The New Event-Based User Input System - TODO and bug-fixes

[mitchmindtree]

NOTE: Issue closed in favour of tracking progress at #703

This is a follow up of changes that are yet to be made following the implementation of conrod's new event-based user input system in #684 as discussed in #670.

Widgets that still need to be changed over to the new system:

• Button
• DropDownList
• EnvelopeEditor
• NumberDialer
• Slider
• Tabs (maybe?)
• TextBox
• TitleBar
• Toggle
• XYPad
• CircularButton (from custom_widget.rs example)

Other related todo:

• Review the Widget::drag_area method and related types and see if these can be removed in favour of using the new Drag events.
• Fix bug where widgets still receive Clicked events when covered by another widget (should be using Graph::pick_widget method).

[mitchmindtree]

@psFried I'm currently working away on the above and I noticed that we're creating drag events upon raw release events - I'm thinking of refactoring this to only generate drag events on raw move events as this feels a little more intuitive to me, but I'm curious to hear what your thoughts are on this first?

[mitchmindtree]

Ahh, I just noticed the in_progress field in the MouseDrag struct.

How about rather than combining state into the one MouseDrag event, we add DragStart and DragEnd events?

Also, I'm thinking of changing MouseDrag -> Drag and MouseClick -> Click, thoughts?

[mitchmindtree]

Going to close this issue in favour of tracking progress at #703