Fix View Roll failure to align the quaternion to the view-axis

View roll checked if the resulting roll was close to a view axis
but didn't write the aligned quaternion back to the final result.
Add ED_view3d_quat_to_axis_view_and_reset_quat since most callers
to ED_view3d_quat_to_axis_view will reset the quaternion when a view
aligned axis is found.

4 files changed, 27 insertions, 9 deletions

diff --git a/source/blender/editors/include/ED_view3d.h b/source/blender/editors/include/ED_view3d.h
index 1e9b68c0920..51fd8e6c533 100644
--- a/source/blender/editors/include/ED_view3d.h
+++ b/source/blender/editors/include/ED_view3d.h
@@ -1064,6 +1064,16 @@ bool ED_view3d_quat_to_axis_view(const float viewquat[4],
                                  float epsilon,
                                  char *r_view,
                                  char *r_view_axis_rotation);
+/**
+ * A version of #ED_view3d_quat_to_axis_view that updates `viewquat`
+ * if it's within `epsilon` to an axis-view.
+ *
+ * \note Include the special case function since most callers need to perform these operations.
+ */
+bool ED_view3d_quat_to_axis_view_and_reset_quat(float viewquat[4],
+                                                float epsilon,
+                                                char *r_view,
+                                                char *r_view_axis_rotation);
 
 char ED_view3d_lock_view_from_index(int index);
 char ED_view3d_axis_view_opposite(char view);
diff --git a/source/blender/editors/space_view3d/view3d_navigate_roll.c b/source/blender/editors/space_view3d/view3d_navigate_roll.c
index ea21eed6445..087ca72211e 100644
--- a/source/blender/editors/space_view3d/view3d_navigate_roll.c
+++ b/source/blender/editors/space_view3d/view3d_navigate_roll.c
@@ -48,11 +48,7 @@ static void view_roll_angle(ARegion *region,
   normalize_qt(quat);
 
   if (use_axis_view && RV3D_VIEW_IS_AXIS(rv3d->view) && (fabsf(angle) == (float)M_PI_2)) {
-    if (ED_view3d_quat_to_axis_view(quat, 0.01f, &rv3d->view, &rv3d->view_axis_roll)) {
-      if (rv3d->view != RV3D_VIEW_USER) {
-        ED_view3d_quat_from_axis_view(rv3d->view, rv3d->view_axis_roll, quat_mul);
-      }
-    }
+    ED_view3d_quat_to_axis_view_and_reset_quat(quat, 0.01f, &rv3d->view, &rv3d->view_axis_roll);
   }
   else {
     rv3d->view = RV3D_VIEW_USER;
diff --git a/source/blender/editors/space_view3d/view3d_navigate_rotate.c b/source/blender/editors/space_view3d/view3d_navigate_rotate.c
index c9ef6422982..989fa152acc 100644
--- a/source/blender/editors/space_view3d/view3d_navigate_rotate.c
+++ b/source/blender/editors/space_view3d/view3d_navigate_rotate.c
@@ -162,10 +162,8 @@ static void viewrotate_apply_snap(ViewOpsData *vod)
 
     if (found) {
       /* lock 'quat_best' to an axis view if we can */
-      ED_view3d_quat_to_axis_view(quat_best, 0.01f, &rv3d->view, &rv3d->view_axis_roll);
-      if (rv3d->view != RV3D_VIEW_USER) {
-        ED_view3d_quat_from_axis_view(rv3d->view, rv3d->view_axis_roll, quat_best);
-      }
+      ED_view3d_quat_to_axis_view_and_reset_quat(
+          quat_best, 0.01f, &rv3d->view, &rv3d->view_axis_roll);
     }
     else {
       copy_qt_qt(quat_best, viewquat_align);
diff --git a/source/blender/editors/space_view3d/view3d_utils.c b/source/blender/editors/space_view3d/view3d_utils.c
index e6895c0f4a3..dd0d5966a76 100644
--- a/source/blender/editors/space_view3d/view3d_utils.c
+++ b/source/blender/editors/space_view3d/view3d_utils.c
@@ -1333,6 +1333,20 @@ bool ED_view3d_quat_to_axis_view(const float quat[4],
   return false;
 }
 
+bool ED_view3d_quat_to_axis_view_and_reset_quat(float quat[4],
+                                                const float epsilon,
+                                                char *r_view,
+                                                char *r_view_axis_roll)
+{
+  const bool is_axis_view = ED_view3d_quat_to_axis_view(quat, epsilon, r_view, r_view_axis_roll);
+  if (is_axis_view) {
+    /* Reset `quat` to it's view axis, so axis-aligned views are always *exactly* aligned. */
+    BLI_assert(*r_view != RV3D_VIEW_USER);
+    ED_view3d_quat_from_axis_view(*r_view, *r_view_axis_roll, quat);
+  }
+  return is_axis_view;
+}
+
 char ED_view3d_lock_view_from_index(int index)
 {
   switch (index) {