Declaration:  GetLine(Var p1x: double; Var p1y: double; Var p2x: double; Var p2y: double; Hint: String): Integer;
Prompts the user to click 2 points on the active plan to define a line then returns the coordinates in p1 and p2.

Returns 1 if the function is successfull or 0 if the user cancels.

Source Code:

var
  x1, x2, y1, y2: double;

begin
  if GetLine(x1, y1, x2, y2, 'Click each end of a line.') = 1 then
    Showmessage('Draw line here')
  else
    Showmessage('Canceled');
end;