Set the position of a help window

Problem/Question/Abstract:

If you open a help file from your application, the help window always initializes at the same position. How do you change that, for instance to position a help window side by side with your form?

Answer:

You can use the Winhelp macro PositionWindow.

procedure TForm1.Button1Click(Sender: TObject);
var
  command: array[0..255] of Char;
begin
  command := 'PW(0, 0, 512, 512, 1, "main")';
  application.helpcommand(HELP_COMMAND, Longint(@command));
end;

What it does:

The code example above uses the HELP_COMMAND constant to execute a macro. The macro we use here is "PositionWindow" or - short - "PW". It defines the upper left corner (x1, y1) as (0,0) and the lower right corner (x2, y2) as (512,512).
The following parameter is the integer constant for "SW_SHOWNORMAL". Winhelp does not recognize the string "sw_shownormal" in the macro string. The last parameter is the name of the window.

One word about the coordinates:

The position and size of a help window always relates to a virtual screen size of 1024 x 1024 pixel, regardless of the screen resolution. If you set the size to (0, 0, 1024, 512), the help window would cover exactly the upper half of the screen.