Graeme Geldenhuys schrieb:
On a side note: I still have no clue how Qt managed to
make a smooth transition from "one handle per widget" to "single
handle per form" design.
Where do you see problems?
The OS has to track some global notification "targets", for e.g.
keyboard input or mouse capture. These targets are processes (or
threads) in the first place. With no such global target (e.g. on an
uncaptured mouse click) the screen/window manager can determine the
target process from the information, stored with every window. That's
why forms/windows always have a handle, assigned and used by the window
manager of a platform.
The determination of a closer target (e.g. control) is up to the
application or library, that manages the layout of a window. Every
application or library can freely define their own "handles" for every
possible notification target, as appropriate to dispatch incoming
notifications. The "natural" handle of every such target is the address
of the data structure, that describes the target. The LCL can use the
addresses of TComponent objects for its handles, while a widgetset can
use the addresses of its equivalent data objects.
Handles in general can be seen as pointers to data structures, or as
indices into according pointer tables, that make sense only to the owner
of those structures, within its own address space. E.g. GDI handles look
much like indices into some (sparse) pointer array, consisting of areas
for system wide objects (fonts...), and application or device context
specific objects.
DoDi
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