Fix T100280: GG not toggling the offset transform mode in tracker

Caused by {rB791bfae1d64b}.

The solution was to create the special handle for the Move Clip and Mask
transformation.

One change that cannot be reversed is showing the `G` shortcut in the
statusbar.

But the description of this shortcut was not even correct before.

4 files changed, 30 insertions, 7 deletions

diff --git a/source/blender/editors/transform/transform.c b/source/blender/editors/transform/transform.c
index 7567fd0a91d..bb1776e2756 100644
--- a/source/blender/editors/transform/transform.c
+++ b/source/blender/editors/transform/transform.c
@@ -1008,13 +1008,6 @@ int transformEvent(TransInfo *t, const wmEvent *event)
             t->redraw |= TREDRAW_HARD;
             handled = true;
           }
-          else if (t->options & (CTX_MOVIECLIP | CTX_MASK)) {
-            restoreTransObjects(t);
-
-            t->flag ^= T_ALT_TRANSFORM;
-            t->redraw |= TREDRAW_HARD;
-            handled = true;
-          }
         }
         else {
           if (t->mode == TFM_TRANSLATION) {
diff --git a/source/blender/editors/transform/transform_mode_resize.c b/source/blender/editors/transform/transform_mode_resize.c
index 1ccda96fecb..309b8759320 100644
--- a/source/blender/editors/transform/transform_mode_resize.c
+++ b/source/blender/editors/transform/transform_mode_resize.c
@@ -287,6 +287,7 @@ void initResize(TransInfo *t, float mouse_dir_constraint[3])
 {
   t->mode = TFM_RESIZE;
   t->transform = applyResize;
+  t->handleEvent = NULL;
   t->tsnap.applySnap = ApplySnapResize;
   t->tsnap.distance = ResizeBetween;
 
diff --git a/source/blender/editors/transform/transform_mode_rotate.c b/source/blender/editors/transform/transform_mode_rotate.c
index a7207b36578..ece9fe8855f 100644
--- a/source/blender/editors/transform/transform_mode_rotate.c
+++ b/source/blender/editors/transform/transform_mode_rotate.c
@@ -351,6 +351,7 @@ void initRotation(TransInfo *t)
 
   t->mode = TFM_ROTATION;
   t->transform = applyRotation;
+  t->handleEvent = NULL;
   t->transform_matrix = applyRotationMatrix;
   t->tsnap.applySnap = ApplySnapRotation;
   t->tsnap.distance = RotationBetween;
diff --git a/source/blender/editors/transform/transform_mode_translate.c b/source/blender/editors/transform/transform_mode_translate.c
index 04a41814b53..c4f3d5575cd 100644
--- a/source/blender/editors/transform/transform_mode_translate.c
+++ b/source/blender/editors/transform/transform_mode_translate.c
@@ -56,6 +56,8 @@ struct TranslateCustomData {
   struct {
     enum eTranslateRotateMode rotate_mode;
   } prev;
+
+  const wmKeyMapItem *move_kmi;
 };
 
 /** \} */
@@ -170,6 +172,27 @@ static void transdata_elem_translate_fn(void *__restrict iter_data_v,
 /** \} */
 
 /* -------------------------------------------------------------------- */
+/** \name Events to Move Clip and Mask
+ * \{ */
+
+static eRedrawFlag translate_handleEvent(struct TransInfo *t, const wmEvent *event)
+{
+  BLI_assert(t->options & (CTX_MOVIECLIP | CTX_MASK));
+  struct TranslateCustomData *custom_data = t->custom.mode.data;
+  const wmKeyMapItem *kmi = custom_data->move_kmi;
+  if (kmi && event->type == kmi->type && event->val == kmi->val) {
+    /* Toggles the handle offset effect. */
+    restoreTransObjects(t);
+
+    t->flag ^= T_ALT_TRANSFORM;
+    return TREDRAW_HARD;
+  }
+  return TREDRAW_NOTHING;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
 /** \name Transform (Translation)
  * \{ */
 
@@ -620,6 +643,11 @@ void initTranslation(TransInfo *t)
   custom_data->prev.rotate_mode = TRANSLATE_ROTATE_OFF;
   t->custom.mode.data = custom_data;
   t->custom.mode.use_free = true;
+
+  if (t->keymap && (t->options & (CTX_MOVIECLIP | CTX_MASK))) {
+    custom_data->move_kmi = WM_modalkeymap_find_propvalue(t->keymap, TFM_MODAL_TRANSLATE);
+    t->handleEvent = translate_handleEvent;
+  }
 }
 
 /** \} */