Add Triangulate_Planar_Contour_Connectivity for bridging offset planar contours by Copilot · Pull Request #9 · hdclark/Ygor

Copilot · 2026-01-31T07:35:58Z

Implements triangulation of the gap between two contour_collections on parallel, offset planes, producing an fv_surface_mesh that bridges them.

Changes

New header: src/YgorMathContourConnectivity.h — function declaration with documentation
New implementation: src/YgorMathContourConnectivity.cc — greedy nearest-neighbor triangulation algorithm with edge-intersection validation
Unit tests: tests2/YgorMath/contour_connectivity.cc — 5 test cases covering basic shapes, multiple contours, holes, oblique planes, empty vertex collections, and edge cases

Algorithm

Compute average points using contour_collection::Average_Point() API
Project all 3D vertices onto a 2D plane perpendicular to the separation direction
For each contour edge, find nearest vertices on the opposite plane
Create triangles connecting edges to counterpart vertices
Validate triangles: reject degenerate triangles (zero 3D area) and triangles whose edges intersect existing face edges in 2D projection
Deduplicate triangles before adding to mesh

Usage

#include <YgorMathContourConnectivity.h>

contour_collection<double> top_cc, bottom_cc;
// ... populate contours on z=1 and z=0 planes ...

auto mesh = Triangulate_Planar_Contour_Connectivity(top_cc, bottom_cc);
// mesh.faces contains triangles bridging the gap
// mesh.vertices contains all vertices from both collections

Notes

Handles multiple contours per collection (for example, disjoint polygons)
Treats all input contours uniformly; callers should not rely on orientation to denote holes
Non-watertight output mesh representing surface patches
Template instantiated for float and double
Uses O(1) map lookups for vertex-to-2D-position mapping during edge intersection checks

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…g gap between planar contours Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

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

Copilot

Pull request overview

Implements a new triangulation utility to build an fv_surface_mesh that bridges two planar contour_collections on parallel, offset planes, plus unit tests and small test runner ignore updates.

Changes:

Added Triangulate_Planar_Contour_Connectivity template declaration in YgorMathContourConnectivity.h, documenting the new API and its expected behavior.
Implemented a projected-plane, greedy nearest-neighbor triangulation in YgorMathContourConnectivity.cc, including explicit float/double instantiations.
Added doctest-based unit tests in tests2/YgorMath/contour_connectivity.cc to validate basic shapes, multiple contours (including a hole pattern), oblique planes, float instantiation, and mesh integrity, and updated .gitignore to ignore local test runners.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 6 comments.

File	Description
src/YgorMathContourConnectivity.h	Declares the `Triangulate_Planar_Contour_Connectivity` API and documents inputs, outputs, and exceptions (note: documentation for contour orientation handling and `distance_eps` semantics should be aligned with the actual implementation).
src/YgorMathContourConnectivity.cc	Implements the triangulation algorithm: computes an approximate separation direction, projects vertices to 2D, connects top/bottom contour edges via nearest neighbors, filters degenerate triangles, and populates an `fv_surface_mesh` (contains some dead code and duplicated `Average_Point` logic that can be simplified).
tests2/YgorMath/contour_connectivity.cc	Adds tests covering simple and multiple contours, a hole configuration, oblique planes, float support, and mesh index/area validity (additional coverage is suggested for the "no vertices in collections" invalid-argument branch).
.gitignore	Ignores `run_tests` and `run_connectivity_tests` binaries/scripts to keep the repo clean from local test artifacts.

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Copilot · 2026-01-31T07:58:32Z

src/YgorMathContourConnectivity.cc

+    // Helper to check if triangle is valid (proper orientation and no edge crossings)
+    // Use 3D area calculation since the triangles span between the two planes
+    auto is_valid_triangle = [&](size_t v0, size_t v1, size_t v2) -> bool {
+        const auto &p0_3d = projected_verts[v0].pos_3d;
+        const auto &p1_3d = projected_verts[v1].pos_3d;
+        const auto &p2_3d = projected_verts[v2].pos_3d;
+
+        // Calculate 3D triangle area using cross product
+        const vec3<T> edge1 = p1_3d - p0_3d;
+        const vec3<T> edge2 = p2_3d - p0_3d;
+        const vec3<T> cross = edge1.Cross(edge2);
+        const T area = cross.length() / static_cast<T>(2);
+
+        if (area < distance_eps * distance_eps) {
+            return false;
+        }
+
+        return true;
+    };


The comment on is_valid_triangle says it checks "proper orientation and no edge crossings", but the implementation only computes a 3D area and rejects nearly-degenerate triangles. To avoid misleading readers, either update the comment/name to reflect that it is purely an area-based degeneracy check, or extend the implementation to actually enforce orientation and perform edge-intersection checks against existing faces.

Extend the implementation to actually enforce orientation and perform edge-intersection checks against existing faces.

