Python: Expose crazyspace correction functionality via RNA

Allows to perform correction of coordinate delta/displacement in a
similar way of how sculpt mode handles sculpting on a deformed mesh.
An example of usecase of this is allowing riggers and sciprters to
improve corrective shapekey workflow.

The usage consists of pre-processing and access. For example:

  object.crazyspace_eval(depsgraph, scene)

  # When we have a difference between two vertices and want to convert
  # it to a space to be stored, say, in shapekey:
  delta_in_orig_space = rigged_ob.crazyspace_displacement_to_original(
      vertex_index=i, displacement=delta)

  # The reverse of above.
  delta_in_deformed_space = rigged_ob.crazyspace_displacement_to_deformed(
      vertex_index=i, displacement=delta)

  object.crazyspace_eval_clear()

Fuller explanation with actual usecases and studio examples are written in
the comment:

  https://developer.blender.org/D13892#368898

Differential Revision: https://developer.blender.org/D13892

2 files changed, 89 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/crazyspace.c b/source/blender/blenkernel/intern/crazyspace.c
index 9408b9190ae..573595b6f90 100644
--- a/source/blender/blenkernel/intern/crazyspace.c
+++ b/source/blender/blenkernel/intern/crazyspace.c
@@ -41,6 +41,7 @@
 #include "BKE_mesh_wrapper.h"
 #include "BKE_modifier.h"
 #include "BKE_multires.h"
+#include "BKE_report.h"
 
 #include "DEG_depsgraph_query.h"
 
@@ -516,3 +517,85 @@ void BKE_crazyspace_build_sculpt(struct Depsgraph *depsgraph,
     }
   }
 }
+
+/* -------------------------------------------------------------------- */
+/** \name Crazyspace API
+ * \{ */
+
+void BKE_crazyspace_api_eval(Depsgraph *depsgraph,
+                             Scene *scene,
+                             Object *object,
+                             struct ReportList *reports)
+{
+  if (object->runtime.crazyspace_deform_imats != NULL ||
+      object->runtime.crazyspace_deform_cos != NULL) {
+    return;
+  }
+
+  if (object->type != OB_MESH) {
+    BKE_report(reports,
+               RPT_ERROR,
+               "Crazyspace transformation is only available for Mesh type of objects");
+    return;
+  }
+
+  const Mesh *mesh = (const Mesh *)object->data;
+  object->runtime.crazyspace_num_verts = mesh->totvert;
+  BKE_crazyspace_build_sculpt(depsgraph,
+                              scene,
+                              object,
+                              &object->runtime.crazyspace_deform_imats,
+                              &object->runtime.crazyspace_deform_cos);
+}
+
+void BKE_crazyspace_api_displacement_to_deformed(struct Object *object,
+                                                 struct ReportList *reports,
+                                                 int vertex_index,
+                                                 float displacement[3],
+                                                 float r_displacement_deformed[3])
+{
+  if (vertex_index < 0 || vertex_index >= object->runtime.crazyspace_num_verts) {
+    BKE_reportf(reports,
+                RPT_ERROR,
+                "Invalid vertex index %d (expected to be within 0 to %d range)",
+                vertex_index,
+                object->runtime.crazyspace_num_verts);
+    return;
+  }
+
+  mul_v3_m3v3(r_displacement_deformed,
+              object->runtime.crazyspace_deform_imats[vertex_index],
+              displacement);
+}
+
+void BKE_crazyspace_api_displacement_to_original(struct Object *object,
+                                                 struct ReportList *reports,
+                                                 int vertex_index,
+                                                 float displacement_deformed[3],
+                                                 float r_displacement[3])
+{
+  if (vertex_index < 0 || vertex_index >= object->runtime.crazyspace_num_verts) {
+    BKE_reportf(reports,
+                RPT_ERROR,
+                "Invalid vertex index %d (expected to be within 0 to %d range))",
+                vertex_index,
+                object->runtime.crazyspace_num_verts);
+    return;
+  }
+
+  float mat[3][3];
+  if (!invert_m3_m3(mat, object->runtime.crazyspace_deform_imats[vertex_index])) {
+    copy_v3_v3(r_displacement, displacement_deformed);
+    return;
+  }
+
+  mul_v3_m3v3(r_displacement, mat, displacement_deformed);
+}
+
+void BKE_crazyspace_api_eval_clear(Object *object)
+{
+  MEM_SAFE_FREE(object->runtime.crazyspace_deform_imats);
+  MEM_SAFE_FREE(object->runtime.crazyspace_deform_cos);
+}
+
+/** \} */
diff --git a/source/blender/blenkernel/intern/object.cc b/source/blender/blenkernel/intern/object.cc
index 3fa380d2519..ed0174bd592 100644
--- a/source/blender/blenkernel/intern/object.cc
+++ b/source/blender/blenkernel/intern/object.cc
@@ -87,6 +87,7 @@
 #include "BKE_camera.h"
 #include "BKE_collection.h"
 #include "BKE_constraint.h"
+#include "BKE_crazyspace.h"
 #include "BKE_curve.h"
 #include "BKE_deform.h"
 #include "BKE_displist.h"
@@ -1881,6 +1882,8 @@ void BKE_object_free_derived_caches(Object *ob)
   BKE_object_to_curve_clear(ob);
   BKE_object_free_curve_cache(ob);
 
+  BKE_crazyspace_api_eval_clear(ob);
+
   /* Clear grease pencil data. */
   if (ob->runtime.gpd_eval != nullptr) {
     BKE_gpencil_eval_delete(ob->runtime.gpd_eval);
@@ -5219,6 +5222,9 @@ void BKE_object_runtime_reset_on_copy(Object *object, const int UNUSED(flag))
   runtime->object_as_temp_mesh = nullptr;
   runtime->object_as_temp_curve = nullptr;
   runtime->geometry_set_eval = nullptr;
+
+  runtime->crazyspace_deform_imats = nullptr;
+  runtime->crazyspace_deform_cos = nullptr;
 }
 
 void BKE_object_runtime_free_data(Object *object)