Getting rid of MACHINE_CLICKABLE_ARTWORK system flag

[cuavas]

We all know the MACHINE_CLICKABLE_ARTWORK system flag is bad. Arguments against it include:

• The name doesn’t reflect what the flag does (causes the UI manager to display pointers for the system).
• There’s no such thing as a system that requires clickable artwork. You can use input assignments and/or scripting (plugins or auto-boot scripts) to control any of systems that have interactive artwork.
• Whether pointer display is useful or not depends on the layout view, not the system. For example an automatically-generated screen-only view will not benefit from pointer display while a front panel view with clickable switches will.
• There are systems with no internal layout views that benefit from pointer display where external artwork with clickable controls is available. The flag won’t be set for these systems, so they won’t have visible pointers.

Now that pointer event flow is in at least a bit better shape, I can look at getting rid of this flag.

After a bit of thought, my idea for the design is:

• Add a “show pointers” flag to layout views.
• Make the “show pointers” flag default to true if clickable items are found, or false otherwise.
• Allow the default to be overridden with an attribute on the <view> element.
• Allow layout scripts to change the “show pointers” flag on-the-fly.
• Have an inactivity timeout to hide mouse pointers (pen pointers don’t need it because they disappear when the pen leaves proximity, and touch pointers aren’t displayed at all).
• Allow the timeout to be disabled using an attribute on the <view> element or from layout scripts.

This should give reasonable default behaviour:

• No pointers displayed for views without clickable items.
• Pointers displayed for views with clickable items.
• Possible to disable inactivity timeout if you’re expecting to keep the pointer still waiting for something to happen but still want to be able to see where it is.
• Possible to override everything from within the layout file, so external artwork isn’t stuck with behaviour locked in place at compile time.

If anyone wants to poke holes in this, go ahead.