Conditional widgets Stage 1

[p0nce]

The issue is that at this point I have:

• UICondKnob
• UICondSlider
• UICondSwitch
  etc etc.
  So there is about 10 conditional widget in Auburn codebase. Most of them define additional @ScriptProperty to control the appearance of the disabled widget.

All points towards a smallish Condition interpreter that can parse and evaluate an expression tree at given points in time (typically, when a listened parameter changes). For now the expression tree is implemented in Auburn codebase in a lame fixed way ( a set of && or || expressions, with 2 operators, and up to 12 operands).

Ideally we want:

• the 4 operators: < > >= <=,
• boolean and double expressions
• && and ||
• access to parameter
  The expression itself is evaluated when it's value may have changed.
  This evaluation will happen for many widgets, even inside audio thread as part of a host setParameter, and myst be quick!
• there is a pre-parse that registers / deregisters Parameter to be listened to.

This will allows the agreeable idioms:

• widget.enableIf(string expr); to control the .isDisabled state
• widget.showIf(string expr); to control visibility

Any widget has such a conditional extension. This will avoid the existence of:

Stage 1

• Add 2 owned CondLogic as a lazy extension of all UIElement. It's a set of || or && expression, suitable for most purposes but not very readable.
• All UIElement have a queryable .isEnabled and .isDisabled. By default true, unless the condition is created and return false.

Now the sub-class are easier to write, but there are still multiple subclasses. This is 80% of the value.

Stage 2

• Add an additional .enableIf call to UIElement that created the CondLogic and
• Implement widget.enableIf
• expression interpreter registers the listeners
• expression interpreter eval the condition
• The big issue is that because of our imperative styling, there is no way to not subclass in order to add the diffuseDisabled RGBA variables. Undoing that needs more declarative.
  * Perhaps find the semantic way to express al kind of disabled re-coloring.
• Should this be Wren? Should this be fe-d, a Forth-like?