Geometry Nodes: Add Convex Hull Node

This commit adds a node to output the convex hull of any input geometry
as a mesh, which is an enclosing geometry around a set of points.
All geometry types are supported, besides volumes.

The code supports operating on instances to avoid copying all input
geometry before the operation. The implementation uses the same backend
as the operation in edit mode, but uses Mesh directly instead of BMesh.

Attribute transfer is not supported currently, but would be a point of
improvement for the future if it can work in a predictable way on
different geometry input types.

Differential Revision: https://developer.blender.org/D10925

4 files changed, 341 insertions, 0 deletions

diff --git a/source/blender/nodes/CMakeLists.txt b/source/blender/nodes/CMakeLists.txt
index 7aaf28869de..025ce79ffc5 100644
--- a/source/blender/nodes/CMakeLists.txt
+++ b/source/blender/nodes/CMakeLists.txt
@@ -162,6 +162,7 @@ set(SRC
   geometry/nodes/node_geo_bounding_box.cc
   geometry/nodes/node_geo_collection_info.cc
   geometry/nodes/node_geo_common.cc
+  geometry/nodes/node_geo_convex_hull.cc
   geometry/nodes/node_geo_curve_length.cc  
   geometry/nodes/node_geo_curve_to_mesh.cc
   geometry/nodes/node_geo_curve_resample.cc
@@ -363,6 +364,23 @@ set(LIB
   bf_intern_sky
 )
 
