Repair for printing (joins loose corners, drops empty and doubled faces and inside walls, turns faces out, closes holes): a button in Print and a command; joining points by a grid (an imported STL's 100k corners: milliseconds, not minutes); tests

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app.cpp

@@ -3334,6 +3334,12 @@ private:
         }
 
         ImGui::SeparatorText("Ready to print?");
+        if (!all.closed() || all.insideOut || all.tinyFaces) {
+            pushAccent();
+            if (ImGui::Button("Repair it (all at once)", ImVec2(w, 0))) repairSelected();
+            popAccent();
+            if (ImGui::IsItemHovered()) ImGui::SetTooltip("Joins loose corners, takes away empty and doubled faces, turns faces outwards, closes holes");
+        }
         if (all.openEdges) {
             bad(std::format("Not closed: {} edges have a face on one side only (holes). A slicer may fill them wrongly or not print it.", all.openEdges));
             if (ImGui::Button("Close the holes", ImVec2(w, 0))) {
@@ -7824,7 +7830,36 @@ private:
 
     // ── (being made) ──
     bool showPrintSize_ = false, liveMirror_ = false;
-    void repairSelected() {}
+    // Each picked object (or all, in the Print tab with none picked) made ready to print.
+    void repairSelected() {
+        std::vector<Object*> targets;
+        if (tab_ == Tab::Print) targets = printTargets();
+        else
+            for (Object& o : scene_.objects)
+                if (selected_.count(o.id)) targets.push_back(&o);
+        std::erase_if(targets, [](const Object* o) { return o->locked; });
+        if (targets.empty()) return say("Pick what to repair first");
+        if (mode_ == Mode::Edit) leaveEdit();
+        pushUndo();
+        fry::Repair all;
+        int still = 0;
+        for (Object* o : targets) {
+            const fry::Repair r = fry::repairForPrint(o->mesh);
+            all.joinedPoints += r.joinedPoints, all.emptyFaces += r.emptyFaces, all.doubledFaces += r.doubledFaces, all.turnedFaces += r.turnedFaces, all.closedHoles += r.closedHoles;
+            if (r.total()) handMade(*o), touched(o->id);
+            still += !checkForPrint(o->mesh).closed();
+        }
+        if (!all.total()) return takeBack(), say(still ? "Nothing it can repair by itself: look at what the Print tab says" : "Nothing to repair: ready to print");
+        std::vector<std::string> did;
+        if (all.joinedPoints) did.push_back(std::format("{} points joined", all.joinedPoints));
+        if (all.emptyFaces) did.push_back(std::format("{} empty faces gone", all.emptyFaces));
+        if (all.doubledFaces) did.push_back(std::format("{} doubled faces gone", all.doubledFaces));
+        if (all.turnedFaces) did.push_back(std::format("{} faces turned out", all.turnedFaces));
+        if (all.closedHoles) did.push_back(std::format("{} holes closed", all.closedHoles));
+        std::string text;
+        for (const std::string& d : did) text += (text.empty() ? "" : ", ") + d;
+        say("Repaired: " + text + (still ? std::format(". {} still not closed (see the Print tab)", still) : ". Ready to print"));
+    }
     void startSlide() {}
 
     std::string workspaceDir() const { return keel::prefPath() + "workspaces/"; }

src/mesh.cpp

@@ -4,6 +4,7 @@
 #include <cmath>
 #include <map>
 #include <numeric>
+#include <unordered_map>
 
