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Rewrite adaptive subdivision to refine worst-first against a triangle budget

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This commit is contained in:
ExPikaPaka
2026-07-28 11:42:40 +02:00
parent 15fd3fc97c
commit 2a46197322
6 changed files with 877 additions and 246 deletions
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139
tests/libslic3r/test_texture_displacement.cpp
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@@ -1,6 +1,7 @@
#define NOMINMAX
#include <catch2/catch_all.hpp>
#include <cmath>
#include <fstream>
#include <boost/filesystem.hpp>
@@ -270,11 +271,20 @@ TEST_CASE("TextureDisplacement: adaptive subdivision is conformal and region-res
{
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, 12, &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
@@ -296,28 +306,133 @@ TEST_CASE("TextureDisplacement: adaptive subdivision is conformal and region-res
REQUIRE(region_count > 0);
std::vector<int> source;
const indexed_triangle_set out = subdivide_mesh_adaptive(cube, region, 2.f, 12, &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
// The region's own triangles came down in size; count how big the largest region-sourced
// output triangle is versus the largest region-sourced input triangle.
// 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 < cube.indices.size(); ++i)
if (region[i])
max_in = std::max(max_in, longest_edge(cube, cube.indices[i]));
for (size_t i = 0; i < out.indices.size(); ++i)
if (region[source[i]])
max_out = std::max(max_out, longest_edge(out, out.indices[i]));
CHECK(max_out < max_in); // refinement genuinely happened inside the region
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, 12, nullptr);
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);
}
}