+if(WITH_BULLET)
+  list(APPEND INC_SYS
+    ${BULLET_INCLUDE_DIRS}
+    "../../../intern/rigidbody/"
+  )
+  if(NOT WITH_SYSTEM_BULLET)
+  list(APPEND LIB
+    extern_bullet
+    )
+  endif()
+
+  list(APPEND LIB
+    ${BULLET_LIBRARIES}
+  )
+  add_definitions(-DWITH_BULLET)
+endif()
+
 if(WITH_PYTHON)
   list(APPEND INC
     ../python
diff --git a/source/blender/nodes/NOD_geometry.h b/source/blender/nodes/NOD_geometry.h
index df14fcfe5b4..b7e1b0b657c 100644
--- a/source/blender/nodes/NOD_geometry.h
+++ b/source/blender/nodes/NOD_geometry.h
@@ -50,6 +50,7 @@ void register_node_type_geo_attribute_remove(void);
 void register_node_type_geo_boolean(void);
 void register_node_type_geo_bounding_box(void);
 void register_node_type_geo_collection_info(void);
+void register_node_type_geo_convex_hull(void);
 void register_node_type_geo_curve_length(void);
 void register_node_type_geo_curve_to_mesh(void);
 void register_node_type_geo_curve_resample(void);
diff --git a/source/blender/nodes/NOD_static_types.h b/source/blender/nodes/NOD_static_types.h
index bfd99a2bb60..b255c6e5f23 100644
--- a/source/blender/nodes/NOD_static_types.h
+++ b/source/blender/nodes/NOD_static_types.h
@@ -289,6 +289,7 @@ DefNode(GeometryNode, GEO_NODE_ATTRIBUTE_VECTOR_ROTATE, def_geo_attribute_vector
 DefNode(GeometryNode, GEO_NODE_BOOLEAN, def_geo_boolean, "BOOLEAN", Boolean, "Boolean", "")
 DefNode(GeometryNode, GEO_NODE_BOUNDING_BOX, 0, "BOUNDING_BOX", BoundBox, "Bounding Box", "")
 DefNode(GeometryNode, GEO_NODE_COLLECTION_INFO, def_geo_collection_info, "COLLECTION_INFO", CollectionInfo, "Collection Info", "")
+DefNode(GeometryNode, GEO_NODE_CONVEX_HULL, 0, "CONVEX_HULL", ConvexHull, "Convex Hull", "")
 DefNode(GeometryNode, GEO_NODE_CURVE_LENGTH, 0, "CURVE_LENGTH", CurveLength, "Curve Length", "")
 DefNode(GeometryNode, GEO_NODE_CURVE_RESAMPLE, def_geo_curve_resample, "CURVE_RESAMPLE", CurveResample, "Resample Curve", "")
 DefNode(GeometryNode, GEO_NODE_CURVE_TO_MESH, 0, "CURVE_TO_MESH", CurveToMesh, "Curve to Mesh", "")
diff --git a/source/blender/nodes/geometry/nodes/node_geo_convex_hull.cc b/source/blender/nodes/geometry/nodes/node_geo_convex_hull.cc
new file mode 100644
index 00000000000..b1b17a321b8
--- /dev/null
+++ b/source/blender/nodes/geometry/nodes/node_geo_convex_hull.cc
@@ -0,0 +1,321 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include "DNA_mesh_types.h"
+#include "DNA_meshdata_types.h"
+#include "DNA_pointcloud_types.h"
+
+#include "BKE_material.h"
+#include "BKE_mesh.h"
+#include "BKE_spline.hh"
+
+#include "node_geometry_util.hh"
+
+#ifdef WITH_BULLET
+#  include "RBI_hull_api.h"
+#endif
+
+static bNodeSocketTemplate geo_node_convex_hull_in[] = {
+    {SOCK_GEOMETRY, N_("Geometry")},
+    {-1, ""},
+};
+
+static bNodeSocketTemplate geo_node_convex_hull_out[] = {
+    {SOCK_GEOMETRY, N_("Convex Hull")},
+    {-1, ""},
+};
+
+namespace blender::nodes {
+
+using bke::GeometryInstanceGroup;
+
+#ifdef WITH_BULLET
+
+static Mesh *hull_from_bullet(const Mesh *mesh, Span<float3> coords)
+{
+  plConvexHull hull = plConvexHullCompute((float(*)[3])coords.data(), coords.size());
+
+  const int num_verts = plConvexHullNumVertices(hull);
+  const int num_faces = num_verts <= 2 ? 0 : plConvexHullNumFaces(hull);
+  const int num_loops = num_verts <= 2 ? 0 : plConvexHullNumLoops(hull);
+  /* Half as many edges as loops, because the mesh is manifold. */
+  const int num_edges = num_verts == 2 ? 1 : num_verts < 2 ? 0 : num_loops / 2;
+
+  /* Create Mesh *result with proper capacity. */
+  Mesh *result;
+  if (mesh) {
+    result = BKE_mesh_new_nomain_from_template(
+        mesh, num_verts, num_edges, 0, num_loops, num_faces);
+  }
+  else {
+    result = BKE_mesh_new_nomain(num_verts, num_edges, 0, num_loops, num_faces);
+    BKE_id_material_eval_ensure_default_slot(&result->id);
+  }
+
+  /* Copy vertices. */
+  for (const int i : IndexRange(num_verts)) {
+    float co[3];
+    int original_index;
+    plConvexHullGetVertex(hull, i, co, &original_index);
+
+    if (original_index >= 0 && original_index < coords.size()) {
