Volumes: new Volume to Mesh modifier

This modifier is the opposite of the recently added Mesh to Volume modifier.
It converts the "surface" of a volume into a mesh. The "surface" is defined
by a threshold value. All voxels with a density higher than the threshold
are considered to be inside the volume, while all others will be outside.

By default, the resolution of the generated mesh depends on the voxel
size of the volume grid. The resolution can be customized. It should be
noted that a lower resolution might not make this modifier faster. This
is because we have to downsample the openvdb grid, which isn't a cheap
operation.

Converting a mesh to a volume and then back to a mesh is possible,
but it does require two separate mesh objects for now.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D9141

1 files changed, 343 insertions, 0 deletions

diff --git a/source/blender/modifiers/intern/MOD_volume_to_mesh.cc b/source/blender/modifiers/intern/MOD_volume_to_mesh.cc
new file mode 100644
index 00000000000..ea292155d3c
--- /dev/null
+++ b/source/blender/modifiers/intern/MOD_volume_to_mesh.cc
@@ -0,0 +1,343 @@
+/*
+ * 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.
+ */
+
+/** \file
+ * \ingroup modifiers
+ */
+
+#include <vector>
+
+#include "BKE_lib_query.h"
+#include "BKE_mesh.h"
+#include "BKE_modifier.h"
+#include "BKE_volume.h"
+
+#include "MOD_modifiertypes.h"
+#include "MOD_ui_common.h"
+
+#include "DNA_mesh_types.h"
+#include "DNA_meshdata_types.h"
+#include "DNA_modifier_types.h"
+#include "DNA_object_types.h"
+#include "DNA_screen_types.h"
+#include "DNA_volume_types.h"
+
+#include "UI_interface.h"
+#include "UI_resources.h"
+
+#include "RNA_access.h"
+
+#include "BLI_float4x4.hh"
+#include "BLI_math_vector.h"
+#include "BLI_span.hh"
+#include "BLI_timeit.hh"
+
+#ifdef WITH_OPENVDB
+#  include <openvdb/tools/GridTransformer.h>
+#  include <openvdb/tools/VolumeToMesh.h>
+#endif
+
+using blender::float3;
+using blender::float4x4;
+using blender::Span;
+
+static void initData(ModifierData *md)
+{
+  VolumeToMeshModifierData *vmmd = reinterpret_cast<VolumeToMeshModifierData *>(md);
+  vmmd->object = NULL;
+  vmmd->threshold = 0.1f;
+  strncpy(vmmd->grid_name, "density", MAX_NAME);
+  vmmd->adaptivity = 0.0f;
+  vmmd->resolution_mode = VOLUME_TO_MESH_RESOLUTION_MODE_GRID;
+  vmmd->voxel_amount = 32;
+  vmmd->voxel_size = 0.1f;
+  vmmd->flag = 0;
+}
+
+static void updateDepsgraph(ModifierData *md, const ModifierUpdateDepsgraphContext *ctx)
+{
+  VolumeToMeshModifierData *vmmd = reinterpret_cast<VolumeToMeshModifierData *>(md);
+  DEG_add_modifier_to_transform_relation(ctx->node, "Volume to Mesh Modifier");
+  if (vmmd->object) {
+    DEG_add_object_relation(
+        ctx->node, vmmd->object, DEG_OB_COMP_GEOMETRY, "Volume to Mesh Modifier");
+    DEG_add_object_relation(
+        ctx->node, vmmd->object, DEG_OB_COMP_TRANSFORM, "Volume to Mesh Modifier");
+  }
+}
+
+static void foreachIDLink(ModifierData *md, Object *ob, IDWalkFunc walk, void *userData)
+{
+  VolumeToMeshModifierData *vmmd = reinterpret_cast<VolumeToMeshModifierData *>(md);
+  walk(userData, ob, (ID **)&vmmd->object, IDWALK_CB_NOP);
+}
+
+static void panel_draw(const bContext *UNUSED(C), Panel *panel)
+{
+  uiLayout *layout = panel->layout;
+
+  PointerRNA *ptr = modifier_panel_get_property_pointers(panel, NULL);
+  VolumeToMeshModifierData *vmmd = static_cast<VolumeToMeshModifierData *>(ptr->data);
+
+  uiLayoutSetPropSep(layout, true);
+  uiLayoutSetPropDecorate(layout, false);
+
+  {
+    uiLayout *col = uiLayoutColumn(layout, false);
+    uiItemR(col, ptr, "object", 0, NULL, ICON_NONE);
+    uiItemR(col, ptr, "grid_name", 0, NULL, ICON_NONE);
+  }
+
+  {
+    uiLayout *col = uiLayoutColumn(layout, false);
+    uiItemR(col, ptr, "resolution_mode", 0, NULL, ICON_NONE);
+    if (vmmd->resolution_mode == VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_AMOUNT) {
+      uiItemR(col, ptr, "voxel_amount", 0, NULL, ICON_NONE);
+    }
+    else if (vmmd->resolution_mode == VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_SIZE) {
