3d Convex Hull

.gitmodules

@@ -14,3 +14,6 @@
 [submodule "src/third_party/clipper2"]
 	path = src/third_party/clipper2
 	url = https://github.com/AngusJohnson/clipper2
+[submodule "src/third_party/quickhull"]
+	path = src/third_party/quickhull
+	url = https://github.com/akuukka/quickhull

src/manifold/CMakeLists.txt

@@ -25,7 +25,7 @@ endif()
 target_include_directories(${PROJECT_NAME} PUBLIC ${PROJECT_SOURCE_DIR}/include)
 target_link_libraries(${PROJECT_NAME}
     PUBLIC utilities cross_section
-    PRIVATE collider polygon ${MANIFOLD_INCLUDE} graphlite Clipper2
+    PRIVATE collider polygon ${MANIFOLD_INCLUDE} graphlite Clipper2 quickhull
 )
 
 target_compile_features(${PROJECT_NAME}

src/manifold/include/manifold.h

@@ -234,6 +234,10 @@ class Manifold {
   Manifold TrimByPlane(glm::vec3 normal, float originOffset) const;
   ///@}
 
+  Manifold Hull() const;
+  static Manifold Hull(const std::vector<Manifold>& manifolds);
+  static Manifold Hull(const std::vector<glm::vec3>& pts);
+
   /** @name Testing hooks
    *  These are just for internal testing.
    */
@@ -249,7 +253,6 @@ class Manifold {
   Manifold(std::shared_ptr<CsgNode> pNode_);
   Manifold(std::shared_ptr<Impl> pImpl_);
   static Manifold Invalid();
-
   mutable std::shared_ptr<CsgNode> pNode_;
 
   CsgLeafNode& GetCsgLeafNode() const;

src/manifold/src/manifold.cpp

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <QuickHull.hpp>
 #include <algorithm>
 #include <map>
 #include <numeric>
@@ -775,4 +776,50 @@ Manifold Manifold::TrimByPlane(glm::vec3 normal, float originOffset) const {
 }
 
 ExecutionParams& ManifoldParams() { return params; }
-}  // namespace manifold
+
+/**
+ * Compute the convex hull of a set of points. If the given points are fewer
+ * than 4, or they are all coplanar, an empty Manifold will be returned.
+ *
+ * @param pts A vector of 3-dimensional points over which to compute a convex
+ * hull.
+ */
+Manifold Manifold::Hull(const std::vector<glm::vec3>& pts) {
+  const int numVert = pts.size();
+  if (numVert < 4) return Manifold();
+
+  std::vector<quickhull::Vector3<double>> vertices(numVert);
+  for (int i = 0; i < numVert; i++) {
+    vertices[i] = {pts[i].x, pts[i].y, pts[i].z};
+  }
+
+  quickhull::QuickHull<double> qh;
+  // bools: correct triangle winding, and use original indices
+  auto hull = qh.getConvexHull(vertices, false, true);
+  const auto& triangles = hull.getIndexBuffer();
+  const int numTris = triangles.size() / 3;
+
+  Mesh mesh;
+  mesh.vertPos = pts;
+  mesh.triVerts.reserve(numTris);
+  for (int i = 0; i < numTris; i++) {
+    const int j = i * 3;
+    mesh.triVerts.push_back({triangles[j], triangles[j + 1], triangles[j + 2]});
+  }
+  return Manifold(mesh);
+}
+
+/**
+ * Compute the convex hull of this manifold.
+ */
+Manifold Manifold::Hull() const { return Hull(GetMesh().vertPos); }
+
+/**
+ * Compute the convex hull enveloping a set of manifolds.
+ *
+ * @param manifolds A vector of manifolds over which to compute a convex hull.
+ */
+Manifold Manifold::Hull(const std::vector<Manifold>& manifolds) {
+  return Compose(manifolds).Hull();
+}
+}  // namespace manifold

src/third_party/CMakeLists.txt

@@ -6,5 +6,8 @@ set(CLIPPER2_EXAMPLES OFF)
 set(CLIPPER2_TESTS OFF)
 set(CLIPPER2_USINGZ "OFF" CACHE STRING "Preempt cache default of USINGZ (we only use 2d)")
 add_definitions(-D_HAS_EXCEPTIONS=0) # disable exceptions for STL
-
 add_subdirectory(clipper2/CPP)
+
+add_library(quickhull quickhull/QuickHull.cpp)
+target_include_directories(quickhull PUBLIC quickhull)
+target_compile_features(quickhull PUBLIC cxx_std_17)

test/manifold_test.cpp

@@ -711,4 +711,49 @@ TEST(Manifold, PinchedVert) {
   EXPECT_FALSE(touch.IsEmpty());
   EXPECT_EQ(touch.Status(), Manifold::Error::NoError);
   EXPECT_EQ(touch.Genus(), 0);
-}
+}
+
+TEST(Manifold, TictacHull) {
+  const float tictacRad = 100;
+  const float tictacHeight = 500;
+  const int tictacSeg = 1000;
+  const float tictacMid = tictacHeight - 2 * tictacRad;
+  const auto sphere = Manifold::Sphere(tictacRad, tictacSeg);
+  const std::vector<Manifold> spheres{sphere,
+                                      sphere.Translate({0, 0, tictacMid})};
+  const auto tictac = Manifold::Hull(spheres);
+
+#ifdef MANIFOLD_EXPORT
+  if (options.exportModels) {
+    ExportMesh("tictac_hull.glb", tictac.GetMesh(), {});
+  }
+#endif
+
+  EXPECT_EQ(sphere.NumVert() + tictacSeg, tictac.NumVert());
+}
+
+TEST(Manifold, HollowHull) {
+  auto sphere = Manifold::Sphere(100, 360);
+  auto hollow = sphere - sphere.Scale({0.8, 0.8, 0.8});
+  const float sphere_vol = sphere.GetProperties().volume;
+  EXPECT_FLOAT_EQ(hollow.Hull().GetProperties().volume, sphere_vol);
+}
+
+TEST(Manifold, CubeHull) {
+  std::vector<glm::vec3> cubePts = {
+      {0, 0, 0},       {1, 0, 0},   {0, 1, 0},      {0, 0, 1},  // corners
+      {1, 1, 0},       {0, 1, 1},   {1, 0, 1},      {1, 1, 1},  // corners
+      {0.5, 0.5, 0.5}, {0.5, 0, 0}, {0.5, 0.7, 0.2}  // internal points
+  };
+  auto cube = Manifold::Hull(cubePts);
+  EXPECT_FLOAT_EQ(cube.GetProperties().volume, 1);
+}
+
+TEST(Manifold, EmptyHull) {
+  const std::vector<glm::vec3> tooFew{{0, 0, 0}, {1, 0, 0}, {0, 1, 0}};
+  EXPECT_TRUE(Manifold::Hull(tooFew).IsEmpty());
+
+  const std::vector<glm::vec3> coplanar{
+      {0, 0, 0}, {1, 0, 0}, {0, 1, 0}, {1, 1, 0}};
+  EXPECT_TRUE(Manifold::Hull(coplanar).IsEmpty());
+}