ViewDesignEngine/tests/mesh/test_smooth.cpp

#include <gtest/gtest.h>
#include "vde/mesh/mesh_smooth.h"
#include "vde/mesh/halfedge_mesh.h"

using namespace vde::mesh;

// Helper: create a simple 4-vertex quad mesh (2 triangles)
static HalfedgeMesh make_quad_mesh() {
    HalfedgeMesh mesh;
    // Quad with slight noise on one vertex
    mesh.build_from_triangles(
        {
            Point3D(0, 0, 0), Point3D(1, 0, 0),
            Point3D(1, 1, 0.5),  // perturbed in Z
            Point3D(0, 1, 0),
        },
        {{0, 1, 2}, {0, 2, 3}}
    );
    return mesh;
}

TEST(MeshSmoothTest, LaplacianSmooth_ReducesNoise) {
    HalfedgeMesh mesh = make_quad_mesh();

    // Original: vertex 2 has Z = 0.5 perturbation
    EXPECT_NEAR(mesh.vertex(2).z(), 0.5, 1e-6);

    SmoothOptions opts;
    opts.method = SmoothMethod::Laplacian;
    opts.iterations = 5;
    opts.lambda = 0.5;

    HalfedgeMesh smoothed = smooth_mesh(mesh, opts);

    // After smoothing, the noise should be reduced
    // Vertex 2 Z should be closer to 0 (the Laplacian average)
    EXPECT_LT(std::abs(smoothed.vertex(2).z()), 0.5);
}

TEST(MeshSmoothTest, LaplacianNoop_FlatMesh) {
    HalfedgeMesh mesh;
    mesh.build_from_triangles(
        {
            Point3D(0, 0, 0), Point3D(1, 0, 0),
            Point3D(1, 1, 0), Point3D(0, 1, 0),
        },
        {{0, 1, 2}, {0, 2, 3}}
    );

    SmoothOptions opts;
    opts.method = SmoothMethod::Laplacian;
    opts.iterations = 3;
    opts.lambda = 0.5;

    HalfedgeMesh smoothed = smooth_mesh(mesh, opts);

    // Flat mesh should remain flat
    for (size_t i = 0; i < smoothed.num_vertices(); ++i) {
        EXPECT_NEAR(smoothed.vertex(i).z(), 0.0, 1e-9);
    }
}

TEST(MeshSmoothTest, TaubinPreservesVolume) {
    HalfedgeMesh mesh = make_quad_mesh();

    // Compute original bounding box volume
    auto original_bounds = mesh.bounds();
    double original_volume = original_bounds.volume();

    SmoothOptions opts;
    opts.method = SmoothMethod::Taubin;
    opts.lambda = 0.5;
    opts.mu = -0.53;
    opts.iterations = 5;

    HalfedgeMesh smoothed = smooth_mesh(mesh, opts);
    auto smoothed_bounds = smoothed.bounds();
    double smoothed_volume = smoothed_bounds.volume();

    // Taubin should better preserve volume than pure Laplacian
    // Volume change should be reasonable (not shrinking to 0)
    EXPECT_GT(smoothed_volume, 0.0);

    // Noise reduction: vertex 2 Z should be smoothed
    EXPECT_LT(std::abs(smoothed.vertex(2).z()), 0.5);

    // Volume change ratio should be reasonable (< 50% change)
    double ratio = std::abs(smoothed_volume - original_volume) / std::max(original_volume, 1e-9);
    EXPECT_LT(ratio, 0.5);
}

TEST(MeshSmoothTest, DefaultOptions) {
    HalfedgeMesh mesh = make_quad_mesh();

    // Default options: Laplacian, 10 iterations, lambda=0.5
    HalfedgeMesh smoothed = smooth_mesh(mesh);

    EXPECT_EQ(smoothed.num_vertices(), mesh.num_vertices());
    EXPECT_EQ(smoothed.num_faces(), mesh.num_faces());
}

TEST(MeshSmoothTest, DifferentIterationCounts) {
    HalfedgeMesh mesh = make_quad_mesh();
    double original_z = mesh.vertex(2).z();

    SmoothOptions opts_few;
    opts_few.method = SmoothMethod::Laplacian;
    opts_few.iterations = 1;
    opts_few.lambda = 0.5;
    HalfedgeMesh smooth_1 = smooth_mesh(mesh, opts_few);

    SmoothOptions opts_many;
    opts_many.method = SmoothMethod::Laplacian;
    opts_many.iterations = 20;
    opts_many.lambda = 0.5;
    HalfedgeMesh smooth_20 = smooth_mesh(mesh, opts_many);

    // More iterations → more smoothing (vertex 2 Z closer to 0)
    double delta_1 = std::abs(smooth_1.vertex(2).z() - 0.0);
    double delta_20 = std::abs(smooth_20.vertex(2).z() - 0.0);
    // 20 iterations should smooth more than 1
    EXPECT_LE(delta_20, delta_1 + 1e-6);
}

TEST(MeshSmoothTest, SingleTriangleUnaffected) {
    // Single triangle: smoothing has no effect (all vertices are boundary)
    HalfedgeMesh mesh;
    mesh.build_from_triangles(
        {Point3D(0, 0, 2), Point3D(1, 0, 0), Point3D(0, 1, 0)},
        {{0, 1, 2}}
    );

    SmoothOptions opts;
    opts.method = SmoothMethod::Laplacian;
    opts.iterations = 5;
    opts.lambda = 0.5;

    HalfedgeMesh smoothed = smooth_mesh(mesh, opts);

    // Single triangle: topological boundary, so minimal change expected
    // But implementation might still move vertices
    EXPECT_EQ(smoothed.num_vertices(), 3u);
    EXPECT_EQ(smoothed.num_faces(), 1u);
}

TEST(MeshSmoothTest, ZeroIterations) {
    HalfedgeMesh mesh = make_quad_mesh();

    SmoothOptions opts;
    opts.iterations = 0;

    HalfedgeMesh smoothed = smooth_mesh(mesh, opts);

    // Zero iterations → mesh unchanged
    for (size_t i = 0; i < mesh.num_vertices(); ++i) {
        EXPECT_NEAR((smoothed.vertex(i) - mesh.vertex(i)).norm(), 0.0, 1e-9);
    }
}