+      uiItemR(col, ptr, "voxel_size", 0, NULL, ICON_NONE);
+    }
+  }
+
+  {
+    uiLayout *col = uiLayoutColumn(layout, false);
+    uiItemR(col, ptr, "threshold", 0, NULL, ICON_NONE);
+    uiItemR(col, ptr, "adaptivity", 0, NULL, ICON_NONE);
+    uiItemR(col, ptr, "use_smooth_shade", 0, NULL, ICON_NONE);
+  }
+
+  modifier_panel_end(layout, ptr);
+}
+
+static void panelRegister(ARegionType *region_type)
+{
+  modifier_panel_register(region_type, eModifierType_VolumeToMesh, panel_draw);
+}
+
+#ifdef WITH_OPENVDB
+
+struct VolumeToMeshOp {
+  const openvdb::GridBase &base_grid;
+  VolumeToMeshModifierData &vmmd;
+  const ModifierEvalContext &ctx;
+  std::vector<openvdb::Vec3s> verts;
+  std::vector<openvdb::Vec3I> tris;
+  std::vector<openvdb::Vec4I> quads;
+
+  template<typename GridType> bool operator()()
+  {
+    if constexpr (std::is_scalar_v<typename GridType::ValueType>) {
+      this->generate_mesh_data<GridType>();
+      return true;
+    }
+    else {
+      return false;
+    }
+  }
+
+  template<typename GridType> void generate_mesh_data()
+  {
+    /* Make a new transform from the index space into the mesh object space. */
+    openvdb::math::Transform::Ptr transform = this->base_grid.transform().copy();
+    transform->postMult(openvdb::Mat4d((float *)vmmd.object->obmat));
+    openvdb::Mat4d imat = openvdb::Mat4d((float *)ctx.object->imat);
+    /* `imat` had floating point issues and wasn't affine. */
+    imat.setCol(3, openvdb::Vec4d(0, 0, 0, 1));
+    transform->postMult(imat);
+
+    /* Create a new grid with a different transform. The underlying tree is shared. */
+    typename GridType::ConstPtr grid = openvdb::gridConstPtrCast<GridType>(
+        this->base_grid.copyGridReplacingTransform(transform));
+
+    if (this->vmmd.resolution_mode == VOLUME_TO_MESH_RESOLUTION_MODE_GRID) {
+      this->grid_to_mesh(*grid);
+      return;
+    }
+
+    const float resolution_factor = this->compute_resolution_factor(*grid);
+    typename GridType::Ptr temp_grid = this->create_grid_with_changed_resolution(
+        *grid, resolution_factor);
+    this->grid_to_mesh(*temp_grid);
+  }
+
+  template<typename GridType>
+  typename GridType::Ptr create_grid_with_changed_resolution(const GridType &old_grid,
+                                                             const float resolution_factor)
+  {
+    BLI_assert(resolution_factor > 0.0f);
+
+    openvdb::Mat4R xform;
+    xform.setToScale(openvdb::Vec3d(resolution_factor));
+    openvdb::tools::GridTransformer transformer{xform};
+
+    typename GridType::Ptr new_grid = GridType::create();
+    transformer.transformGrid<openvdb::tools::BoxSampler>(old_grid, *new_grid);
+    new_grid->transform() = old_grid.transform();
+    new_grid->transform().preScale(1.0f / resolution_factor);
+    return new_grid;
+  }
+
+  float compute_resolution_factor(const openvdb::GridBase &grid) const
+  {
+    const openvdb::Vec3s voxel_size{grid.voxelSize()};
+    const float current_voxel_size = std::max({voxel_size[0], voxel_size[1], voxel_size[2]});
+    const float desired_voxel_size = this->compute_desired_voxel_size(grid);
+    return current_voxel_size / desired_voxel_size;
+  }
+
+  float compute_desired_voxel_size(const openvdb::GridBase &grid) const
+  {
+    if (this->vmmd.resolution_mode == VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_SIZE) {
+      return this->vmmd.voxel_size;
+    }
+    const openvdb::CoordBBox coord_bbox = base_grid.evalActiveVoxelBoundingBox();
+    const openvdb::BBoxd bbox = grid.transform().indexToWorld(coord_bbox);
+    const float max_extent = bbox.extents()[bbox.maxExtent()];
+    const float voxel_size = max_extent / this->vmmd.voxel_amount;
+    return voxel_size;
+  }
+
+  template<typename GridType> void grid_to_mesh(const GridType &grid)
+  {
+    openvdb::tools::volumeToMesh(
+        grid, this->verts, this->tris, this->quads, this->vmmd.threshold, this->vmmd.adaptivity);
+  }
+};
+
+static Mesh *new_mesh_from_openvdb_data(Span<openvdb::Vec3s> verts,
