NotesOnModelViewControl

1) The Model: Buffer

The Buffer is the in-memory representation of a LyX file format. The 
Buffer does not (should not) have any information on what part of it is 
represented on screen. There is one unique Buffer per opened LyX file.

2) The Controller: BufferView/Painter

The BufferView is a tool used by the view that translates a part of the 
Buffer contents into drawing routines. The BufferView asks each inset of 
the Buffer to draw itself onto the screen using the Painter.
There is only Buffer loaded per BufferView. While there is the 
possibility to switch Buffer inside the BufferView, the goal is to 
instantiate a new BufferView on each Buffer switch.

The Painter is just a virtual interface to formalize each kind of 
drawing routines (text, line, rectangle, etc).

The BufferView also contains a Cursor which may or may not be visible on 
screen. The cursor is really just a bookmark to remember where the next 
Buffer insertion/deletion is going to take place.

3) The View: WorkArea (and it's qt4 specialisation GuiWorkArea)

This contains the real screen area where the drawing is done by the 
Painter. One WorkArea holds one unique BufferView. While it could be 
possible that multiple WorkArea share one BufferView, this is not 
possible right now.
The WorkArea also provide a scrollbar which position is translated into 
scrolling command to the inner BufferView.

The WorkArea use the BufferView to translate each keyboard or mouse 
events into terms that the Buffer can understand:
- insert/delete char
- select char
- etc.

4) The Window: LyXView (and its qt4 specialisation GuiView)

This is a full window containing a menubar, toolbars, a tabbar and a 
WorkArea. One LyXView could in theory contain multiple WorkArea (ex: 
with split window) but this number is limited to one only for now. In 
any case, there would be only one WorkArea that gets the focus at a time.

Now, concerning the TabBar versus TabWidget issue. Right now, there is 
only one WorkArea and the TabBar just used to tell the BufferView inside 
the WorkArea to switch to this another Buffer.
With a TabWidget, each Tab would own its own WorkArea. Clicking on a tab 
would switch a WorkArea instead of a Buffer.