[Bugfix] line_alternators reset scroll state without new data

this is fallout from allowing a scroll item redisplay timeouts

prior to eb3e5eb  '[Feature] skinengine subline timeout hide line for n seconds'
the behavior could be seen sparingly
after we now have an alternator front and center with the next track scroll

unfortunately this results in strings never scrolling to completion

fix:
if the current line hasn't changed and we are not doing a
full screen refresh, don't invalidate the scroll viewport
(the scroll engine will still handle the user data changing
 if that actually occurred)

Change-Id: I10d4b8a05caa28de617dc6454520ce5426d69532

1 files changed, 7 insertions, 3 deletions

diff --git a/apps/gui/skin_engine/skin_render.c b/apps/gui/skin_engine/skin_render.c
index 8431a68894..e8e3506778 100644
--- a/apps/gui/skin_engine/skin_render.c
+++ b/apps/gui/skin_engine/skin_render.c
@@ -712,14 +712,18 @@ bool skin_render_alternator(struct skin_element* element, struct skin_draw_info
         }
         while (try_line != start && !suitable);
 
+        if (info->refresh_type == SKIN_REFRESH_ALL
+            || try_line != alternator->current_line)
+        {
+            info->force_redraw = true;
+        }
+        info->refresh_type = SKIN_REFRESH_ALL;
+
         if (suitable)
         {
             alternator->current_line = try_line;
             alternator->next_change_tick = current_tick + rettimeout;
         }
-
-        info->refresh_type = SKIN_REFRESH_ALL;
-        info->force_redraw = true;
     }
     bool ret = skin_render_line(get_child(element->children, alternator->current_line), info);
     info->refresh_type = old_refresh;