Fix bug #21257: make skip AI mid-movement animations invisible and only enable at end.

changelog

@@ -46,6 +46,7 @@ Version 1.11.11+dev:
      menu actions. An actual fix of the bug requires refactoring of the
      animation code which will happen in Wesnoth 1.13.
    * OS X user data directory is now ~/Library/Application Support/Wesnoth_1.12
+   * Fix bug #21257: Lagging animations with skip AI animations and fog/shroud.
 
 Version 1.11.11:
  * Add-ons server:

src/unit_display.cpp

@@ -308,10 +308,17 @@ void unit_mover::start(unit& u)
  */
 void unit_mover::proceed_to(unit& u, size_t path_index, bool update, bool wait)
 {
-	// Nothing to do here if animations can/should not be shown.
-	if ( !can_draw_  || !animate_ )
+	// Nothing to do here if animations cannot be shown.
+	if ( !can_draw_ )
 		return;
 
+	// If no animation then hide unit until end of movement
+	if (!animate_)
+	{
+		u.set_hidden(true);
+		return;
+	}
+
 	// Handle pending visibility issues before introducing new ones.
 	wait_for_anims();
 
@@ -454,6 +461,11 @@ void unit_mover::finish(unit &u, map_location::DIRECTION dir)
 			mousehandler->invalidate_reachmap();
 		}
 	}
+	else
+	{
+		// Show the unit at end of skipped animation
+		u.set_hidden(was_hidden_);
+	}
 
 	// Facing gets set even when not animating.
 	u.set_facing(dir == map_location::NDIRECTIONS ? final_dir : dir);