[Bf-blender-cvs] [6ed581c1079] blender2.8: Multires: Allow changing sculpt level without loosing data

[Sergey Sharybin]

Commit: 6ed581c10794150b0e97725e0d85a88a1ef87f35
Author: Sergey Sharybin
Date:   Tue Sep 25 12:31:01 2018 +0200
Branches: blender2.8
https://developer.blender.org/rB6ed581c10794150b0e97725e0d85a88a1ef87f35

Multires: Allow changing sculpt level without loosing data

As the comment states, this is not really great solution, but
is good enough for now. Proper solution needs some more work,
and maybe reconsideration of what is stored where.

===================================================================

M	source/blender/blenkernel/intern/object.c

===================================================================

diff --git a/source/blender/blenkernel/intern/object.c b/source/blender/blenkernel/intern/object.c
index cdf5af66dd6..0c1da652d0d 100644
--- a/source/blender/blenkernel/intern/object.c
+++ b/source/blender/blenkernel/intern/object.c
@@ -117,6 +117,7 @@
 #include "BKE_speaker.h"
 #include "BKE_softbody.h"
 #include "BKE_subsurf.h"
+#include "BKE_subdiv_ccg.h"
 #include "BKE_material.h"
 #include "BKE_camera.h"
 #include "BKE_image.h"
@@ -339,6 +340,92 @@ void BKE_object_link_modifiers(Scene *scene, struct Object *ob_dst, const struct
 	/* TODO: smoke?, cloth? */
 }
 
+/* Copy CCG related data. Used to sync copy of mesh with reshaped original
+ * mesh.
+ */
+static void copy_ccg_data(Mesh *mesh_destination,
+                          Mesh *mesh_source,
+                          int layer_type)
+{
+	BLI_assert(mesh_destination->totloop == mesh_source->totloop);
+	CustomData *data_destination = &mesh_destination->ldata;
+	CustomData *data_source = &mesh_source->ldata;
+	const int num_elements = mesh_source->totloop;
+	if (!CustomData_has_layer(data_source, layer_type)) {
+		return;
+	}
+	const int layer_index = CustomData_get_layer_index(
+	        data_destination, layer_type);
+	CustomData_free_layer(
+	        data_destination, layer_type, num_elements, layer_index);
+	BLI_assert(!CustomData_has_layer(data_destination, layer_type));
+	CustomData_add_layer(
+	        data_destination, layer_type, CD_CALLOC, NULL, num_elements);
+	BLI_assert(CustomData_has_layer(data_destination, layer_type));
+	CustomData_copy_layer_type_data(data_source, data_destination,
+	                                layer_type, 0, 0, num_elements);
+}
+
+static void object_update_from_subsurf_ccg(Object *object)
+{
+	/* Currently CCG is only created for Mesh objects. */
+	if (object->type != OB_MESH) {
+		return;
+	}
+	/* Object was never evaluated, so can not have CCG subdivision surface. */
+	Mesh *mesh_eval = object->runtime.mesh_eval;
+	if (mesh_eval == NULL) {
+		return;
+	}
+	SubdivCCG *subdiv_ccg = mesh_eval->runtime.subdiv_ccg;
+	if (subdiv_ccg == NULL) {
+		return;
+	}
+	/* Check whether there is anything to be reshaped. */
+	if (!subdiv_ccg->dirty.coords && !subdiv_ccg->dirty.hidden) {
+		return;
+	}
+	Object *object_orig = DEG_get_original_object(object);
+	Mesh *mesh_orig = (Mesh *)object_orig->data;
+	multiresModifier_reshapeFromCCG(6, mesh_orig, subdiv_ccg);
+	/* NOTE: we need to reshape into an original mesh from main database,
+	 * allowing:
+	 *
+	 *  - Update copies of that mesh at any moment.
+	 *  - Save the file without doing extra reshape.
+	 *  - All the users of the mesh have updated displacement.
+	 *
+	 * However, the tricky part here is that we only know about sculpted
+	 * state of a mesh on an object level, and object is being updated after
+	 * mesh datablock is updated. This forces us to:
+	 *
+	 *  - Update mesh datablock from object evaluation, which is technically
+	 *    forbidden, but there is no other place for this yet.
+	 *  - Reshape to the original mesh from main database, and then copy updated
+	 *    layer to copy of that mesh (since copy of the mesh has decoupled
+	 *    custom data layers).
+	 *
+	 * All this is defeating all the designs we need to follow to allow safe
+	 * threaded evaluation, but this is as good as we can make it within the
+	 * current sculpt//evaluated mesh design. This is also how we've survived
+	 * with old DerivedMesh based solutions. So, while this is all wrong and
+	 * needs reconsideration, doesn't seem to be a big stopper for real
+	 * production artists.
+	 */
+	/* TODO(sergey): Solve this somehow, to be fully stable for threaded
+	 * evaluation environment.
+	 */
+	/* NOTE: runtime.mesh_orig is what was before assigning mesh_eval,
+	 * it is orig as in what was in object_eval->data before evaluating
+	 * modifier stack.
+	 *
+	 * mesh_cow is a copy-on-written version od object_orig->data.
+	 */
+	Mesh *mesh_cow = object->runtime.mesh_orig;
+	copy_ccg_data(mesh_cow, mesh_orig, CD_MDISPS);
+	copy_ccg_data(mesh_cow, mesh_orig, CD_GRID_PAINT_MASK);
+}
+
 /* free data derived from mesh, called when mesh changes or is freed */
 void BKE_object_free_derived_caches(Object *ob)
 {
@@ -368,6 +455,7 @@ void BKE_object_free_derived_caches(Object *ob)
 		ob->bb = NULL;
 	}
 
+	object_update_from_subsurf_ccg(ob);
 	BKE_object_free_derived_mesh_caches(ob);
 
 	if (ob->runtime.mesh_eval != NULL) {