1 files changed, 50 insertions, 18 deletions

diff --git a/source/blender/blenkernel/intern/fcurve.c b/source/blender/blenkernel/intern/fcurve.c
index ef53c926daa..c4da2d2efc9 100644
--- a/source/blender/blenkernel/intern/fcurve.c
+++ b/source/blender/blenkernel/intern/fcurve.c
@@ -1732,35 +1732,21 @@ static float dvar_eval_transChan(ChannelDriver *driver, DriverVar *dvar)
      *         - only an option for "transform space", if quality is really bad with a)
      */
     float quat[4];
-    float *const eul = quat + 1;
     int channel;
 
     if (dtar->transChan == DTAR_TRANSCHAN_ROTW) {
       channel = 0;
-      quat[0] = 0.0f;
     }
     else {
       channel = 1 + dtar->transChan - DTAR_TRANSCHAN_ROTX;
       BLI_assert(channel < 4);
     }
 
-    if (dtar->rotation_mode == DTAR_ROTMODE_AUTO) {
-      mat4_to_eulO(eul, rot_order, mat);
+    BKE_driver_target_matrix_to_rot_channels(
+        mat, rot_order, dtar->rotation_mode, channel, false, quat);
 
-      if (use_eulers) {
-        compatible_eul(eul, oldEul);
-      }
-    }
-    else if (dtar->rotation_mode >= DTAR_ROTMODE_EULER_MIN &&
-             dtar->rotation_mode <= DTAR_ROTMODE_EULER_MAX) {
-      mat4_to_eulO(eul, dtar->rotation_mode, mat);
-    }
-    else if (dtar->rotation_mode == DTAR_ROTMODE_QUATERNION) {
-      mat4_to_quat(quat, mat);
-    }
-    else {
-      BLI_assert(false);
-      zero_v3(eul);
+    if (use_eulers && dtar->rotation_mode == DTAR_ROTMODE_AUTO) {
+      compatible_eul(quat + 1, oldEul);
     }
 
     return quat[channel];
@@ -1771,6 +1757,52 @@ static float dvar_eval_transChan(ChannelDriver *driver, DriverVar *dvar)
   }
 }
 
+/* Convert a quaternion to pseudo-angles representing the weighted amount of rotation. */
+static void quaternion_to_angles(float quat[4], int channel)
+{
+  if (channel < 0) {
+    quat[0] = 2.0f * saacosf(quat[0]);
+
+    for (int i = 1; i < 4; i++) {
+      quat[i] = 2.0f * saasinf(quat[i]);
+    }
+  }
+  else if (channel == 0) {
+    quat[0] = 2.0f * saacosf(quat[0]);
+  }
+  else {
+    quat[channel] = 2.0f * saasinf(quat[channel]);
+  }
+}
+
+/* Compute channel values for a rotational Transform Channel driver variable. */
+void BKE_driver_target_matrix_to_rot_channels(
+    float mat[4][4], int auto_order, int rotation_mode, int channel, bool angles, float r_buf[4])
+{
+  float *const quat = r_buf;
+  float *const eul = r_buf + 1;
+
+  zero_v4(r_buf);
+
+  if (rotation_mode == DTAR_ROTMODE_AUTO) {
+    mat4_to_eulO(eul, auto_order, mat);
+  }
+  else if (rotation_mode >= DTAR_ROTMODE_EULER_MIN && rotation_mode <= DTAR_ROTMODE_EULER_MAX) {
+    mat4_to_eulO(eul, rotation_mode, mat);
+  }
+  else if (rotation_mode == DTAR_ROTMODE_QUATERNION) {
+    mat4_to_quat(quat, mat);
+
+    /* For Transformation constraint convenience, convert to pseudo-angles. */
+    if (angles) {
+      quaternion_to_angles(quat, channel);
+    }
+  }
+  else {
+    BLI_assert(false);
+  }
+}
+
 /* ......... */
 
 /* Table of Driver Variable Type Info Data */