+#  if 0 /* Disabled because it only works for meshes, not predictable enough. */
+      /* Copy custom data on vertices, like vertex groups etc. */
+      if (mesh && original_index < mesh->totvert) {
+        CustomData_copy_data(&mesh->vdata, &result->vdata, (int)original_index, (int)i, 1);
+      }
+#  endif
+      /* Copy the position of the original point. */
+      copy_v3_v3(result->mvert[i].co, co);
+    }
+    else {
+      BLI_assert(!"Unexpected new vertex in hull output");
+    }
+  }
+
+  /* Copy edges and loops. */
+
+  /* NOTE: ConvexHull from Bullet uses a half-edge data structure
+   * for its mesh. To convert that, each half-edge needs to be converted
+   * to a loop and edges need to be created from that. */
+  Array<MLoop> mloop_src(num_loops);
+  uint edge_index = 0;
+  for (const int i : IndexRange(num_loops)) {
+    int v_from;
+    int v_to;
+    plConvexHullGetLoop(hull, i, &v_from, &v_to);
+
+    mloop_src[i].v = (uint)v_from;
+    /* Add edges for ascending order loops only. */
+    if (v_from < v_to) {
+      MEdge &edge = result->medge[edge_index];
+      edge.v1 = v_from;
+      edge.v2 = v_to;
+      edge.flag = ME_EDGEDRAW | ME_EDGERENDER;
+
+      /* Write edge index into both loops that have it. */
+      int reverse_index = plConvexHullGetReversedLoopIndex(hull, i);
+      mloop_src[i].e = edge_index;
+      mloop_src[reverse_index].e = edge_index;
+      edge_index++;
+    }
+  }
+  if (num_edges == 1) {
+    /* In this case there are no loops. */
+    MEdge &edge = result->medge[0];
+    edge.v1 = 0;
+    edge.v2 = 1;
+    edge.flag |= ME_EDGEDRAW | ME_EDGERENDER | ME_LOOSEEDGE;
+    edge_index++;
+  }
+  BLI_assert(edge_index == num_edges);
+
+  /* Copy faces. */
+  Array<int> loops;
+  int j = 0;
+  MLoop *loop = result->mloop;
+  for (const int i : IndexRange(num_faces)) {
+    const int len = plConvexHullGetFaceSize(hull, i);
+
+    BLI_assert(len > 2);
+
+    /* Get face loop indices. */
+    loops.reinitialize(len);
+    plConvexHullGetFaceLoops(hull, i, loops.data());
+
+    MPoly &face = result->mpoly[i];
+    face.loopstart = j;
+    face.totloop = len;
+    for (const int k : IndexRange(len)) {
+      MLoop &src_loop = mloop_src[loops[k]];
+      loop->v = src_loop.v;
+      loop->e = src_loop.e;
+      loop++;
+    }
+    j += len;
+  }
+
+  plConvexHullDelete(hull);
+
+  BKE_mesh_calc_normals(result);
+  return result;
+}
+
+static Mesh *compute_hull(const GeometrySet &geometry_set)
+{
+  int span_count = 0;
+  int count = 0;
+  int total_size = 0;
+
+  Span<float3> positions_span;
+
+  if (geometry_set.has_mesh()) {
+    count++;
+    const MeshComponent *component = geometry_set.get_component_for_read<MeshComponent>();
+    total_size += component->attribute_domain_size(ATTR_DOMAIN_POINT);
+  }
+
+  if (geometry_set.has_pointcloud()) {
+    count++;
+    span_count++;
+    const PointCloudComponent *component =
+        geometry_set.get_component_for_read<PointCloudComponent>();
+    GVArray_Typed<float3> varray = component->attribute_get_for_read<float3>(
+        "position", ATTR_DOMAIN_POINT, {0, 0, 0});
+    total_size += varray->size();
+    positions_span = varray->get_internal_span();
+  }
+
+  if (geometry_set.has_curve()) {
+    const CurveEval &curve = *geometry_set.get_curve_for_read();
+    for (const SplinePtr &spline : curve.splines()) {
+      positions_span = spline->evaluated_positions();
+      total_size += positions_span.size();
+      count++;
+      span_count++;
+    }
+  }
+
+  if (count == 0) {
+    return nullptr;
+  }
+
+  /* If there is only one positions virtual array and it is already contiguous, avoid copying
+   * all of the positions and instead pass the span directly to the convex hull function. */
+  if (span_count == 1 && count == 1) {
+    return hull_from_bullet(nullptr, positions_span);
+  }
+
+  Array<float3> positions(total_size);
+  int offset = 0;
+
+  if (geometry_set.has_mesh()) {
+    const MeshComponent *component = geometry_set.get_component_for_read<MeshComponent>();
+    GVArray_Typed<float3> varray = component->attribute_get_for_read<float3>(
