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OrcaSlicer/tests/libslic3r/test_texture_displacement.cpp

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#define NOMINMAX
#include <catch2/catch_all.hpp>
#include <algorithm>
#include <cmath>
#include <fstream>
#include <limits>
#include <boost/filesystem.hpp>
#include "libslic3r/TextureDisplacement.hpp"
#include "libslic3r/TriangleMesh.hpp"
#include "libslic3r/TriangleSelector.hpp"
#include "libslic3r/PNGReadWrite.hpp"
using namespace Slic3r;
using Catch::Matchers::WithinAbs;
// Encodes a flat (uniform-value) grayscale image through Slic3r's own PNG writer/reader round
// trip, so decode_height_texture() (which only accepts true 8-bit grayscale PNG) is guaranteed a
// compatible file, exactly like the GUI's "Add texture" import path does.
static std::shared_ptr<std::vector<unsigned char>> make_flat_gray_png(uint8_t value, size_t w = 4, size_t h = 4)
{
std::vector<uint8_t> pixels(w * h, value);
const boost::filesystem::path tmp_path = boost::filesystem::temp_directory_path()
/ boost::filesystem::unique_path("texdisp_test_%%%%%%%%.png");
REQUIRE(Slic3r::png::write_gray_to_file(tmp_path.string(), w, h, pixels));
std::vector<unsigned char> bytes;
{
std::ifstream ifs(tmp_path.string(), std::ios::binary);
bytes.assign(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
}
boost::system::error_code ec;
boost::filesystem::remove(tmp_path, ec);
REQUIRE_FALSE(bytes.empty());
return std::make_shared<std::vector<unsigned char>>(std::move(bytes));
}
// A hard-edged black/white checkerboard, the worst case for a height map: every texel boundary is a
// step, which is precisely the relief the post-process smoothing exists to round off.
static std::shared_ptr<std::vector<unsigned char>> make_checkerboard_png(size_t w = 16, size_t h = 16)
{
std::vector<uint8_t> pixels(w * h);
for (size_t y = 0; y < h; ++y)
for (size_t x = 0; x < w; ++x)
pixels[y * w + x] = ((x / 2 + y / 2) % 2) ? 255 : 0;
const boost::filesystem::path tmp_path = boost::filesystem::temp_directory_path()
/ boost::filesystem::unique_path("texdisp_test_%%%%%%%%.png");
REQUIRE(Slic3r::png::write_gray_to_file(tmp_path.string(), w, h, pixels));
std::vector<unsigned char> bytes;
{
std::ifstream ifs(tmp_path.string(), std::ios::binary);
bytes.assign(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
}
boost::system::error_code ec;
boost::filesystem::remove(tmp_path, ec);
REQUIRE_FALSE(bytes.empty());
return std::make_shared<std::vector<unsigned char>>(std::move(bytes));
}
TEST_CASE("TextureDisplacement: decode_height_texture round-trips an 8-bit grayscale PNG", "[TextureDisplacement]")
{
TextureDisplacementLayer layer;
layer.image_data = make_flat_gray_png(128, 4, 4);
DecodedHeightTexture tex = decode_height_texture(layer);
REQUIRE_FALSE(tex.empty());
CHECK(tex.width == 4);
CHECK(tex.height == 4);
REQUIRE_THAT(tex.sample(Vec2f(0.5f, 0.5f)), WithinAbs(128.0 / 255.0, 1.0 / 255.0));
}
TEST_CASE("TextureDisplacement: an empty layer list leaves the mesh unchanged", "[TextureDisplacement]")
{
const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
const std::vector<TextureDisplacementLayer> layers; // none
TextureDisplacementFacetsData facets{}; // all empty
const indexed_triangle_set result = build_texture_displacement(cube, layers, facets);
REQUIRE(result.vertices.size() == cube.vertices.size());
REQUIRE(result.indices.size() == cube.indices.size());
for (size_t i = 0; i < cube.vertices.size(); ++i)
for (int c = 0; c < 3; ++c)
CHECK(result.vertices[i](c) == cube.vertices[i](c));
}
TEST_CASE("TextureDisplacement: fully painting a mesh displaces every vertex along its own normal", "[TextureDisplacement]")
{
const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
const TriangleMesh cube_mesh(cube);
TriangleSelector selector(cube_mesh);
for (int f = 0; f < int(cube.indices.size()); ++f)
selector.set_facet(f, EnforcerBlockerType::ENFORCER);
TextureDisplacementFacetsData facets{};
facets[0] = selector.serialize();
TextureDisplacementLayer layer;
layer.slot = 0;
layer.depth_mm = 2.0f;
layer.tiling_scale = 5.0f;
layer.image_data = make_flat_gray_png(255); // sample() == 1.0 everywhere -> full depth_mm displacement
const indexed_triangle_set result = build_texture_displacement(cube, {layer}, facets);
REQUIRE(result.vertices.size() == cube.vertices.size());
for (size_t i = 0; i < cube.vertices.size(); ++i) {
const float moved = (result.vertices[i] - cube.vertices[i]).norm();
CHECK_THAT(moved, WithinAbs(layer.depth_mm, 1e-3f));
}
}
// Paints every facet of `mesh` into a serialized mask, the way "Select whole model" does.
