02a3745b67
Finding-U1 and Finding-U2 from doc/reviewer/usability-audit-2026-05-31.md.
The existing examples (example_euclidean, example_layout, example_hyper_ideal)
all used the "natural theta" pattern which makes x*=0 trivially the
equilibrium — u_v ≈ 0 everywhere, no deformation. A new user following
these examples saw solver output but not conformal geometry.
New: example_flatten.cpp
- PRIMARY USE CASE: conformally flatten a mesh to the plane
- Sets Θ_v = 2π for all interior vertices (flat target)
- Pins boundary vertices (no Gauss-Bonnet check for open meshes)
- Demonstrates non-trivial u_v (cathead.obj: range ≈ 2.96, 5 Newton iters)
- Documents the difference from "natural theta" explicitly
New: example_cgal_api.cpp
- Demonstrates CGAL::discrete_conformal_map_euclidean (Discrete_conformal_map.h)
- First runnable CGAL public API example; contrast with internal API
- Documents the "natural theta" default behaviour and explains why u_v=0
- Explains when to use CGAL API vs internal API
Both examples registered in code/examples/CMakeLists.txt and compile
cleanly with -DWITH_CGAL=ON.
Updated:
- example_euclidean.cpp: prominent "TESTING CONVENTION" warning
- example_layout.cpp: same warning on set_natural_theta helper
- doc/getting-started.md: example_flatten is now the recommended
"start here" example; note on natural-theta behaviour added
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
211 lines
6.2 KiB
Markdown
211 lines
6.2 KiB
Markdown
# Getting Started
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## Prerequisites
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| Tool | Minimum | Notes |
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|---|---|---|
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| C++ compiler (GCC or Clang) | C++17 | GCC 11+ or Clang 14+ recommended |
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| CMake | 3.20 | |
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| Boost headers | 1.70 | Only for `-DWITH_CGAL_TESTS=ON` or `-DWITH_CGAL=ON` |
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| Wayland/X11 dev headers | — | Only for `-DWITH_CGAL=ON` (viewer) |
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All other dependencies (Eigen 3.4, CGAL 6.1.1, libigl 2.6, GLFW 3.4, GTest 1.14)
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are bundled as tarballs in `code/deps/tarballs/` and extracted automatically at CMake
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configure time. No internet access is required at build time (except GTest, fetched via
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`FetchContent` from GitHub).
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Install Boost on your system:
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```bash
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# Ubuntu / Debian
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apt install libboost-dev
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# macOS
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brew install boost
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```
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---
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## Clone
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```bash
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git clone https://codeberg.org/TMoussa/ConformalLabpp
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cd ConformalLabpp
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```
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---
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## Build modes
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Three modes with increasing dependencies:
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### Mode 1 — Fast tests (default, no system dependencies)
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Pure-math tests: Clausen functions, hyper-ideal geometry, matrix utilities.
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```bash
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cmake -S code -B build
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cmake --build build --target conformallab_tests -j$(nproc)
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ctest --test-dir build --output-on-failure
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```
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Expected: all pure-math tests pass (count: [`doc/api/tests.md`](api/tests.md)).
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### Mode 2 — CGAL tests, headless (recommended for CI and development)
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Full CGAL test suite. Requires Boost headers only — no display, no Wayland, no GLFW.
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```bash
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cmake -S code -B build -DWITH_CGAL_TESTS=ON
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cmake --build build --target conformallab_cgal_tests -j$(nproc)
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ctest --test-dir build -R "^cgal\." --output-on-failure
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```
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Expected: all CGAL tests pass, 0 skipped (count: [`doc/api/tests.md`](api/tests.md)).
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### Mode 3 — Full local build (CLI app + interactive viewer)
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Requires Wayland or X11 development packages (`wayland-scanner`, `libx11-dev`, etc.).
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Automatically enables the viewer library (GLFW + libigl).
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```bash
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cmake -S code -B build -DWITH_CGAL=ON
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cmake --build build -j$(nproc)
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```
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> **Note:** `-DWITH_CGAL=ON` implies `-DWITH_VIEWER=ON`. Do not use this in headless
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> environments — it will fail with `Failed to find wayland-scanner`.
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---
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## Running a single test
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```bash
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# By GTest filter (fastest, full output)
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./build/conformallab_cgal_tests --gtest_filter="NewtonSolver*"
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./build/conformallab_tests --gtest_filter="Clausen*"
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# By CTest regex
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ctest --test-dir build -R "cgal.NewtonSolver" --output-on-failure
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```
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All CGAL tests have the prefix `cgal.` in CTest (set in `tests/cgal/CMakeLists.txt`
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via `TEST_PREFIX "cgal."`).
