Copy Rotation: implement new mixing modes that actually work.

Upon close inspection, the way the Offset mode works in the
Copy Rotation constraint makes no sense, and in fact, destroys
the rotation of its owner unless either it's single axis, or
the order is set specifically to `ZYX Euler`.

Since it can't simply be changed because of backward compatibility
concerns, replace the checkbox with a dropdown that provides a set
of new modes that actually make sense.

Specifically, add a mode that simply adds Euler components together,
and two options that use matrix multiplication in different order.

The Python use_offset property is replaced with compatibility stubs.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D5640

1 files changed, 52 insertions, 2 deletions

diff --git a/source/blender/makesrna/intern/rna_constraint.c b/source/blender/makesrna/intern/rna_constraint.c
index 05154dcc20e..79e38717569 100644
--- a/source/blender/makesrna/intern/rna_constraint.c
+++ b/source/blender/makesrna/intern/rna_constraint.c
@@ -530,6 +530,24 @@ static void rna_Constraint_ik_type_set(struct PointerRNA *ptr, int value)
   }
 }
 
+/* DEPRECATED: use_offset replaced with mix_mode */
+static bool rna_Constraint_RotLike_use_offset_get(struct PointerRNA *ptr)
+{
+  bConstraint *con = ptr->data;
+  bRotateLikeConstraint *rotlike = con->data;
+  return rotlike->mix_mode != ROTLIKE_MIX_REPLACE;
+}
+
+static void rna_Constraint_RotLike_use_offset_set(struct PointerRNA *ptr, bool value)
+{
+  bConstraint *con = ptr->data;
+  bRotateLikeConstraint *rotlike = con->data;
+  bool curval = (rotlike->mix_mode != ROTLIKE_MIX_REPLACE);
+  if (curval != value) {
+    rotlike->mix_mode = (value ? ROTLIKE_MIX_OFFSET : ROTLIKE_MIX_REPLACE);
+  }
+}
+
 static const EnumPropertyItem *rna_Constraint_owner_space_itemf(bContext *UNUSED(C),
                                                                 PointerRNA *ptr,
                                                                 PropertyRNA *UNUSED(prop),
@@ -1298,6 +1316,28 @@ static void rna_def_constraint_rotate_like(BlenderRNA *brna)
   StructRNA *srna;
   PropertyRNA *prop;
 
+  static const EnumPropertyItem mix_mode_items[] = {
+      {ROTLIKE_MIX_REPLACE, "REPLACE", 0, "Replace", "Replace the original rotation with copied"},
+      {ROTLIKE_MIX_ADD, "ADD", 0, "Add", "Add euler component values together"},
+      {ROTLIKE_MIX_BEFORE,
+       "BEFORE",
+       0,
+       "Before Original",
+       "Apply copied rotation before original, as if the constraint target is a parent"},
+      {ROTLIKE_MIX_AFTER,
+       "AFTER",
+       0,
+       "After Original",
+       "Apply copied rotation after original, as if the constraint target is a child"},
+      {ROTLIKE_MIX_OFFSET,
+       "OFFSET",
+       0,
+       "Offset (Legacy)",
+       "Combine rotations like the original Offset checkbox. Does not work well for "
+       "multiple axis rotations"},
+      {0, NULL, 0, NULL, NULL},
+  };
+
   srna = RNA_def_struct(brna, "CopyRotationConstraint", "Constraint");
   RNA_def_struct_ui_text(srna, "Copy Rotation Constraint", "Copy the rotation of the target");
   RNA_def_struct_sdna_from(srna, "bRotateLikeConstraint", "data");
@@ -1341,9 +1381,19 @@ static void rna_def_constraint_rotate_like(BlenderRNA *brna)
   RNA_def_property_ui_text(prop, "Euler Order", "Explicitly specify the euler rotation order");
   RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
 
+  prop = RNA_def_property(srna, "mix_mode", PROP_ENUM, PROP_NONE);
+  RNA_def_property_enum_sdna(prop, NULL, "mix_mode");
+  RNA_def_property_enum_items(prop, mix_mode_items);
+  RNA_def_property_ui_text(
+      prop, "Mix Mode", "Specify how the copied and existing rotations are combined");
+  RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
+
+  /* DEPRECATED: replaced with mix_mode */
   prop = RNA_def_property(srna, "use_offset", PROP_BOOLEAN, PROP_NONE);
-  RNA_def_property_boolean_sdna(prop, NULL, "flag", ROTLIKE_OFFSET);
-  RNA_def_property_ui_text(prop, "Offset", "Add original rotation into copied rotation");
+  RNA_def_property_boolean_funcs(
+      prop, "rna_Constraint_RotLike_use_offset_get", "rna_Constraint_RotLike_use_offset_set");
+  RNA_def_property_ui_text(
+      prop, "Offset", "DEPRECATED: Add original rotation into copied rotation");
   RNA_def_property_update(prop, NC_OBJECT | ND_CONSTRAINT, "rna_Constraint_update");
 }