static TriangleSelector::TriangleSplittingData paint_whole_mesh(const indexed_triangle_set &mesh)
{
const TriangleMesh tm(mesh);
TriangleSelector selector(tm);
for (int f = 0; f < int(mesh.indices.size()); ++f)
selector.set_facet(f, EnforcerBlockerType::ENFORCER);
return selector.serialize();
}
// Regression test for the bug this feature shipped with: with two layers painted over the same
// area, the second one was silently dropped (its paint mask was remapped onto the mesh the first
// layer had already displaced, which routinely produced an empty bitstream). Every layer is now
// evaluated against the original mesh instead, so both must show up in the total.
TEST_CASE("TextureDisplacement: a second layer over the same area is applied too", "[TextureDisplacement]")
{
const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
TextureDisplacementFacetsData facets{};
facets[0] = paint_whole_mesh(cube);
facets[1] = facets[0]; // both layers cover the whole cube
TextureDisplacementLayer base;
base.slot = 0;
base.depth_mm = 1.0f;
base.tiling_scale = 5.0f;
base.image_data = make_flat_gray_png(255); // height 1.0 everywhere
TextureDisplacementLayer second = base;
second.slot = 1;
second.depth_mm = 0.5f;
second.blend_mode = TextureBlendMode::Add;
const indexed_triangle_set result = build_texture_displacement(cube, {base, second}, facets);
// Topology is preserved exactly, so vertices can be compared 1:1 with the input.
REQUIRE(result.vertices.size() == cube.vertices.size());
REQUIRE(result.indices.size() == cube.indices.size());
for (size_t i = 0; i < cube.vertices.size(); ++i)
CHECK_THAT((result.vertices[i] - cube.vertices[i]).norm(), WithinAbs(1.5f, 1e-3f)); // 1.0 + 0.5, not just 1.0
}
TEST_CASE("TextureDisplacement: blend modes combine a layer with the ones below it", "[TextureDisplacement]")
{
const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
TextureDisplacementFacetsData facets{};
facets[0] = paint_whole_mesh(cube);
facets[1] = facets[0];
TextureDisplacementLayer base;
base.slot = 0;
base.depth_mm = 2.0f;
base.tiling_scale = 5.0f;
base.image_data = make_flat_gray_png(255); // -> contributes exactly +2.0 mm
TextureDisplacementLayer second = base;
second.slot = 1;
second.depth_mm = 0.5f; // -> its own value is 0.5 mm
// Expected total displacement for each mode, given base = 2.0 mm and second = 0.5 mm. Multiply
// and Divide treat the layer's value as a factor relative to 1 mm (see TextureBlendMode).
const auto expected = GENERATE(table<TextureBlendMode, float>({
{ TextureBlendMode::Add, 2.5f }, // 2.0 + 0.5
{ TextureBlendMode::Subtract, 1.5f }, // 2.0 - 0.5
{ TextureBlendMode::Multiply, 1.0f }, // 2.0 * 0.5
{ TextureBlendMode::Divide, 4.0f }, // 2.0 / 0.5
}));
second.blend_mode = std::get<0>(expected);
const indexed_triangle_set result = build_texture_displacement(cube, {base, second}, facets);
REQUIRE(result.vertices.size() == cube.vertices.size());
for (size_t i = 0; i < cube.vertices.size(); ++i)
CHECK_THAT((result.vertices[i] - cube.vertices[i]).norm(), WithinAbs(std::get<1>(expected), 1e-3f));
}
TEST_CASE("TextureDisplacement: the lowest layer ignores its blend mode", "[TextureDisplacement]")
{
// Multiply against the implicit zero base would annihilate the only layer present; the first
// layer to reach a vertex always starts the total off additively instead.
