet build LTC.sln

Run The Viewers

Standalone LTC viewer:

dotnet run --project src/Ltc.Viewer

Sponza viewer:

dotnet run --project src/Ltc.Sponza

By default, both viewers look for:

data/generated/ltc_fit_64x64.js
assets/lights/images.png

Ltc.Sponza also auto-loads:

assets/sponza

You can pass explicit paths when needed:

dotnet run --project src/Ltc.Viewer -- \
  --lut data/generated/ltc_fit_64x64.js \
  --light-texture assets/lights/images.png

dotnet run --project src/Ltc.Sponza -- \
  --sponza assets/sponza \
  --light-texture assets/lights/images.png

Controls

src/Ltc.Viewer:

• Left-drag: rotate the camera.
• Arrow keys: rotate the light.
• Q / E: roughness down / up.
• A / D: light width down / up.
• W / S: light height up / down.
• Z / X: intensity down / up.
• R / F: texture LOD bias up / down.
• [ / ]: fewer / more ray-tracing comparison samples.
• Space: toggle two-sided lighting.
• T: toggle textured light.
• C: switch LTC / ray-traced ground truth / split / error view.
• G: toggle debug grid.
• Esc: exit.

src/Ltc.Sponza:

• Left-drag: rotate the camera.
• W / A / S / D: move the camera.
• Q / E: roughness down / up.
• Z / X: intensity down / up.
• Hold Shift: move or adjust faster.
• Esc: exit.

Captures

The viewers can write .tga captures:

dotnet run --project src/Ltc.Viewer -- \
  --capture data/generated/viewer.tga \
  --width 1280 \
  --height 720 \
  --msaa 4

dotnet run --project src/Ltc.Sponza -- \
  --capture data/generated/sponza.tga \
  --width 1280 \
  --height 720 \
  --msaa 4

The standalone viewer also has a ray-traced comparison mode:

dotnet run --project src/Ltc.Viewer -- \
  --compare-mode split \
  --rt-grid 16

Fit The LUT

Quick GPU/runtime check:

dotnet run --project src/Ltc.Fit -- --probe-gpu

Fit one preview cell:

dotnet run --project src/Ltc.Fit -- --fit-cell --preview

Fit a tiny preview table:

dotnet run --project src/Ltc.Fit -- \
  --fit-table \
  --preview \
  --output data/generated/ltc_fit_4x4.js

Fit the full 64x64 table:

dotnet run --project src/Ltc.Fit -- \
  --fit-table \
  --size 64 \
  --output data/generated/ltc_fit_64x64.js \
  --checkpoint-csv data/generated/ltc_fit_64x64.csv

Resume from a checkpoint:

dotnet run --project src/Ltc.Fit -- \
  --fit-table \
  --size 64 \
  --resume-csv data/generated/ltc_fit_64x64.csv \
  --output data/generated/ltc_fit_64x64.js

The full table is slow enough that checkpointing is useful. It fits 4096 table cells, and each cell runs a small optimization problem with a multiple-importance-sampling L3 loss.

To evaluate a packed LUT:

dotnet run --project src/Ltc.Fit -- \
  --eval-js-loss \
  --lut data/generated/ltc_fit_64x64.js

Project Layout

assets/lights/      Default image used by textured polygonal lights.
assets/sponza/      Crytek Sponza OBJ scene and textures.
data/generated/     LUTs, checkpoints, captures, and local caches.
src/Ltc.Core/       Table configuration and shared core types.
src/Ltc.Feather/    Feather kernels, fitting code, LUT packing, LUT evaluation.
src/Ltc.Fit/        CLI for fitting and checking LUTs.
src/Ltc.Viewer/     Small LTC viewer.
src/Ltc.Sponza/     Sponza renderer.
tests/              Unit tests for core, fitting, packing, and viewer helpers.

Generated Files

Only these generated files are meant to be tracked:

data/generated/.gitkeep
data/generated/ltc_fit_64x64.js

These stay local:

data/generated/*.csv
data/generated/*.log
data/generated/*.tga
data/generated/light-texture-cache/

So the default viewer works after cloning, but training checkpoints, logs, captures, and cache files do not pollute the repository.

Third-Party Assets

The Sponza scene is the fixed Crytek Sponza OBJ model. See assets/sponza/README.md and THIRD_PARTY_NOTICES.md.

The default light texture lives at assets/lights/images.png.

License

This project is licensed under the MIT License. See LICENSE.

Third-party assets keep their original attribution and license terms. See THIRD_PARTY_NOTICES.md.