+        "position", ATTR_DOMAIN_POINT, {0, 0, 0});
+    varray->materialize(positions.as_mutable_span().slice(offset, varray.size()));
+    offset += varray.size();
+  }
+
+  if (geometry_set.has_pointcloud()) {
+    const PointCloudComponent *component =
+        geometry_set.get_component_for_read<PointCloudComponent>();
+    GVArray_Typed<float3> varray = component->attribute_get_for_read<float3>(
+        "position", ATTR_DOMAIN_POINT, {0, 0, 0});
+    varray->materialize(positions.as_mutable_span().slice(offset, varray.size()));
+    offset += varray.size();
+  }
+
+  if (geometry_set.has_curve()) {
+    const CurveEval &curve = *geometry_set.get_curve_for_read();
+    for (const SplinePtr &spline : curve.splines()) {
+      Span<float3> array = spline->evaluated_positions();
+      positions.as_mutable_span().slice(offset, array.size()).copy_from(array);
+      offset += array.size();
+    }
+  }
+
+  return hull_from_bullet(geometry_set.get_mesh_for_read(), positions);
+}
+
+static void read_positions(const GeometryComponent &component,
+                           Span<float4x4> transforms,
+                           Vector<float3> *r_coords)
+{
+  GVArray_Typed<float3> positions = component.attribute_get_for_read<float3>(
+      "position", ATTR_DOMAIN_POINT, {0, 0, 0});
+
+  /* NOTE: could use convex hull operation here to
+   * cut out some vertices, before accumulating,
+   * but can also be done by the user beforehand. */
+
+  r_coords->reserve(r_coords->size() + positions.size() * transforms.size());
+  for (const float4x4 &transform : transforms) {
+    for (const int i : positions.index_range()) {
+      const float3 position = positions[i];
+      const float3 transformed_position = transform * position;
+      r_coords->append(transformed_position);
+    }
+  }
+}
+
+static void read_curve_positions(const CurveEval &curve,
+                                 Span<float4x4> transforms,
+                                 Vector<float3> *r_coords)
+{
+  const Array<int> offsets = curve.evaluated_point_offsets();
+  const int total_size = offsets.last();
+  r_coords->reserve(r_coords->size() + total_size * transforms.size());
+  for (const SplinePtr &spline : curve.splines()) {
+    Span<float3> positions = spline->evaluated_positions();
+    for (const float4x4 &transform : transforms) {
+      for (const float3 &position : positions) {
+        r_coords->append(transform * position);
+      }
+    }
+  }
+}
+
+#endif /* WITH_BULLET */
+
+static void geo_node_convex_hull_exec(GeoNodeExecParams params)
+{
+  GeometrySet geometry_set = params.extract_input<GeometrySet>("Geometry");
+
+#ifdef WITH_BULLET
+  Mesh *mesh = nullptr;
+  if (geometry_set.has_instances()) {
+    Vector<GeometryInstanceGroup> set_groups;
+    bke::geometry_set_gather_instances(geometry_set, set_groups);
+
+    Vector<float3> coords;
+
+    for (const GeometryInstanceGroup &set_group : set_groups) {
+      const GeometrySet &set = set_group.geometry_set;
+      Span<float4x4> transforms = set_group.transforms;
+
+      if (set.has_pointcloud()) {
+        read_positions(*set.get_component_for_read<PointCloudComponent>(), transforms, &coords);
+      }
+      if (set.has_mesh()) {
+        read_positions(*set.get_component_for_read<MeshComponent>(), transforms, &coords);
+      }
+      if (set.has_curve()) {
+        read_curve_positions(*set.get_curve_for_read(), transforms, &coords);
+      }
+    }
+    mesh = hull_from_bullet(nullptr, coords);
+  }
+  else {
+    mesh = compute_hull(geometry_set);
+  }
+  params.set_output("Convex Hull", GeometrySet::create_with_mesh(mesh));
+#else
+  params.set_output("Convex Hull", geometry_set);
+#endif /* WITH_BULLET */
+}
+
+}  // namespace blender::nodes
+
+void register_node_type_geo_convex_hull()
+{
+  static bNodeType ntype;
+
+  geo_node_type_base(&ntype, GEO_NODE_CONVEX_HULL, "Convex Hull", NODE_CLASS_GEOMETRY, 0);
+  node_type_socket_templates(&ntype, geo_node_convex_hull_in, geo_node_convex_hull_out);
+  ntype.geometry_node_execute = blender::nodes::geo_node_convex_hull_exec;
+  nodeRegisterType(&ntype);
+}