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---
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## First run — CLI app
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After a full build (`-DWITH_CGAL=ON`):
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```bash
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# Euclidean conformal layout
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./bin/conformallab_core -i input.off -g euclidean -o layout.off -j result.json
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# Spherical layout
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./bin/conformallab_core -i input.off -g spherical -o sphere.off
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# Hyperbolic layout (HyperIdeal)
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./bin/conformallab_core -i input.off -g hyper_ideal -o hyperbolic.off
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# Show input mesh in interactive viewer
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./bin/conformallab_core -i input.off -s
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# All options
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./bin/conformallab_core --help
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```
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## Example programs
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```bash
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# PRIMARY USE CASE: conformally flatten a mesh to the plane
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./build/examples/example_flatten code/data/obj/cathead.obj flat.off
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# → non-trivial u_v (e.g. range ≈ 2.96), real conformal deformation
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# CGAL public API: one-call interface (natural theta by default)
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./build/examples/example_cgal_api [input.off]
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# Full pipeline with JSON/XML serialisation and round-trip test
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./build/examples/example_layout [input.off] [layout.off] [result.json]
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# Solver test (natural theta — u_v ≈ 0, used for pipeline validation)
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./build/examples/example_euclidean [input.off] [output.off]
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# Hyper-ideal (hyperbolic) functional
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./build/examples/example_hyper_ideal [input.off] [output.off]
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# Interactive viewer (requires WITH_VIEWER)
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./build/examples/example_viewer [input.off]
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```
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**Start here:** `example_flatten.cpp` shows the primary use case — real conformal
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flattening with `Θ_v = 2π`. `example_layout.cpp` adds JSON/XML serialisation.
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> **Note on "natural theta":** `example_euclidean` and `example_layout` use the
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> "natural theta" testing trick (`Θ_v = actual angle sum at x=0`), which makes
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> `x* = 0` trivially the equilibrium. The output `u_v ≈ 0` is expected and
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> correct for a pipeline test, but means **no conformal deformation was applied**.
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> For real UV parameterisation, use `example_flatten.cpp`.
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**Expected output of `example_euclidean` on the built-in quad-strip mesh:**
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```
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[example_euclidean] No input file given — using make_quad_strip().
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[example_euclidean] Mesh: 6 vertices, 4 faces.
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[example_euclidean] DOFs: 5 (1 vertex pinned).
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[example_euclidean] Solving Newton system…
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[example_euclidean] Converged in 1 iterations. ||G||_inf = 0
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[example_euclidean] Per-vertex conformal factors u_i:
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v0 u = 0 (pinned)
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v1 u = -1.38778e-17 ← ≈ 0 (machine epsilon)
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...
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[example_euclidean] Mesh saved to: /tmp/conformallab_euclidean_out.off
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```
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Convergence in 1 iteration is expected: the "natural equilibrium" construction
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sets x* = 0, so a small perturbation (-0.05) needs only one Newton step.
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**Quick automated start (no interactive build needed):**
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```bash
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bash scripts/try_it.sh
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```
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This clones nothing (run from inside the repo), builds the CGAL test suite, runs
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the full test suite, and prints a summary. See `scripts/try_it.sh` for details.
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---
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## Known issues
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### macOS Finder duplicates
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macOS Finder sometimes creates duplicate files named `foo 2.hpp` when copying
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the repository. These cause confusing compile errors ("redefinition of …").
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**Fix (run once from the repo root):**
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```bash
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find code/include -name "* 2.*" -delete
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find code/include -name "*\ 2.*" -delete
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```
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Files without a ` 2` suffix are always canonical — the duplicates are safe to delete.
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### First build is slow
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The first CMake configure extracts four tarballs (Eigen 3.4, CGAL 6.1.1,
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libigl 2.6, GLFW 3.4) and downloads GTest via `FetchContent`.
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Allow **30–90 seconds** for the first configure. Subsequent builds are fast
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(< 10 s incremental).
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---
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## Rebuilding the CI Docker image
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The CI runner is a self-hosted Raspberry Pi (ARM64). After changes to
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`.gitea/docker/Dockerfile.ci-cpp`:
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```bash
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docker buildx build \
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--platform linux/arm64 \
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-f .gitea/docker/Dockerfile.ci-cpp \
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-t git.eulernest.eu/conformallab/ci-cpp:latest \
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--push \
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.gitea/docker/
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```
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