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

1 files changed, 113 insertions, 0 deletions

diff --git a/source/blender/editors/object/object_modifier.c b/source/blender/editors/object/object_modifier.c
index 1b662ccc389..938ae1f52bf 100644
--- a/source/blender/editors/object/object_modifier.c
+++ b/source/blender/editors/object/object_modifier.c
@@ -1739,6 +1739,119 @@ 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
  * \{ */