Multires: Unsubdivide and Rebuild Subdivisions

This implements the main unsubdivide algorithm which rebuilds a base mesh and extracts the grid's data from a high resolution mesh.
It includes the Rebuild Subdivisions operator, which generates all subdivision levels down to the level 0 base mesh.

It supports:
- Rebuilding an arbitrary number of levels (Unsubdivide) or as many levels as possible down to level 0 in a single step (Rebuild Subdivisions).
- Rebuilding with already existing grids.
- Meshes with n-gons and triangles
- Meshes with more than 2 faces per edge
- Base mesh made completely out of triangles
- Meshes without poles
- Meshes with multiple disconnected elements at the same subdivision level

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7372

release/scripts/startup/bl_ui/properties_data_modifier.py

@@ -698,8 +698,10 @@ class DATA_PT_modifiers(ModifierButtonsPanel, Panel):
         col.enabled = ob.mode != 'EDIT'
         col.operator("object.multires_subdivide", text="Subdivide")
         col.operator("object.multires_higher_levels_delete", text="Delete Higher")
+        col.operator("object.multires_unsubdivide", text="Unsubdivide")
         col.operator("object.multires_reshape", text="Reshape")
         col.operator("object.multires_base_apply", text="Apply Base")
+        col.operator("object.multires_rebuild_subdiv", text="Rebuild Subdivisions")
         col.prop(md, "uv_smooth", text="")
         col.prop(md, "show_only_control_edges")
         col.prop(md, "use_creases")

source/blender/blenkernel/BKE_multires.h

@@ -110,6 +110,11 @@ void multiresModifier_del_levels(struct MultiresModifierData *mmd,
 void multiresModifier_base_apply(struct Depsgraph *depsgraph,
                                  struct Object *object,
                                  struct MultiresModifierData *mmd);
+int multiresModifier_rebuild_subdiv(struct Depsgraph *depsgraph,
+                                    struct Object *object,
+                                    struct MultiresModifierData *mmd,
+                                    int rebuild_limit,
+                                    bool switch_view_to_lower_level);
 void multiresModifier_subdivide_legacy(struct MultiresModifierData *mmd,
                                        struct Scene *scene,
                                        struct Object *ob,

source/blender/blenkernel/CMakeLists.txt

@@ -178,6 +178,7 @@ set(SRC
   intern/multires_reshape_util.c
   intern/multires_reshape_vertcos.c
   intern/multires_subdiv.c
+  intern/multires_unsubdivide.c
   intern/nla.c
   intern/node.c
   intern/object.c
@@ -397,6 +398,7 @@ set(SRC
   intern/lib_intern.h
   intern/multires_inline.h
   intern/multires_reshape.h
+  intern/multires_unsubdivide.h
   intern/pbvh_intern.h
   intern/subdiv_converter.h
   intern/subdiv_inline.h

source/blender/blenkernel/intern/multires_reshape.h

@@ -156,6 +156,11 @@ bool multires_reshape_context_create_from_object(MultiresReshapeContext *reshape
                                                  struct Object *object,
                                                  struct MultiresModifierData *mmd);
 
+bool multires_reshape_context_create_from_base_mesh(MultiresReshapeContext *reshape_context,
+                                                    struct Depsgraph *depsgraph,
+                                                    struct Object *object,
+                                                    struct MultiresModifierData *mmd);
+
 bool multires_reshape_context_create_from_ccg(MultiresReshapeContext *reshape_context,
                                               struct SubdivCCG *subdiv_ccg,
                                               struct Mesh *base_mesh,

source/blender/blenkernel/intern/multires_reshape_util.c

@@ -152,6 +152,39 @@ static bool context_verify_or_free(MultiresReshapeContext *reshape_context)
   return is_valid;
 }
 
+bool multires_reshape_context_create_from_base_mesh(MultiresReshapeContext *reshape_context,
+                                                    Depsgraph *depsgraph,
+                                                    Object *object,
+                                                    MultiresModifierData *mmd)
+{
+  context_zero(reshape_context);
+
+  const bool use_render_params = false;
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  Mesh *base_mesh = (Mesh *)object->data;
+
+  reshape_context->depsgraph = depsgraph;
+  reshape_context->object = object;
+  reshape_context->mmd = mmd;
+
+  reshape_context->base_mesh = base_mesh;
+
+  reshape_context->subdiv = multires_reshape_create_subdiv(NULL, object, mmd);
+  reshape_context->need_free_subdiv = true;
+
+  reshape_context->reshape.level = multires_get_level(
+      scene_eval, object, mmd, use_render_params, true);
+  reshape_context->reshape.grid_size = BKE_subdiv_grid_size_from_level(
+      reshape_context->reshape.level);
+
+  reshape_context->top.level = mmd->totlvl;
+  reshape_context->top.grid_size = BKE_subdiv_grid_size_from_level(reshape_context->top.level);
+
+  context_init_commoon(reshape_context);
+
+  return context_verify_or_free(reshape_context);
+}
+
 bool multires_reshape_context_create_from_object(MultiresReshapeContext *reshape_context,
                                                  Depsgraph *depsgraph,
                                                  Object *object,
@@ -272,9 +305,9 @@ void multires_reshape_context_free(MultiresReshapeContext *reshape_context)
 
   multires_reshape_free_original_grids(reshape_context);
 