const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
TextureDisplacementFacetsData facets{};
facets[0] = paint_whole_mesh(cube);
TextureDisplacementLayer layer;
layer.slot = 0;
layer.depth_mm = 2.0f;
layer.tiling_scale = 5.0f;
layer.blend_mode = TextureBlendMode::Multiply;
layer.image_data = make_flat_gray_png(255);
const indexed_triangle_set result = build_texture_displacement(cube, {layer}, facets);
for (size_t i = 0; i < cube.vertices.size(); ++i)
CHECK_THAT((result.vertices[i] - cube.vertices[i]).norm(), WithinAbs(2.0f, 1e-3f));
}
TEST_CASE("TextureDisplacement: the patch border is displaced by default and pinned on request", "[TextureDisplacement]")
{
// A small triangle fan around a central vertex O, with 4 outer points A/B/C/D forming 4
// triangles T0..T3 in the XY plane. Only T0, T1, T2 are painted, T3 is left unpainted, so:
// O: touches all 4 triangles (incl. unpainted T3) -> patch border
// A: touches T0 (painted) and T3 (unpainted) -> patch border
// D: touches T2 (painted) and T3 (unpainted) -> patch border
// B: touches only T0 and T1 (both painted) -> interior
// C: touches only T1 and T2 (both painted) -> interior
indexed_triangle_set fan;
fan.vertices = { {0.f, 0.f, 0.f}, {1.f, 0.f, 0.f}, {0.f, 1.f, 0.f}, {-1.f, 0.f, 0.f}, {0.f, -1.f, 0.f} };
fan.indices = { {0, 1, 2}, {0, 2, 3}, {0, 3, 4}, {0, 4, 1} };
const TriangleMesh fan_mesh(fan);
TriangleSelector selector(fan_mesh);
selector.set_facet(0, EnforcerBlockerType::ENFORCER);
selector.set_facet(1, EnforcerBlockerType::ENFORCER);
selector.set_facet(2, EnforcerBlockerType::ENFORCER);
// facet 3 (T3) is left at its default EnforcerBlockerType::NONE.
TextureDisplacementFacetsData facets{};
facets[0] = selector.serialize();
TextureDisplacementLayer layer;
layer.slot = 0;
layer.depth_mm = 1.0f;
layer.tiling_scale = 5.0f;
layer.image_data = make_flat_gray_png(255);
// The bake is topology-preserving, so it only ever moves fan's own vertices, in order.
auto moved = [&](const indexed_triangle_set &result, size_t i) {
return (result.vertices[i] - fan.vertices[i]).norm() > 1e-6f;
};
SECTION("by default the whole painted patch moves, border included")
{
const indexed_triangle_set result = build_texture_displacement(fan, {layer}, facets);
REQUIRE(result.vertices.size() == fan.vertices.size());
for (size_t i = 0; i < fan.vertices.size(); ++i)
CHECK(moved(result, i));
// ... straight along the painted surface's own normal (+Z here), by the full depth. Nothing
// has torn: the unpainted triangle T3 simply shares the moved vertices.
for (size_t i = 0; i < fan.vertices.size(); ++i)
CHECK_THAT(result.vertices[i].z() - fan.vertices[i].z(), WithinAbs(1.0f, 1e-3f));
CHECK(result.indices == fan.indices);
}
SECTION("pinning the border holds exactly the vertices an unpainted triangle also uses")
{
TextureDisplacementOptions options;
options.displace_border = false;
const indexed_triangle_set result = build_texture_displacement(fan, {layer}, facets, options);
CHECK_FALSE(moved(result, 0)); // O: border
CHECK_FALSE(moved(result, 1)); // A: border
CHECK_FALSE(moved(result, 4)); // D: border
CHECK(moved(result, 2)); // B: interior
CHECK(moved(result, 3)); // C: interior
}
}
TEST_CASE("TextureDisplacement: post-process smoothing relaxes only what moved", "[TextureDisplacement]")
{
// A checkerboard height map on a fine grid gives a relief full of hard steps - exactly what the
// smoothing pass is for. Only the central square is painted, so the patch has a real border.
