NPR hatching renderer based on globally optimal direction fields and stripe patterns on triangle meshes. Implements the full pipeline from two papers by Knoeppel, Crane, Pinkall, and Schroeder (SIGGRAPH 2013 & 2015), producing pen-and-ink style illustrations where stripe width encodes shading.
- Globally optimal direction fields (Knoeppel et al. 2013) — smooth curvature-aligned 2-direction fields via sparse eigenvalue problem with Cholesky factorization
- Stripe patterns (Knoeppel et al. 2015) — globally continuous texture coordinates on the implicit double cover, singularity handling via lArg interpolant
- NPR hatching shader — stripe width modulated by diffuse shading, silhouette and contour edges, antialiased rendering
- Interactive controls — dark/bright threshold, shading amount, stripe frequency, line frequency, perpendicular field toggle
- Web version — Emscripten/WebAssembly build with WebGL2, drag-and-drop OBJ/OFF loading, no server required
Requires CMake 3.20+ and a C++20 compiler. All dependencies (Eigen, GLFW, glad, Dear ImGui, tinyobjloader, GoogleTest) are fetched automatically.
cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build buildRequires the Emscripten SDK.
cd web
mkdir build &&cd build
emcmake cmake ..
emmake make -j8Serve web/build/ with any HTTP server (e.g. python3 -m http.server 8080) and open in a browser.
./build/hatching # Loads bunny.obj from current directory
./build/hatching mesh.obj # Load an OBJ file
./build/hatching mesh.off # Load an OFF file| Input | Action |
|---|---|
| Left drag | Rotate camera |
| Right drag | Pan camera |
| Scroll | Zoom |
| Arrow keys | Rotate light direction |
cmake --build build --target hatching_tests
ctest --test-dir build -R "^(Mesh\|Direction\|Stripe\|Geometry)"42 tests covering mesh topology, discrete differential geometry operators, direction field computation, and the full stripe pattern pipeline.
doxygen Doxyfile
open docs/doxygen/html/index.htmlsrc/
triangle_mesh.h/cpp Mesh data structure with edge list and adjacency
geometry.h/cpp Angle rescaling, parallel transport, holonomy,
cotangent weights, Hopf differential
direction_field.h/cpp Energy/mass matrices, eigenvalue solve,
curvature alignment, singularity indices
stripe_pattern.h/cpp Edge data, stripe energy, inverse power iteration,
texture coordinate extraction (Algorithms 3-7)
renderer.h/cpp OpenGL hatching renderer
camera.h/cpp Orbit camera
main.cpp Desktop application entry point
shaders/
hatching.vert/frag NPR hatching shader with lArg interpolant
web/
src/bridge.cpp Emscripten bindings for hatching_core
js/ WebGL2 renderer, orbit camera, application logic
index.html Browser UI with drag-and-drop and sliders
tests/
test_*.cpp 42 unit tests
- F. Knoeppel, K. Crane, U. Pinkall, P. Schroeder. Globally Optimal Direction Fields. ACM Trans. Graph. 32(4), 2013.
- F. Knoeppel, K. Crane, U. Pinkall, P. Schroeder. Stripe Patterns on Surfaces. ACM Trans. Graph. 34(4), 2015.
Free for personal, academic, and research use. No warranty. Commercial use requires written permission from the author.