 namespace fry {
 
@@ -376,13 +377,24 @@ bool makeFace(Mesh& m, const std::vector<int>& verts, const glm::vec3& towards)
 int mergeByDistance(Mesh& m, float distance) {
     std::vector<int> to(m.verts.size(), -1);
     std::vector<glm::vec3> kept;
+    // (kept points in a grid of cubes `distance` big: one is looked for in its own and the 26
+    // round it, not among all of them; an imported STL has hundreds of thousands)
+    const float cell = std::max(distance, 1e-9f);
+    auto cellOf = [&](const glm::vec3& p) { return glm::ivec3(glm::floor(p / cell)); };
+    auto key = [](glm::ivec3 c) { return (uint64_t(uint32_t(c.x) & 0x1FFFFF) << 42) | (uint64_t(uint32_t(c.y) & 0x1FFFFF) << 21) | uint64_t(uint32_t(c.z) & 0x1FFFFF); };
+    std::unordered_map<uint64_t, std::vector<int>> grid;
+    grid.reserve(m.verts.size());
     for (size_t v = 0; v < m.verts.size(); ++v) {
-        for (size_t k = 0; k < kept.size(); ++k)
-            if (glm::distance(kept[k], m.verts[v]) <= distance) {
-                to[v] = int(k);
-                break;
-            }
-        if (to[v] < 0) to[v] = int(kept.size()), kept.push_back(m.verts[v]);
+        const glm::ivec3 c = cellOf(m.verts[v]);
+        int best = -1;
+        for (int dx = -1; dx <= 1; ++dx)
+            for (int dy = -1; dy <= 1; ++dy)
+                for (int dz = -1; dz <= 1; ++dz)
+                    if (auto it = grid.find(key(c + glm::ivec3(dx, dy, dz))); it != grid.end())
+                        for (int k : it->second)
+                            if ((best < 0 || k < best) && glm::distance(kept[size_t(k)], m.verts[v]) <= distance) best = k; // (the first kept, as before)
+        if (best < 0) best = int(kept.size()), kept.push_back(m.verts[v]), grid[key(c)].push_back(best);
+        to[v] = best;
     }
     const int gone = int(m.verts.size() - kept.size());
     remapFaces(m, to);

src/mesh.h

@@ -178,6 +178,14 @@ bool overhangs(const Mesh& m, int face, float overhang, float bedZ);
 int closeHoles(Mesh& m);
 // Turns faces so each piece's all face the same way, outwards; how many were turned.
 int faceOutward(Mesh& m);
+// Made ready to print, as far as it can be without guessing: points in the same place joined (an
+// STL's corners come apart), faces with no area gone, faces there twice once (back to back: both
+// gone, an inside wall), faces turned the same way, holes closed. What it did.
+struct Repair {
+    int joinedPoints = 0, emptyFaces = 0, doubledFaces = 0, turnedFaces = 0, closedHoles = 0;
+    int total() const { return joinedPoints + emptyFaces + doubledFaces + turnedFaces + closedHoles; }
+};
+Repair repairForPrint(Mesh& m);
 
 // ── Its picture's layout ──
 

src/print.cpp

@@ -119,4 +119,60 @@ int faceOutward(Mesh& m) {
     return turned;
 }
 
+Repair repairForPrint(Mesh& m) {
+    Repair r;
+    if (m.verts.empty()) return r;
+    // (how near is "the same place": a millionth of its size, a micron at least)
+    const float size = glm::length(boundsMax(m) - boundsMin(m));
+    const size_t before = m.verts.size(), faces = m.faces.size();
+    mergeByDistance(m, std::max(size * 1e-6f, 1e-6f)); // (it drops faces left with fewer than three points: counted below)
+    r.joinedPoints = int(before - m.verts.size());
+    // Faces with a point twice in a row, fewer than three points, or no area.
+    const float tiny = std::max(size * size * 1e-12f, 1e-16f);
+    for (auto& f : m.faces) {
+        f.erase(std::unique(f.begin(), f.end()), f.end());
+        while (f.size() > 1 && f.front() == f.back()) f.pop_back();
+    }
+    std::erase_if(m.faces, [&](const std::vector<int>& f) { return f.size() < 3; });
+    for (size_t i = m.faces.size(); i-- > 0;)
+        if (faceArea(m, int(i)) <= tiny) m.faces.erase(m.faces.begin() + std::ptrdiff_t(i));
+    r.emptyFaces = int(faces - m.faces.size());
+    // The same face twice: once. Back to back (the same points, the other way round): neither.
+    std::map<std::vector<int>, std::vector<size_t>> same;
+    for (size_t i = 0; i < m.faces.size(); ++i) {
+        std::vector<int> key = m.faces[i];
+        std::sort(key.begin(), key.end());
+        same[key].push_back(i);
+    }
+    std::vector<char> drop(m.faces.size(), 0);
+    auto turn = [](const std::vector<int>& f) { // (the face started at its lowest point: two that turn the same way match)
+        std::vector<int> g = f;
+        std::rotate(g.begin(), std::min_element(g.begin(), g.end()), g.end());
+        return g;
+    };
+    for (const auto& [key, list] : same) {
+        if (list.size() < 2) continue;
+        int ways = 0, other = 0;
+        const std::vector<int> first = turn(m.faces[list[0]]);
+        for (size_t i : list) (turn(m.faces[i]) == first ? ways : other)++;
+        if (ways == other) // (back to back: an inside wall)
+            for (size_t i : list) drop[i] = 1;
+        else
+            for (size_t k = 1; k < list.size(); ++k) drop[list[k]] = 1;
+    }
+    size_t at = 0;
+    for (size_t i = 0; i < m.faces.size(); ++i)
+        if (!drop[i]) {
+            if (at != i) m.faces[at] = std::move(m.faces[i]); // (not onto itself: that empties it)
+            ++at;
+        }
+    r.doubledFaces = int(m.faces.size() - at);
+    m.faces.resize(at);
+    removeUnused(m);
+    r.turnedFaces = faceOutward(m);
+    r.closedHoles = closeHoles(m);
+    if (r.closedHoles) r.turnedFaces += faceOutward(m);
+    return r;
+}
+
 } // namespace fry