indexed_triangle_set plane;
plane.vertices = { { 0.f, 0.f, 0.f }, { 20.f, 0.f, 0.f }, { 20.f, 20.f, 0.f }, { 0.f, 20.f, 0.f } };
plane.indices = { { 0, 1, 2 }, { 0, 2, 3 } };
const indexed_triangle_set grid = subdivide_mesh_uniform(plane, 1.f, 6);
REQUIRE(grid.indices.size() > 256);
std::vector<uint8_t> painted(grid.indices.size(), 0);
const TriangleMesh grid_mesh(grid);
TriangleSelector selector(grid_mesh);
for (int i = 0; i < int(grid.indices.size()); ++i) {
const auto &t = grid.indices[i];
float cx = 0.f, cy = 0.f;
for (int k = 0; k < 3; ++k) {
cx += grid.vertices[t[k]].x() / 3.f;
cy += grid.vertices[t[k]].y() / 3.f;
}
if (cx > 5.f && cx < 15.f && cy > 5.f && cy < 15.f) {
selector.set_facet(i, EnforcerBlockerType::ENFORCER);
painted[size_t(i)] = 1;
}
}
REQUIRE(std::count(painted.begin(), painted.end(), uint8_t(1)) > 32);
TextureDisplacementFacetsData facets{};
facets[0] = selector.serialize();
TextureDisplacementLayer layer;
layer.slot = 0;
layer.depth_mm = 2.0f;
layer.tiling_scale = 6.0f;
// The patch rim: vertices shared by a painted and an unpainted triangle - exactly the set
// TextureDisplacementOptions::smooth_skip_border holds out of the relaxation.
std::vector<uint8_t> rim(grid.vertices.size(), 0), inside(grid.vertices.size(), 0);
for (size_t i = 0; i < grid.indices.size(); ++i)
for (int k = 0; k < 3; ++k)
(painted[i] ? inside : rim)[size_t(grid.indices[i][k])] = 1;
size_t rim_count = 0;
for (size_t v = 0; v < rim.size(); ++v) {
rim[v] = (rim[v] && inside[v]) ? 1 : 0;
rim_count += rim[v];
}
REQUIRE(rim_count > 8);
TextureDisplacementOptions options;
options.smooth_enabled = true;
options.smooth_strength = 0.5f;
options.smooth_iterations = 4;
SECTION("it rounds off the steps without touching the topology")
{
layer.image_data = make_checkerboard_png();
// Dirichlet energy over the mesh's edges. Laplacian relaxation is gradient descent on exactly
// this, so it is the quantity guaranteed to fall - unlike the min/max spread of z, which is
// pinned by whichever vertices are held (the unpainted surface at zero, and by default the
// patch rim as well) and so need not move at all.
auto roughness = [](const indexed_triangle_set &its) {
double e = 0.0;
for (const auto &t : its.indices)
for (int k = 0; k < 3; ++k) {
const double d = double(its.vertices[t[k]].z()) - double(its.vertices[t[(k + 1) % 3]].z());
e += d * d;
}
return e;
};
const indexed_triangle_set raw = build_texture_displacement(grid, { layer }, facets);
REQUIRE(roughness(raw) > 0.0); // the checkerboard really did produce relief to smooth
const indexed_triangle_set smoothed = build_texture_displacement(grid, { layer }, facets, options);
CHECK(roughness(smoothed) < roughness(raw));
CHECK(smoothed.indices == raw.indices); // ... without touching the topology
CHECK(smoothed.vertices.size() == raw.vertices.size());
for (size_t v = 0; v < rim.size(); ++v) // ... and the held rim is bit-identical
if (rim[v])
CHECK_THAT(smoothed.vertices[v].z(), WithinAbs(raw.vertices[v].z(), 1e-6f));
}
SECTION("\"ignore outer ring\" decides whether the patch rim relaxes")
{
// A flat white texture makes this exact rather than statistical: every painted vertex is
// displaced to precisely depth_mm, so a movable interior vertex sees nothing but neighbours at
// its own height and cannot move, while every rim vertex has at least one neighbour outside the
// paint pinned at zero and so must come down the moment it is allowed to.
layer.image_data = make_flat_gray_png(255);
const indexed_triangle_set raw = build_texture_displacement(grid, { layer }, facets);
options.smooth_skip_border = true;
const indexed_triangle_set kept = build_texture_displacement(grid, { layer }, facets, options);
options.smooth_skip_border = false;
const indexed_triangle_set relaxed = build_texture_displacement(grid, { layer }, facets, options);
// Asserted on z alone, not on the whole position: relaxation averages all three coordinates,
// and while the tangential drift cancels by symmetry on a regular grid it does so only up to
// floating-point summation order, which is not something to pin down across three platforms.