-  MEM_freeN(reshape_context->face_start_grid_index);
-  MEM_freeN(reshape_context->ptex_start_grid_index);
-  MEM_freeN(reshape_context->grid_to_face_index);
+  MEM_SAFE_FREE(reshape_context->face_start_grid_index);
+  MEM_SAFE_FREE(reshape_context->ptex_start_grid_index);
+  MEM_SAFE_FREE(reshape_context->grid_to_face_index);
 }
 
 /** \} */

source/blender/blenkernel/intern/multires_unsubdivide.h

@@ -0,0 +1,93 @@
+/*
+ * 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.
+ *
+ * The Original Code is Copyright (C) 2020 Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup bke
+ */
+
+#ifndef __BKE_INTERN_MULTIRES_UNSUBDIVIDE_H__
+#define __BKE_INTERN_MULTIRES_UNSUBDIVIDE_H__
+
+#include "BLI_sys_types.h"
+
+struct BMesh;
+struct Depsgraph;
+struct Mesh;
+struct MultiresModifierData;
+struct Object;
+
+typedef struct MultiresUnsubdivideGrid {
+  /* For sanity checks. */
+  int grid_index;
+  int grid_size;
+
+  /* Grid coordinates in object space. */
+  float (*grid_co)[3];
+
+} MultiresUnsubdivideGrid;
+
+typedef struct MultiresUnsubdivideContext {
+  /* Input Mesh to unsubdivide. */
+  struct Mesh *original_mesh;
+  struct MDisps *original_mdisp;
+
+  /* Number of subdivision in the grids of the input mesh. */
+  int num_original_levels;
+
+  /* Level 0 base mesh after applying the maximum amount of unsubdivisions. */
+  struct Mesh *base_mesh;
+
+  /* Limit on how many levels down the unsubdivide operation should create, if possible. */
+  int max_new_levels;
+
+  /* New levels that were created after unsubdividing. */
+  int num_new_levels;
+
+  /* Number of subdivisions that should be applied to the base mesh. (num_new_levels +
+   * num_original_levels)
+   */
+  int num_total_levels;
+
+  /* Data for the new grids, indexed by base mesh loop index. */
+  int num_grids;
+  struct MultiresUnsubdivideGrid *base_mesh_grids;
+
+  /* Private data. */
+  struct BMesh *bm_original_mesh;
+  int *loop_to_face_map;
+  int *base_to_orig_vmap;
+} MultiresUnsubdivideContext;
+
+/* ================================================================================================
+ * Construct/destruct reshape context.
+ */
+
+void multires_unsubdivide_context_init(MultiresUnsubdivideContext *context,
+                                       struct Mesh *original_mesh,
+                                       struct MultiresModifierData *mmd);
+void multires_unsubdivide_context_free(MultiresUnsubdivideContext *context);
+
+/* ================================================================================================
+ * Rebuild Lower Subdivisions.
+ */
+
+/* Rebuilds all subdivision to the level 0 base mesh. */
+bool multires_unsubdivide_to_basemesh(MultiresUnsubdivideContext *context);
+
+#endif /* __BKE_INTERN_MULTIRES_UNSUBDIVIDE_H__ */

source/blender/editors/object/object_intern.h

@@ -169,6 +169,8 @@ void OBJECT_OT_multires_subdivide(struct wmOperatorType *ot);
 void OBJECT_OT_multires_reshape(struct wmOperatorType *ot);
 void OBJECT_OT_multires_higher_levels_delete(struct wmOperatorType *ot);
 void OBJECT_OT_multires_base_apply(struct wmOperatorType *ot);
+void OBJECT_OT_multires_unsubdivide(struct wmOperatorType *ot);
+void OBJECT_OT_multires_rebuild_subdiv(struct wmOperatorType *ot);
 void OBJECT_OT_multires_external_save(struct wmOperatorType *ot);
 void OBJECT_OT_multires_external_pack(struct wmOperatorType *ot);
 void OBJECT_OT_correctivesmooth_bind(struct wmOperatorType *ot);

source/blender/editors/object/object_modifier.c

@@ -1738,6 +1738,119 @@ void OBJECT_OT_multires_base_apply(wmOperatorType *ot)
 