tests/mesh_test.cpp

@@ -14,6 +14,7 @@
 #include <glm/gtc/matrix_transform.hpp>
 
 #include <algorithm>
+#include <chrono>
 #include <filesystem>
 #include <memory>
 #include <fstream>
@@ -365,6 +366,46 @@ int main() {
         CHECK(combine(a, drill, Combine::Subtract) && checkForPrint(a).closed() && checkForPrint(a).volume < 1.0f && checkForPrint(a).volume > 0.85f,
               "a cylinder drilled through a cube: closed, %g m3", checkForPrint(a).volume);
     }
+    // Joining points is quick on a big mesh: a sphere in loose triangles, as an STL brings it.
+    {
+        const Mesh sphere = makeSphere(200, 100, 1.0f);
+        Mesh soup;
+        for (size_t f = 0; f < sphere.faces.size(); ++f)
+            for (const auto& t : triangulate(sphere, int(f))) {
+                soup.faces.push_back({int(soup.verts.size()), int(soup.verts.size()) + 1, int(soup.verts.size()) + 2});
+                for (int v : t) soup.verts.push_back(sphere.verts[size_t(v)]);
+            }
+        const size_t loose = soup.verts.size();
+        const auto t0 = std::chrono::steady_clock::now();
+        mergeByDistance(soup, 1e-6f);
+        const double ms = std::chrono::duration<double, std::milli>(std::chrono::steady_clock::now() - t0).count();
+        CHECK(soup.verts.size() == sphere.verts.size() && ms < 3000, "%zu loose points joined to %zu in %.0f ms", loose, soup.verts.size(), ms);
+    }
+    // Repair: a cube as an STL brings it (each face its own corners), one face missing, one
+    // turned in, one there twice, an inside wall: closed and the right way out after.
+    {
+        const Mesh good = makeCube(1.0f);
+        Mesh bad;
+        for (size_t f = 0; f < good.faces.size(); ++f) {
+            if (f == 2) continue; // (missing)
+            std::vector<int> face;
+            for (int v : good.faces[f]) face.push_back(int(bad.verts.size())), bad.verts.push_back(good.verts[size_t(v)] + glm::vec3(f == 4 ? 1e-8f : 0.0f));
+            if (f == 3) std::reverse(face.begin(), face.end()); // (turned in)
+            bad.faces.push_back(face);
+            if (f == 5) bad.faces.push_back(face); // (twice)
+        }
+        bad.faces.push_back({0, 1, 1}); // (no area)
+        const int a = int(bad.verts.size());
+        bad.verts.insert(bad.verts.end(), {{-0.5f, 0, -0.5f}, {0.5f, 0, -0.5f}, {0.5f, 0, 0.5f}, {-0.5f, 0, 0.5f}});
+        bad.faces.push_back({a, a + 1, a + 2, a + 3}), bad.faces.push_back({a + 3, a + 2, a + 1, a}); // (an inside wall, back to back)
+        CHECK(!checkForPrint(bad).closed(), "the broken cube is broken");
+        const Repair r = repairForPrint(bad);
+        const PrintCheck c = checkForPrint(bad);
+        CHECK(c.closed() && !c.insideOut && std::abs(c.volume - 1.0f) < 1e-4f && r.closedHoles == 1 && r.doubledFaces == 3 && r.emptyFaces == 1 && r.joinedPoints > 0,
+              "repair: closed, outwards, 1 m3 (joined %d, empty %d, doubled %d, turned %d, holes %d)", r.joinedPoints, r.emptyFaces, r.doubledFaces, r.turnedFaces, r.closedHoles);
+        Mesh fine = makeCube(1.0f);
+        CHECK(repairForPrint(fine).total() == 0 && fine.faces == good.faces, "a good cube: nothing to repair");
+    }
     // Spin: a square beside the axis turned all the way round is a ring (Pappus: its area times
     // how far its middle goes); a quarter turn has ends; a screw rises.
     {