// Height is what the option is about and it is exact - every neighbour of a movable vertex sits
// at the same height, so its own height cannot move.
for (size_t v = 0; v < rim.size(); ++v)
if (rim[v]) {
CHECK_THAT(kept.vertices[v].z(), WithinAbs(raw.vertices[v].z(), 1e-6f)); // held
CHECK(relaxed.vertices[v].z() < raw.vertices[v].z()); // melted down
}
}
}
TEST_CASE("TextureDisplacement: smooth_mesh_vertices holds everything outside its mask", "[TextureDisplacement]")
{
// A single spike on a flat sheet: relaxing it must pull the spike down and leave every vertex
// that is not flagged movable at exactly the coordinates it started at.
indexed_triangle_set plane;
plane.vertices = { { 0.f, 0.f, 0.f }, { 8.f, 0.f, 0.f }, { 8.f, 8.f, 0.f }, { 0.f, 8.f, 0.f } };
plane.indices = { { 0, 1, 2 }, { 0, 2, 3 } };
indexed_triangle_set grid = subdivide_mesh_uniform(plane, 1.f, 4);
// Raise one interior vertex, and let only it and its immediate neighbours move.
size_t spike = 0;
float best = std::numeric_limits<float>::max();
for (size_t i = 0; i < grid.vertices.size(); ++i)
if (const float d = (grid.vertices[i] - Vec3f(4.f, 4.f, 0.f)).norm(); d < best) {
best = d;
spike = i;
}
grid.vertices[spike].z() = 5.f;
std::vector<uint8_t> movable(grid.vertices.size(), 0);
movable[spike] = 1;
for (const auto &t : grid.indices)
for (int e = 0; e < 3; ++e)
if (size_t(t[e]) == spike)
for (int k = 0; k < 3; ++k)
movable[size_t(t[k])] = 1;
const indexed_triangle_set before = grid;
smooth_mesh_vertices(grid, movable, 0.5f, 3);
CHECK(grid.vertices[spike].z() < before.vertices[spike].z()); // the spike came down
CHECK(grid.vertices[spike].z() > 0.f); // but was not flattened outright
CHECK(grid.indices == before.indices); // topology untouched
for (size_t i = 0; i < grid.vertices.size(); ++i)
if (!movable[i])
CHECK_THAT((grid.vertices[i] - before.vertices[i]).norm(), WithinAbs(0.f, 1e-9f));
// Guard rails: each of these must leave the mesh byte-identical.
for (const auto &noop : { std::make_pair(0.f, 3), std::make_pair(0.5f, 0) }) {
indexed_triangle_set copy = before;
smooth_mesh_vertices(copy, movable, noop.first, noop.second);
CHECK(copy.vertices == before.vertices);
}
indexed_triangle_set copy = before;
smooth_mesh_vertices(copy, std::vector<uint8_t>(3, 1), 0.5f, 3); // mis-sized mask
CHECK(copy.vertices == before.vertices);
}
// Every undirected edge of a closed manifold mesh is shared by exactly two triangles. A T-junction
// (a hanging node where a refined region meets a coarse one) breaks that: the coarse side spans an
// edge that the fine side has replaced with two half-edges, so those three edges each show up an
// odd number of times. Counting edge uses is therefore an exact crack detector for a closed mesh.
