Fixes #2482. Refactor Redraw - Non-virtual with the right set of virtual OnXXX methods.

[BDisp]

Fixes #2482 - Renaming Redraw to OnDraw and creating a method Draw with the entire draw process phases.

Draw call:

OnDrawFrames
OnDrawContent -> cancelable.
  OnDraw
OnRenderLineCanvas
OnDrawContentComplete

Others can also be cancelable.

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[tig]

Nice work!

Please see my comments. Let me know if I wasn't clear.

[BDisp]

@tig, @tznind please correct me if I'm wrong. If I want to prioritize an event to called before a overridden method is run, then is a danger invoking the event inside the virtual method. To avoid this the DrawContent must be invoked before and if it's canceled then the OnDrawContent won't be called . e.g. In this case bellow the DrawContent event will never be invoked. I think this is bad, right? The user must have a chance to use this event and return what he want.

			if (!OnDrawContent (Bounds)) {
				OnDraw ();
			}

		public virtual bool OnDrawContent (Rect contentArea)
		{
			var dev = new DrawEventArgs (contentArea);
			DrawContent?.Invoke (this, dev);

			return dev.Cancel;
		}

		public override bool OnDrawContent (Rect contentArea)
		{
			return true;
		}

I think this should be:

			var dev = new DrawEventArgs (contentArea);
			DrawContent?.Invoke (this, dev);
			if (!dev.Cancel) {
				OnDrawContent (Bounds);
			}

This way the DrawContent event is invoked and if it's canceled then the OnDrawContent method will not be called. If not canceled the OnDrawContent will be called. The OnDraw method isn't needed really.

[tig]

The OnDraw method isn't needed really.

I think you are spot on.

[tig]

@BDisp see merge conflicts.

[BDisp]

Due the ScreenToView fix the mouse grabbing on the Clipping scenario doesn't jumping anymore. The ScreenToBounds was removed because it doesn't used and thus is unnecessary.

[tig]

Really great work!