TrafficControl: Locking Tracks for Trains - Tests and Visualization - QML

The visualization of locks in QML will be dynamic, with a green/red dot at the start/end station if the track is locked:.

• FREE: If the track is free, no dots will be shown. The track will be green. 
• END/START: If the track is locked in both directions, red dots will be shown at both end and start station. The track will be red.
• LOCKED: If the track is locked at start or end station side, a red dot will appear near that station and a green dot will appear at the eother station. The track will be yellow.

When the lock status is changed. a signal is sent to QML with the new state of the track.

If the state goes from FREE to any other state, two dots are created close to the start and end station. To avoid overlayed dots, the QML part will search the QML tree for existing dots and add new signal dots only if there are no existing dotsfor that particular track..

If the last train leaves a track, that track will be set to FREE and the corresponding signal dots will be removed in QML.

When removing QML items, it takes some time for those changes to take place. That caused some strange behaviour when a train arrived to a station, where another train is waiting for the same track:
Train 1 arrives to station 1 from track 1, existing dots are removed from track 1.
Train 2 enters track 1. QML looks for signal dots for track 1 and finds them as the removal is still in process. The signal dots are repainted.
The signal dots for the track 1 are finally removed.