static bool every_edge_used_twice(const indexed_triangle_set &its)
{
std::map<std::pair<int, int>, int> uses;
for (const auto &t : its.indices)
for (int e = 0; e < 3; ++e) {
int a = t[e], b = t[(e + 1) % 3];
if (a > b)
std::swap(a, b);
++uses[{ a, b }];
}
for (const auto &[edge, n] : uses)
if (n != 2)
return false;
return true;
}
TEST_CASE("TextureDisplacement: adaptive subdivision is conformal and region-restricted", "[TextureDisplacement]")
{
const indexed_triangle_set cube = its_make_cube(10., 10., 10.);
REQUIRE(every_edge_used_twice(cube)); // sanity: the input really is a closed manifold
auto longest_edge = [](const indexed_triangle_set &its, const stl_triangle_vertex_indices &t) {
float m = 0.f;
for (int e = 0; e < 3; ++e)
m = std::max(m, (its.vertices[t[e]] - its.vertices[t[(e + 1) % 3]]).norm());
return m;
};
SECTION("whole-mesh region refines everywhere and stays conformal")
{
std::vector<uint8_t> region(cube.indices.size(), 1);
std::vector<int> source;
const indexed_triangle_set out = subdivide_mesh_adaptive(cube, region, 3.f, 100000, &source);
CHECK(out.indices.size() > cube.indices.size()); // it actually refined
CHECK(every_edge_used_twice(out)); // ... without opening a single crack
// Refinement runs to completion, not for a fixed number of passes: with the whole mesh in the
// region and budget to spare, *every* edge really does end up at or below the target. This is
// the regression that matters - an earlier version quietly stopped a long way short, having
// spent its pass budget grading the coarse surroundings.
float worst = 0.f;
for (const auto &t : out.indices)
worst = std::max(worst, longest_edge(out, t));
CHECK(worst <= 3.f);
REQUIRE(source.size() == out.indices.size());
for (int s : source)
CHECK((s >= 0 && s < int(cube.indices.size()))); // every child names a real parent
}
SECTION("a partial region refines only there, and the boundary is still crack-free")
{
// Refine only the triangles whose centroid is in the upper (z > 5) half of the cube.
std::vector<uint8_t> region(cube.indices.size(), 0);
size_t region_count = 0;
for (size_t i = 0; i < cube.indices.size(); ++i) {
const auto &t = cube.indices[i];
const float cz = (cube.vertices[t[0]].z() + cube.vertices[t[1]].z() + cube.vertices[t[2]].z()) / 3.f;
if (cz > 5.f) {
region[i] = 1;
++region_count;
}
}
REQUIRE(region_count > 0);
std::vector<int> source;
const indexed_triangle_set out = subdivide_mesh_adaptive(cube, region, 2.f, 100000, &source);
CHECK(out.indices.size() > cube.indices.size());
CHECK(every_edge_used_twice(out)); // the refined/coarse seam has no T-junction
// Inside the region the target is actually met - refinement is not cut short by a pass budget.
// Outside it, only the graded transition band conformality requires is touched, so plenty of
// the unpainted mesh is still coarser than the target: the region was not a suggestion.
float max_in = 0.f, max_out = 0.f;
for (size_t i = 0; i < out.indices.size(); ++i) {
float &acc = region[source[i]] ? max_in : max_out;
acc = std::max(acc, longest_edge(out, out.indices[i]));
}
CHECK(max_in <= 2.f);
CHECK(max_out > 2.f);
std::vector<uint8_t> all(cube.indices.size(), 1);
const indexed_triangle_set whole = subdivide_mesh_adaptive(cube, all, 2.f, 100000);
CHECK(out.indices.size() < whole.indices.size()); // ... and it cost less than doing the lot
}
SECTION("the triangle budget caps the result and still leaves a conformal mesh")
{
std::vector<uint8_t> region(cube.indices.size(), 1);
const indexed_triangle_set out = subdivide_mesh_adaptive(cube, region, 0.05f, /*max_triangles*/ 500);
CHECK(out.indices.size() <= 500);
CHECK(out.indices.size() > cube.indices.size()); // it spent the budget rather than giving up
CHECK(every_edge_used_twice(out)); // stopping on the budget is not a crack
}
SECTION("an empty region is a no-op")
{
std::vector<uint8_t> region(cube.indices.size(), 0);
const indexed_triangle_set out = subdivide_mesh_adaptive(cube, region, 1.f, 100000, nullptr);
CHECK(out.indices.size() == cube.indices.size());
CHECK(out.vertices.size() == cube.vertices.size());
}
}
TEST_CASE("TextureDisplacement: feature-adaptive subdivision follows curvature, not slope", "[TextureDisplacement]")
{
// A flat sheet, tessellated into a regular grid to give the bisector something to work with.