 /** \} */
 
+/* ------------------------------------------------------------------- */
+/** \name Multires Unsubdivide
+ * \{ */
+
+static int multires_unsubdivide_exec(bContext *C, wmOperator *op)
+{
+  Depsgraph *depsgraph = CTX_data_depsgraph_pointer(C);
+  Object *object = ED_object_active_context(C);
+  MultiresModifierData *mmd = (MultiresModifierData *)edit_modifier_property_get(
+      op, object, eModifierType_Multires);
+
+  if (!mmd) {
+    return OPERATOR_CANCELLED;
+  }
+
+  int new_levels = multiresModifier_rebuild_subdiv(depsgraph, object, mmd, 1, true);
+  if (new_levels == 0) {
+    BKE_report(op->reports, RPT_ERROR, "Not valid subdivisions found to rebuild a lower level");
+    return OPERATOR_CANCELLED;
+  }
+
+  DEG_id_tag_update(&object->id, ID_RECALC_GEOMETRY);
+  WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, object);
+
+  return OPERATOR_FINISHED;
+}
+
+static int multires_unsubdivide_invoke(bContext *C, wmOperator *op, const wmEvent *UNUSED(event))
+{
+  if (edit_modifier_invoke_properties(C, op)) {
+    return multires_unsubdivide_exec(C, op);
+  }
+  else {
+    return OPERATOR_CANCELLED;
+  }
+}
+
+void OBJECT_OT_multires_unsubdivide(wmOperatorType *ot)
+{
+  ot->name = "Unsubdivide";
+  ot->description = "Rebuild a lower subdivision level of the current base mesh";
+  ot->idname = "OBJECT_OT_multires_unsubdivide";
+
+  ot->poll = multires_poll;
+  ot->invoke = multires_unsubdivide_invoke;
+  ot->exec = multires_unsubdivide_exec;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+  edit_modifier_properties(ot);
+}
+
+/** \} */
+
+/* ------------------------------------------------------------------- */
+/** \name Multires Rebuild Subdivisions
+ * \{ */
+
+static int multires_rebuild_subdiv_exec(bContext *C, wmOperator *op)
+{
+  Depsgraph *depsgraph = CTX_data_depsgraph_pointer(C);
+  Object *object = ED_object_active_context(C);
+  MultiresModifierData *mmd = (MultiresModifierData *)edit_modifier_property_get(
+      op, object, eModifierType_Multires);
+
+  if (!mmd) {
+    return OPERATOR_CANCELLED;
+  }
+
+  int new_levels = multiresModifier_rebuild_subdiv(depsgraph, object, mmd, INT_MAX, false);
+  if (new_levels == 0) {
+    BKE_report(op->reports, RPT_ERROR, "Not valid subdivisions found to rebuild lower levels");
+    return OPERATOR_CANCELLED;
+  }
+
+  BKE_reportf(op->reports, RPT_INFO, "%d new levels rebuilt", new_levels);
+
+  DEG_id_tag_update(&object->id, ID_RECALC_GEOMETRY);
+  WM_event_add_notifier(C, NC_OBJECT | ND_MODIFIER, object);
+
+  return OPERATOR_FINISHED;
+}
+
+static int multires_rebuild_subdiv_invoke(bContext *C,
+                                          wmOperator *op,
+                                          const wmEvent *UNUSED(event))
+{
+  if (edit_modifier_invoke_properties(C, op)) {
+    return multires_rebuild_subdiv_exec(C, op);
+  }
+  else {
+    return OPERATOR_CANCELLED;
+  }
+}
+
+void OBJECT_OT_multires_rebuild_subdiv(wmOperatorType *ot)
+{
+  ot->name = "Rebuild Lower Subdivisions";
+  ot->description =
+      "Rebuilds all possible subdivisions levels to generate a lower resolution base mesh";
+  ot->idname = "OBJECT_OT_multires_rebuild_subdiv";
+
+  ot->poll = multires_poll;
+  ot->invoke = multires_rebuild_subdiv_invoke;
+  ot->exec = multires_rebuild_subdiv_exec;
+
+  /* flags */
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO | OPTYPE_INTERNAL;
+  edit_modifier_properties(ot);
+}
+
+/** \} */
+
 /* ------------------------------------------------------------------- */
 /** \name Skin Modifier
  * \{ */

source/blender/editors/object/object_ops.c

@@ -137,6 +137,8 @@ void ED_operatortypes_object(void)
   WM_operatortype_append(OBJECT_OT_multires_reshape);
   WM_operatortype_append(OBJECT_OT_multires_higher_levels_delete);
   WM_operatortype_append(OBJECT_OT_multires_base_apply);
+  WM_operatortype_append(OBJECT_OT_multires_unsubdivide);
+  WM_operatortype_append(OBJECT_OT_multires_rebuild_subdiv);
   WM_operatortype_append(OBJECT_OT_multires_external_save);
   WM_operatortype_append(OBJECT_OT_multires_external_pack);
   WM_operatortype_append(OBJECT_OT_skin_root_mark);