UI: Add Transitions to arcade GUI [after 3.0 release]

[eruvanos]

This adds an easy way to animate UIWidgets.

Implemented transitions:

• TransitionAttr - Change value over time (start til end)
• TransitionAttrIncr - Increment value over time
• TransitionAttrSet - Set value after time
• TransitionParallel - Execute multiple transactions parallel
• TransitionChain - Execute multiple transactions sequentially
• TransitionDelay - Used to pause :class:TransitionChain

widget = UIWidget()
# move a widgets center_x from 0 to 100 within 2 seconds
widget.add_transition(Transition(attribute="center_x", start=0, end=100, duration=2))

The transition implementation could also be used with sprites, I am not sure which way would be a good one. I would love to get some feedback.

I see two options:

# add transition
sprite.add_transition(Transition(...))

# integrate transition update in sprite updates
sprite.on_update()

or

# use a `Animation` class to connect a sprite and a transition
animation = Animation(sprite, Transition())

# update transitions via an wrapping `Animation` object
animation.on_update(dt)

[eruvanos]

Talked to @einarf :

• missing feature: cancel transition
• for Sprites, this might be a performance problem

[eruvanos]

Will be added after 3.0 release. It is more important to release!