indexed_triangle_set plane;
plane.vertices = { { 0.f, 0.f, 0.f }, { 1.f, 0.f, 0.f }, { 1.f, 1.f, 0.f }, { 0.f, 1.f, 0.f } };
plane.indices = { { 0, 1, 2 }, { 0, 2, 3 } };
const indexed_triangle_set grid = subdivide_mesh_uniform(plane, 0.15f, 5); // ~uniform grid of small triangles
REQUIRE(grid.indices.size() > 32);
const std::vector<uint8_t> region(grid.indices.size(), 1);
auto longest_edge = [](const indexed_triangle_set &its, const stl_triangle_vertex_indices &t) {
float m = 0.f;
for (int e = 0; e < 3; ++e)
m = std::max(m, (its.vertices[t[e]] - its.vertices[t[(e + 1) % 3]]).norm());
return m;
};
auto centroid_xy = [](const indexed_triangle_set &its, const stl_triangle_vertex_indices &t) {
return Vec2f((its.vertices[t[0]].x() + its.vertices[t[1]].x() + its.vertices[t[2]].x()) / 3.f,
(its.vertices[t[0]].y() + its.vertices[t[1]].y() + its.vertices[t[2]].y()) / 3.f);
};
SECTION("a sharp bump refines densely at its center and leaves flat corners coarse")
{
// A tight Gaussian bump at the sheet's center: strong curvature near (0.5, 0.5), flat far away.
HeightFieldSampler bump = [](const Vec3f &p, const Vec3f &) {
const float r2 = (p.x() - 0.5f) * (p.x() - 0.5f) + (p.y() - 0.5f) * (p.y() - 0.5f);
return 1.0f * std::exp(-r2 / 0.02f);
};
// Baseline max edge 0.3 is coarser than the grid's own edges, so the baseline adds nothing
// here - this isolates the *curvature* contribution (the grid already meets the baseline).
std::vector<int> source;
const indexed_triangle_set out =
subdivide_mesh_adaptive(grid, region, /*max edge*/ 0.3f, 200000, &source, bump, /*tol*/ 0.02f,
/*min_edge*/ 0.01f);
CHECK(out.indices.size() > grid.indices.size()); // the bump forced real refinement
// The largest triangle near the bump's center must be much smaller than the largest in a flat
// corner - i.e. triangles went where the curvature is, not spread evenly.
float near_max = 0.f, far_max = 0.f;
for (const auto &t : out.indices) {
const Vec2f c = centroid_xy(out, t);
const float r = (c - Vec2f(0.5f, 0.5f)).norm();
const float len = longest_edge(out, t);
if (r < 0.1f)
near_max = std::max(near_max, len);
else if (r > 0.45f)
far_max = std::max(far_max, len);
}
REQUIRE(near_max > 0.f);
REQUIRE(far_max > 0.f);
CHECK(near_max < far_max); // finer at the hill than on the flats
}
SECTION("a linear ramp has zero curvature and is left untouched")
{
// Height varies, but linearly - a flat triangle represents it exactly, so the chord error is
// zero everywhere and nothing should be split. This is the case a gradient-based criterion
// would wrongly over-refine.
HeightFieldSampler ramp = [](const Vec3f &p, const Vec3f &) { return 2.0f * p.x(); };
// Same coarse baseline (0.3) that the grid already meets, so any split would be curvature-
// driven - and a ramp has none.
const indexed_triangle_set out =
subdivide_mesh_adaptive(grid, region, /*max edge*/ 0.3f, 200000, nullptr, ramp, /*tol*/ 0.02f,
/*min_edge*/ 0.01f);
CHECK(out.indices.size() == grid.indices.size()); // not one extra triangle
}
SECTION("the max-edge baseline still applies in feature mode")
{
// A height field that is flat everywhere the four sample points of a coarse triangle happen to
// land, but not in between - the aliasing case where a chord test alone reports no error and
// refinement stalls before it ever starts. The baseline is what stops that: it guarantees a
// sampling density fine enough for the curvature test to see the texture at all.
HeightFieldSampler flat = [](const Vec3f &, const Vec3f &) { return 0.f; };
const indexed_triangle_set out =
subdivide_mesh_adaptive(grid, region, /*max edge*/ 0.03f, 200000, nullptr, flat, /*tol*/ 0.02f,
/*min_edge*/ 0.001f);
CHECK(out.indices.size() > grid.indices.size());
float worst = 0.f;
for (const auto &t : out.indices)
worst = std::max(worst, longest_edge(out, t));
CHECK(worst <= 0.03f);
}
}
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