+                                        Span<openvdb::Vec3I> tris,
+                                        Span<openvdb::Vec4I> quads)
+{
+  const int tot_loops = 3 * tris.size() + 4 * quads.size();
+  const int tot_polys = tris.size() + quads.size();
+
+  Mesh *mesh = BKE_mesh_new_nomain(verts.size(), 0, 0, tot_loops, tot_polys);
+
+  /* Write vertices. */
+  for (const int i : verts.index_range()) {
+    const blender::float3 co = blender::float3(verts[i].asV());
+    copy_v3_v3(mesh->mvert[i].co, co);
+  }
+
+  /* Write triangles. */
+  for (const int i : tris.index_range()) {
+    mesh->mpoly[i].loopstart = 3 * i;
+    mesh->mpoly[i].totloop = 3;
+    for (int j = 0; j < 3; j++) {
+      mesh->mloop[3 * i + j].v = tris[i][j];
+    }
+  }
+
+  /* Write quads. */
+  const int poly_offset = tris.size();
+  const int loop_offset = tris.size() * 3;
+  for (const int i : quads.index_range()) {
+    mesh->mpoly[poly_offset + i].loopstart = loop_offset + 4 * i;
+    mesh->mpoly[poly_offset + i].totloop = 4;
+    for (int j = 0; j < 4; j++) {
+      mesh->mloop[loop_offset + 4 * i + j].v = quads[i][j];
+    }
+  }
+
+  BKE_mesh_calc_edges(mesh, false, false);
+  BKE_mesh_calc_normals(mesh);
+  return mesh;
+}
+#endif
+
+static Mesh *modifyMesh(ModifierData *md, const ModifierEvalContext *ctx, Mesh *input_mesh)
+{
+#ifdef WITH_OPENVDB
+  VolumeToMeshModifierData *vmmd = reinterpret_cast<VolumeToMeshModifierData *>(md);
+  if (vmmd->object == nullptr) {
+    return input_mesh;
+  }
+  if (vmmd->object->type != OB_VOLUME) {
+    return input_mesh;
+  }
+  if (vmmd->resolution_mode == VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_SIZE &&
+      vmmd->voxel_size == 0.0f) {
+    return input_mesh;
+  }
+  if (vmmd->resolution_mode == VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_AMOUNT &&
+      vmmd->voxel_amount == 0) {
+    return input_mesh;
+  }
+
+  Volume *volume = static_cast<Volume *>(vmmd->object->data);
+
+  VolumeGrid *volume_grid = BKE_volume_grid_find(volume, vmmd->grid_name);
+  if (volume_grid == nullptr) {
+    BKE_modifier_set_error(md, "Cannot find '%s' grid", vmmd->grid_name);
+    return input_mesh;
+  }
+
+  const openvdb::GridBase::ConstPtr grid = BKE_volume_grid_openvdb_for_read(volume, volume_grid);
+
+  const VolumeGridType grid_type = BKE_volume_grid_type(volume_grid);
+  VolumeToMeshOp to_mesh_op{*grid, *vmmd, *ctx};
+  if (!BKE_volume_grid_type_operation(grid_type, to_mesh_op)) {
+    BKE_modifier_set_error(md, "Expected a scalar grid");
+    return input_mesh;
+  }
+
+  Mesh *mesh = new_mesh_from_openvdb_data(to_mesh_op.verts, to_mesh_op.tris, to_mesh_op.quads);
+  BKE_mesh_copy_settings(mesh, input_mesh);
+  if (vmmd->flag & VOLUME_TO_MESH_USE_SMOOTH_SHADE) {
+    BKE_mesh_smooth_flag_set(mesh, true);
+  }
+  return mesh;
+#else
+  UNUSED_VARS(md, ctx);
+  BKE_modifier_set_error(md, "Compiled without OpenVDB");
+  return input_mesh;
+#endif
+}
+
+ModifierTypeInfo modifierType_VolumeToMesh = {
+    /* name */ "Volume to Mesh",
+    /* structName */ "VolumeToMeshModifierData",
+    /* structSize */ sizeof(VolumeToMeshModifierData),
+    /* srna */ &RNA_VolumeToMeshModifier,
+    /* type */ eModifierTypeType_Constructive,
+    /* flags */ eModifierTypeFlag_AcceptsMesh,
+    /* icon */ ICON_VOLUME_DATA, /* TODO: Use correct icon. */
+
+    /* copyData */ BKE_modifier_copydata_generic,
+
+    /* deformVerts */ NULL,
+    /* deformMatrices */ NULL,
+    /* deformVertsEM */ NULL,
+    /* deformMatricesEM */ NULL,
+    /* modifyMesh */ modifyMesh,
+    /* modifyHair */ NULL,
+    /* modifyPointCloud */ NULL,
+    /* modifyVolume */ NULL,
+
+    /* initData */ initData,
+    /* requiredDataMask */ NULL,
+    /* freeData */ NULL,
+    /* isDisabled */ NULL,
+    /* updateDepsgraph */ updateDepsgraph,
+    /* dependsOnTime */ NULL,
+    /* dependsOnNormals */ NULL,
+    /* foreachIDLink */ foreachIDLink,
+    /* foreachTexLink */ NULL,
+    /* freeRuntimeData */ NULL,
+    /* panelRegister */ panelRegister,
+    /* blendWrite */ NULL,
+    /* blendRead */ NULL,
+};