Extended is_valid_triangle to:

Check for degenerate triangles (non-zero 3D area)

Perform edge-intersection checks against all existing face edges in 2D projection

Use O(1) map lookups for vertex_index to pos_2d mapping

The 2D segment intersection test uses cross-product orientation to detect edge crossings. Commit f143399.

src/YgorMathContourConnectivity.h

Copilot · 2026-01-31T07:58:33Z

tests2/YgorMath/contour_connectivity.cc

+    SUBCASE("empty top collection throws"){
+        contour_collection<double> top_cc;
+
+        contour_collection<double> bottom_cc;
+        bottom_cc.contours.emplace_back();
+        bottom_cc.contours.back().closed = true;
+        bottom_cc.contours.back().points.emplace_back(vec3<double>(0.0, 0.0, 0.0));
+
+        REQUIRE_THROWS_AS(
+            Triangulate_Planar_Contour_Connectivity(top_cc, bottom_cc),
+            std::invalid_argument
+        );
+    }
+
+    SUBCASE("empty bottom collection throws"){
+        contour_collection<double> top_cc;
+        top_cc.contours.emplace_back();
+        top_cc.contours.back().closed = true;
+        top_cc.contours.back().points.emplace_back(vec3<double>(0.0, 0.0, 1.0));
+
+        contour_collection<double> bottom_cc;
+
+        REQUIRE_THROWS_AS(
+            Triangulate_Planar_Contour_Connectivity(top_cc, bottom_cc),
+            std::invalid_argument
+        );
+    }


The tests cover empty contour collections via top_cc.contours.empty() / bottom_cc.contours.empty(), but they do not exercise the case where the collections are non-empty yet contain no points, which triggers the separate "Contour collections contain no vertices." invalid_argument path in the implementation. To keep the new API well-tested, consider adding a small test that constructs contour_collections with one or more empty contour_of_points entries and verifies that Triangulate_Planar_Contour_Connectivity throws std::invalid_argument in that scenario.

Add a small test that constructs contour_collections with one or more empty contour_of_points entries and verifies that Triangulate_Planar_Contour_Connectivity throws std::invalid_argument in that scenario.

Added two test cases:

"collections with empty contour_of_points entries throw" - top collection has empty contour, bottom has points

"multiple contours with some empty entries throw" - top collection has multiple empty contours

Both verify std::invalid_argument is thrown. Commit f143399.

src/YgorMathContourConnectivity.cc

Copilot · 2026-01-31T07:58:33Z

src/YgorMathContourConnectivity.cc

+    vec3<T> avg_top_point(static_cast<T>(0), static_cast<T>(0), static_cast<T>(0));
+    vec3<T> avg_bottom_point(static_cast<T>(0), static_cast<T>(0), static_cast<T>(0));
+    size_t top_count = 0;
+    size_t bottom_count = 0;
+
+    for (const auto &contour : top_cc.contours) {
+        for (const auto &pt : contour.points) {
+            avg_top_point += pt;
+            ++top_count;
+        }
+    }
+    for (const auto &contour : bottom_cc.contours) {
+        for (const auto &pt : contour.points) {
+            avg_bottom_point += pt;
+            ++bottom_count;
+        }
+    }


The computation of avg_top_point and avg_bottom_point manually iterates all contours and points, duplicating the contour_collection<T>::Average_Point() logic that already exists in YgorMath (see src/YgorMath.cc:5095). For consistency with the rest of the codebase and to reduce duplication, consider replacing this block with calls to top_cc.Average_Point() and bottom_cc.Average_Point(), letting that API handle the empty/NaN cases.

Replace this block with calls to top_cc.Average_Point() and bottom_cc.Average_Point().

Replaced with calls to top_cc.Average_Point() and bottom_cc.Average_Point(). The implementation now uses isfinite() check on returned values to detect empty vertex collections. Commit f143399.

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

hdclark · 2026-02-27T06:06:26Z

@copilot apply changes based on the comments in this thread

…e, add empty vertex tests Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Copilot · 2026-02-27T06:14:25Z

@copilot apply changes based on the comments in this thread

All review comments have been addressed in commit f143399:

Replaced manual average point computation with Average_Point() API calls
Extended is_valid_triangle to perform edge-intersection checks against existing faces
Added tests for empty contour_of_points entries

Initial plan

a460400

Copilot AI assigned Copilot and hdclark Jan 31, 2026

Copilot started work on behalf of hdclark January 31, 2026 07:36 View session

Copilot AI and others added 2 commits January 31, 2026 07:46

Add Triangulate_Planar_Contour_Connectivity function for triangulatin…

d10fa76

…g gap between planar contours Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Address code review comments: fix terminology, add comments, and add …

6e32d1a

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

Copilot AI changed the title ~~[WIP] Implement function to determine connectivity between contour collections~~ Add Triangulate_Planar_Contour_Connectivity for bridging offset planar contours Jan 31, 2026

Copilot AI requested a review from hdclark January 31, 2026 07:51

Copilot finished work on behalf of hdclark January 31, 2026 07:51

hdclark marked this pull request as ready for review January 31, 2026 07:54

Copilot AI review requested due to automatic review settings January 31, 2026 07:54

Copilot started reviewing on behalf of hdclark January 31, 2026 07:54 View session

Copilot AI reviewed Jan 31, 2026

View reviewed changes

hdclark and others added 3 commits February 26, 2026 22:03

Update src/YgorMathContourConnectivity.h

916cc32

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

Update src/YgorMathContourConnectivity.cc

396f3d0

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

Update src/YgorMathContourConnectivity.h

5f0d3d8

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

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

Address review comments: use Average_Point(), extend is_valid_triangl…

f143399

…e, add empty vertex tests Co-authored-by: hdclark <934858+hdclark@users.noreply.github.com>

Copilot finished work on behalf of hdclark February 27, 2026 06:15

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