[Lazarus] Docking manager implementation

[Paul Ishenin]

Hans-Peter Diettrich wrote:

> The question is, how to proceed. Should I provide a new Lazarus unit, as 
> an alternative for LDockTree, or should I update LDockTree and Controls 
> and submit an patch? Be warned: my implementation changes fields, 
> methods and properties of TDockZone, and also parts of TDockTree, so 
> that other docking managers will have to be updated. That's why a new 
> unit might be a better introduction for this changed base classes.

Lets start with a new unit. Then we will see if we need our own 
LazDockTree or we will replace it with yours.

> Still missing is the anchoring, as done in TLazDockTree, and the 
> handling of messages and the display of the zone headers. It would be 
> nice to have a true TDockHeader component, derived from a 
> TCustomSplitter, so that only one additional component has to be managed 
> (anchored...), instead of separate zone header and splitter components. 
> Is this feasable?

Nice idea. Really dock header can be a splitter and a header at one 
moment. If we use 2 controls they will be anyway placed one by one.

> The header part and message processing can be taken from LDockTree, but 
> I'd suggest more changes to the anchoring of the docked components. IMO 
> the anchors are affected only by InsertControl and RemoveControl, not by 
> other changes like a resize of the docking site, so that the required 
> changes to the anchors could be reduced to just the insertion and 
> removal (docking and undocking) of a control.

ok

> For required size adjustments, after un/docking or a resize of the dock 
> site, multiple algorithms are applicable. In the simplest case the space 
> is distributed equally onto the docked controls. But the space also can 
> be distributed proportionally, according to the current or undocked size 
> of the controls. It might be a good idea to leave the choice to the 
> user, by means of an OnResize handler, or by a dedicated virtual method. 
> I'd like similar adjustments/selections for layout managers in general, 
> so that a coder can use the simple Delphi or the complicated Lazarus 
> anchors, or any other (Java like...) layout managers. Then a docking 
> manager can be reduced to just the handling of un/docking controls, 
> whereas the layout of the dock site could be delegated to an appropriate 
> layout manager.

Yes, options are possible. But I have no idea how Java or any others 
layout manager works. Maybe Mattias will help you here.

Best regards,
Paul Ishenin.