How to make a phantom window in Delphi?

Question

Delphi

How to make a window in Delphi, but so that the cursor (i.e. click) passes "through it", as, for example, in the volume indicator on laptops?

Answer 1

1. Turn on the AlphaBlend property. Even if you want an opaque window, turn it on anyway.
2. Redefine two functions.

procedure TfmMain.CreateParams(var Param : TCreateParams);  // override
begin
  inherited;
  Param.ExStyle := Param.ExStyle or WS_EX_TRANSPARENT;
end;

procedure TfmMain.WmNcHitTest(var Msg : TWMNCHitTest); // message WM_NCHITTEST;
begin
  Msg.Result := HTTRANSPARENT;
end;