Jonas Ådahl authored Nov 29, 2024 and Marge Bot committed Dec 05, 2024

clutter_stage_schedule_update() sets the field `update_scheduled` to
`TRUE` as an optimization to make redundant updates a no-op. This failed
if there was a pending event and if the stage was not yet mapped.

What happened is:

 * clutter_stage_schedule_update() is called
   - ClutterStage::update_scheduled is set to TRUE
   - frame clock scheduled
 * frame clock dispatches
   - frame is discarded early, no actual stage update happens
 * device is created (e.g. virtual device from remote desktop session)
   - `device-added` event reaches ClutterStage::event_queue
 * stage is shown
   - clutter_stage_schedule_update() is called
     - ClutterStage::update_scheduled is TRUE
     - ClutterStage::event_queue has events in it
     - These two conditions means clutter_schedule_update() becomes a
       no-op

At this point, no more updates will happen from
clutter_stage_schedule_update().

Fix this by resetting `ClutterStage::update_scheduled` to `FALSE` even
if the frame was discarded due to the stage not yet being mapped.

A test case is added that replicates the above descibed events.

Closes: #3804
Part-of: <!4152>