Fix T101522: Animation: motion path range overwritten by 'Update Paths'

Expand the motion path frame range options with an extra option "Manual
Range". When chosen, Blender will not automatically update the path
range any more.

Additionally, the start/end frame fields are greyed out in the UI when
one of the automatic range options is selected (i.e. all but the new
"Manual Range" one). It is still possible to set the start/end frame
temporarily, but the original behaviour (of recomputing those on update)
remains.

Manifest Task: T101522

release/scripts/startup/bl_ui/properties_animviz.py

@@ -32,8 +32,10 @@ class MotionPathButtonsPanel:
             col.prop(mps, "frame_step", text="Step")
         elif mps.type == 'RANGE':
             col = layout.column(align=True)
-            col.prop(mps, "frame_start", text="Frame Range Start")
-            col.prop(mps, "frame_end", text="End")
+            start_end_group = col.column(align=True)
+            start_end_group.active = mps.range == 'MANUAL'
+            start_end_group.prop(mps, "frame_start", text="Frame Range Start")
+            start_end_group.prop(mps, "frame_end", text="End")
             col.prop(mps, "frame_step", text="Step")
 
         # Calculation Range

source/blender/editors/animation/anim_motion_paths.c

@@ -344,9 +344,16 @@ void animviz_motionpath_compute_range(Object *ob, Scene *scene)
 {
   bAnimVizSettings *avs = ob->mode == OB_MODE_POSE ? &ob->pose->avs : &ob->avs;
 
+  if (avs->path_range == MOTIONPATH_RANGE_MANUAL) {
+    /* Don't touch manually-determined ranges.  */
+    return;
+  }
+
   const bool has_action = ob->adt && ob->adt->action;
   if (avs->path_range == MOTIONPATH_RANGE_SCENE || !has_action ||
       BLI_listbase_is_empty(&ob->adt->action->curves)) {
+    /* Default to the scene (preview) range if there is no animation data to
+     * find selected keys in. */
     avs->path_sf = PSFRA;
     avs->path_ef = PEFRA;
     return;
@@ -367,6 +374,7 @@ void animviz_motionpath_compute_range(Object *ob, Scene *scene)
     case MOTIONPATH_RANGE_KEYS_ALL:
       ED_keylist_all_keys_frame_range(keylist, &frame_range);
       break;
+    case MOTIONPATH_RANGE_MANUAL:
     case MOTIONPATH_RANGE_SCENE:
       BLI_assert_msg(false, "This should not happen, function should have exited earlier.");
   };

source/blender/makesdna/DNA_action_types.h

@@ -139,6 +139,7 @@ typedef enum eMotionPath_Ranges {
   MOTIONPATH_RANGE_SCENE = 0,
   MOTIONPATH_RANGE_KEYS_SELECTED = 1,
   MOTIONPATH_RANGE_KEYS_ALL = 2,
+  MOTIONPATH_RANGE_MANUAL = 3,
 } eMotionPath_Ranges;
 
 /* bAnimVizSettings->path_viewflag */

source/blender/makesrna/intern/rna_animviz.c

@@ -58,6 +58,7 @@ const EnumPropertyItem rna_enum_motionpath_range_items[] = {
      "Selected Keys",
      "From the first selected keyframe to the last"},
     {MOTIONPATH_RANGE_SCENE, "SCENE", 0, "Scene Frame Range", "The entire Scene / Preview range"},
+    {MOTIONPATH_RANGE_MANUAL, "MANUAL", 0, "Manual Range", "Manually determined frame range"},
     {0, NULL, 0, NULL, NULL},
 };