State Machines

For complex real-time editing possibilities, like what happens in the scenario and the curve, we use the QStateMachine framework.

However due to the complexity of the state machines involved, a typesafe layer is added upon it, which allows to easily have matched events and transitions at no more runtime cost than what Qt offers.

There are default events transitions for the common cases of objects being pressed, moving, released, with an alternate modifier, and a cancel option.

The general pattern relies on multiple encapsulated state machines :

• A top-level one that will handle the current "tool" (move, create, etc...)
• Each tool is a state which encapsulates another state machine. This is because we want to be able to change the active tool while currently doing something in a sub-state, which is not possible if all the states are part of the state machine.

Instead of relying on QGraphicsItem's facilities for knowing if an object is pressed / moved / etc., we use the "itemUnderMouse" method and a switch/case which is faster by a large amount.

Each tool state will then have cases for what happens when an object is entered and left for another object, like ScenarioCreation_FromState for instance.

For simpler cases, see MoveState in the automation plug-in, which currently handles moving a point.