Is any difference, problems of porting 32-bit app to 64-bit?

[Cyrax]

It's by design. Under 64-bit Windows 64-bit programs goes under "Program Files" and 32-bit ones under "Program Files (x86)". Why do you need it to be compatible, anyway?

[Cyrax]

It seems to me already to be 'plug and play' unless you have some specific code that requires to do unique stuff. 64-bit programs does 64-bit stuff (can't call 32-bit stuff and vice versa) and 32-bit does 32-bit stuff.

[JuhaManninen]

I need all kind of mouse / keyboard / window messages.
For example following simple Delphi code is quite impossible. It captures (and eats) all right mouse clicks. No matter what component is under mouse.
[...]

True, it is not currently possible.
TOnUserInputEvent in Application lets you see and react to all mouse events. Unfortunately it does not let you "eat" or filter out the events.

Code: [Select]

procedure TForm1.FormCreate(Sender: TObject);
begin
  Application.AddOnUserInputHandler(@UserInputHandler);
end;

procedure TForm1.UserInputHandler(Sender: TObject; Msg: Cardinal);
begin
  ...
end;

There are other Application.AddOn... methods for other events, too.

It should be possible to extend OnUserInputEvent + handler to take a var param which you can change.
If you want to dive into LCL events and create a patch for such feature, I think it can be applied.
How much work or side-effects it causes, I have no idea.