- used quaternion slerp through shortest angle for non full replace blends to fix issue of rotation through longer angle. Unsure if animator ever wants the opposite. If so, that makes things a bit more complicated for specifying which nla channels should have it applied.

1 files changed, 50 insertions, 3 deletions

diff --git a/source/blender/blenkernel/intern/anim_sys.c b/source/blender/blenkernel/intern/anim_sys.c
index 96613de471d..17cf8423b12 100644
--- a/source/blender/blenkernel/intern/anim_sys.c
+++ b/source/blender/blenkernel/intern/anim_sys.c
@@ -2987,9 +2987,56 @@ static void nlaeval_snapshot_blend(NlaEvalData *nlaeval,
       }
     }
     else {
-      for (int j = 0; j < c_lower->length; j++) {
-        c_lower->values[j] = nla_blend_value(
-            upper_blendmode, c_lower->values[j], c_upper->values[j], upper_influence);
+
+      {
+        // blend, user quat slerp through shortest angle if non full replace.
+        // combine and the other blend modes shouldnt need this behavior since replace
+        // defines an absolute orientation while the others are offset and proportional types.
+        if (upper_blendmode == NLASTRIP_MODE_REPLACE && upper_influence < 1.0f) {
+          PropertySubType subtype = RNA_property_subtype(nec->key.prop);
+          int length = nec->base_snapshot.length;
+
+          if (subtype == PROP_QUATERNION && length == 4) {
+            // Todo: quaternion slerp through shorter angle
+            float lower_qt[4], upper_qt[4];
+            copy_qt_qt(upper_qt, c_upper->values);
+            copy_qt_qt(lower_qt, c_lower->values);
+
+            float result_qt[4];
+            interp_qt_qtqt(result_qt, lower_qt, upper_qt, upper_influence);
+
+            copy_qt_qt(c_lower->values, result_qt);
+            continue;
+          }
+          else if (subtype == PROP_AXISANGLE && length == 4) {
+            // Todo: quaternion slerp through shorter angle
+            float lower_qt[4], upper_qt[4];
+            axis_angle_to_quat(upper_qt, c_upper->values, c_upper->values[3]);
+            axis_angle_to_quat(lower_qt, c_lower->values, c_lower->values[3]);
+
+            float result_qt[4];
+            interp_qt_qtqt(result_qt, lower_qt, upper_qt, upper_influence);
+
+            quat_to_axis_angle(c_lower->values, &c_lower->values[3], result_qt);
+            continue;
+          }
+          else if (subtype == PROP_EULER && length == 3) {
+            // Todo: quaternion slerp through shorter angle
+            float lower_qt[4], upper_qt[4];
+            eul_to_quat(upper_qt, c_upper->values);
+            eul_to_quat(lower_qt, c_lower->values);
+
+            float result_qt[4];
+            interp_qt_qtqt(result_qt, lower_qt, upper_qt, upper_influence);
+
+            quat_to_eul(c_lower->values, result_qt);
+            continue;
+          }
+        }
+        for (int j = 0; j < c_lower->length; j++) {
+          c_lower->values[j] = nla_blend_value(
+              upper_blendmode, c_lower->values[j], c_upper->values[j], upper_influence);
+        }
       }
     }
   }