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, 89 insertions, 0 deletions

diff --git a/source/blender/makesrna/intern/rna_modifier.c b/source/blender/makesrna/intern/rna_modifier.c
index 0010e473924..48ea894aba1 100644
--- a/source/blender/makesrna/intern/rna_modifier.c
+++ b/source/blender/makesrna/intern/rna_modifier.c
@@ -198,6 +198,11 @@ const EnumPropertyItem rna_enum_object_modifier_type_items[] = {
      ICON_VOLUME_DATA,
      "Mesh to Volume",
      ""}, /* TODO: Use correct icon. */
+    {eModifierType_VolumeToMesh,
+     "VOLUME_TO_MESH",
+     ICON_VOLUME_DATA,
+     "Volume to Mesh",
+     ""}, /* TODO: Use correct icon. */
     {0, "", 0, N_("Deform"), ""},
     {eModifierType_Armature,
      "ARMATURE",
@@ -7133,6 +7138,89 @@ static void rna_def_modifier_volume_displace(BlenderRNA *brna)
   RNA_define_lib_overridable(false);
 }
 
+static void rna_def_modifier_volume_to_mesh(BlenderRNA *brna)
+{
+  StructRNA *srna;
+  PropertyRNA *prop;
+
+  static EnumPropertyItem resolution_mode_items[] = {
+      {VOLUME_TO_MESH_RESOLUTION_MODE_GRID,
+       "GRID",
+       0,
+       "Grid",
+       "Use resolution of the volume grid"},
+      {VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_AMOUNT,
+       "VOXEL_AMOUNT",
+       0,
+       "Voxel Amount",
+       "Desired number of voxels along one axis"},
+      {VOLUME_TO_MESH_RESOLUTION_MODE_VOXEL_SIZE,
+       "VOXEL_SIZE",
+       0,
+       "Voxel Size",
+       "Desired voxel side length"},
+      {0, NULL, 0, NULL, NULL},
+  };
+
+  srna = RNA_def_struct(brna, "VolumeToMeshModifier", "Modifier");
+  RNA_def_struct_ui_text(srna, "Volume to Mesh Modifier", "");
+  RNA_def_struct_sdna(srna, "VolumeToMeshModifierData");
+  RNA_def_struct_ui_icon(srna, ICON_VOLUME_DATA); /* TODO: Use correct icon. */
+
+  RNA_define_lib_overridable(true);
+
+  prop = RNA_def_property(srna, "object", PROP_POINTER, PROP_NONE);
+  RNA_def_property_ui_text(prop, "Object", "Object");
+  RNA_def_property_flag(prop, PROP_EDITABLE | PROP_ID_SELF_CHECK);
+  RNA_def_property_update(prop, 0, "rna_Modifier_dependency_update");
+
+  prop = RNA_def_property(srna, "threshold", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_ui_text(
+      prop, "Threshold", "Voxels with a larger value are inside the generated mesh");
+  RNA_def_property_range(prop, 0.0f, FLT_MAX);
+  RNA_def_property_ui_range(prop, 0.001f, 1.0f, 0.1f, 5);
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "adaptivity", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_ui_text(
+      prop,
+      "Adaptivity",
+      "Reduces the final face count by simplifying geometry where detail is not needed");
+  RNA_def_property_range(prop, 0.0f, 1.0f);
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "use_smooth_shade", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", VOLUME_TO_MESH_USE_SMOOTH_SHADE);
+  RNA_def_property_ui_text(
+      prop, "Smooth Shading", "Output faces with smooth shading rather than flat shaded");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "grid_name", PROP_STRING, PROP_NONE);
+  RNA_def_property_ui_text(
+      prop, "Grid Name", "Grid in the volume object that is converted to a mesh");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "resolution_mode", PROP_ENUM, PROP_NONE);
+  RNA_def_property_enum_items(prop, resolution_mode_items);
+  RNA_def_property_ui_text(
+      prop, "Resolution Mode", "Mode for how the desired voxel size is specified");
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "voxel_size", PROP_FLOAT, PROP_NONE);
+  RNA_def_property_ui_text(
+      prop, "Voxel Size", "Smaller values result in a higher resolution output");
+  RNA_def_property_range(prop, 0.0, FLT_MAX);
+  RNA_def_property_ui_range(prop, 0.0, FLT_MAX, 0.01, 4);
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  prop = RNA_def_property(srna, "voxel_amount", PROP_INT, PROP_NONE);
+  RNA_def_property_ui_text(prop, "Voxel Amount", "Approximate number of voxels along one axis");
+  RNA_def_property_range(prop, 0, INT_MAX);
+  RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+  RNA_define_lib_overridable(false);
+}
+
 void RNA_def_modifier(BlenderRNA *brna)
 {
   StructRNA *srna;
@@ -7266,6 +7354,7 @@ void RNA_def_modifier(BlenderRNA *brna)
 #  endif
   rna_def_modifier_mesh_to_volume(brna);
   rna_def_modifier_volume_displace(brna);
+  rna_def_modifier_volume_to_mesh(brna);
 }
 
 #endif