Add Triangulate_Contours for planar polygon triangulation by Copilot · Pull Request #8 · hdclark/Ygor

Copilot · 2026-01-31T07:09:10Z

Implements polygon triangulation for contour_collection vertices projected onto a best-fit plane, returning an fv_surface_mesh with triangles as faces.

Changes

Triangulate_Contours<T,I>(const contour_collection<T>&) — new free function in YgorMath.h/.cc
- Projects all contour vertices onto best-fit plane via Plane_Orthogonal_Regression
- Triangulates using ear-clipping algorithm (handles non-convex, non-monotone polygons)
- Uses is_ccw flag to distinguish outer contours (CCW) from holes (CW) in bridging logic
- Bridges multiple contours via nearest-point connections with visibility checks to avoid self-intersections
- Template instantiations for float/double × uint32_t/uint64_t
Unit tests in tests2/YgorMath/triangulate_contours.cc
- Covers: convex/concave shapes, tilted planes, multi-contour bridging, degenerate cases, area preservation
- Includes test for collinear points causing plane regression failure (returns empty mesh)

Usage

contour_collection<double> cc;
// ... populate contours ...

auto mesh = Triangulate_Contours<double, uint32_t>(cc);
// mesh.vertices: projected 3D points on best-fit plane
// mesh.faces: triangle indices (n-2 triangles for n-gon)

Resulting mesh is a non-watertight surface patch as specified.

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…nd add unit tests Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Copilot

Pull request overview

This PR adds a Triangulate_Contours<T,I> utility that projects a contour_collection onto a best-fit plane and triangulates it into an fv_surface_mesh, along with a focused unit test suite validating the new behavior.

Changes:

Declare and implement Triangulate_Contours<T,I>(const contour_collection<T>&) in YgorMath.h/.cc, including explicit template instantiations for {float,double} × {uint32_t,uint64_t}.
Implement an ear-clipping based triangulation on a best-fit plane with support for multiple contours via a bridging heuristic.
Add tests2/YgorMath/triangulate_contours.cc covering basic polygons, concave shapes, tilted planes, multiple contours, degeneracies, and different scalar/index types.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/YgorMath.h	Declares the `Triangulate_Contours` template and documents its intended behavior and assumptions.
src/YgorMath.cc	Implements `Triangulate_Contours`, including plane fitting, 2D projection, multi-contour bridging, ear-clipping, and explicit template instantiations.
tests2/YgorMath/triangulate_contours.cc	Adds doctest-based unit tests for `Triangulate_Contours` across a variety of geometric configurations and type combinations.

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src/YgorMath.h

Copilot · 2026-01-31T07:53:56Z

src/YgorMath.cc

+    struct ContourInfo {
+        size_t start_idx;
+        size_t end_idx; // One past the last index.
+        bool is_ccw;    // Counter-clockwise orientation (outer contour) or clockwise (hole).
+    };


ContourInfo::is_ccw is computed but never used in the rest of the function, which adds noise and suggests orientation‑dependent logic that is not actually implemented. Either remove this field and the associated area computation, or use it to distinguish outer contours from holes in the bridging logic so the stored flag has a purpose.

Use it to distinguish outer contours from holes in the bridging logic so the stored flag has a purpose.

Updated the bridging logic to use is_ccw to distinguish outer contours from holes. The sorting now prioritizes outer contours (CCW) first before processing holes (CW), ensuring outer boundaries are established before holes are merged in. See commit d25f924.

src/YgorMath.cc

Copilot · 2026-01-31T07:53:56Z

src/YgorMath.cc

+    try {
+        best_fit_plane = Plane_Orthogonal_Regression(all_points);
+    } catch(const std::exception &) {
+        // Points are likely collinear; cannot triangulate.
+        return mesh;


This catch block returns an empty mesh when Plane_Orthogonal_Regression throws (e.g., for collinear input), but there is no unit test exercising this failure path. Given the rest of the function is well covered by tests, consider adding a test case with collinear contour points to confirm the intended "empty mesh on regression failure" behaviour and guard against regressions.

Implement this suggestion.

Added a test case "collinear points cause plane regression failure and return empty mesh" that verifies the empty mesh behavior when Plane_Orthogonal_Regression throws due to collinear input. See commit d25f924.

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

hdclark · 2026-02-27T06:01:11Z

@copilot apply changes based on the comments in this thread

…ollinear points test Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Copilot · 2026-02-27T06:06:53Z

@copilot apply changes based on the comments in this thread

Applied all changes from the review thread in commit d25f924:

Updated the bridging logic to use is_ccw to distinguish outer contours (CCW) from holes (CW), sorting outer contours first
Added a unit test for collinear points that verifies the empty mesh behavior when plane regression fails

Initial plan

dd5365b

Copilot AI assigned Copilot and hdclark Jan 31, 2026

Copilot started work on behalf of hdclark January 31, 2026 07:09 View session

Copilot AI and others added 2 commits January 31, 2026 07:17

Implement Triangulate_Contours function with ear-clipping algorithm a…

e221fb8

…nd add unit tests Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Address code review: extract epsilon constant with descriptive comment

12a95b5

Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Implement polygon triangulation algorithm for vertices~~ Add Triangulate_Contours for planar polygon triangulation Jan 31, 2026

Copilot AI requested a review from hdclark January 31, 2026 07:22

Copilot finished work on behalf of hdclark January 31, 2026 07:22

hdclark marked this pull request as ready for review January 31, 2026 07:49

Copilot AI review requested due to automatic review settings January 31, 2026 07:49

Copilot started reviewing on behalf of hdclark January 31, 2026 07:49 View session

Copilot AI reviewed Jan 31, 2026

View reviewed changes

hdclark and others added 2 commits February 26, 2026 21:58

Update src/YgorMath.h

1026870

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Update src/YgorMath.cc

f6bef54

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Copilot started work on behalf of hdclark February 27, 2026 06:01 View session

Address review: use is_ccw to distinguish outer/inner contours, add c…

d25f924

…ollinear points test Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Copilot finished work on behalf of hdclark February 27, 2026 06:08

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Add Triangulate_Contours for planar polygon triangulation#8

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