23. Terminal: controlling the console

Applications generally provide user feedback either via full-fledge graphical interfaces, or via a simpler, console-based output.

The basic support for console-based output is provided directly via Ada.Text_IO. But more advanced features are highly system-dependent, and somewhat tricky to develop.

The package GNATCOLL.Terminal provide cross-platform support for manipulating colors in terminals, as well as a few basic cursor manipulation subprograms.

23.1. Colors

Most modern terminals support color output, generally with a limit set of colors. On Unix systems, these colors are set by using escape sequences in the output; on Windows systems, these are manipulated by calling functions on a file handle.

GNATCOLL will automatically try to guess whether its output is sent to a color enabled terminal. In general, this will be true when outputing to standard output or standard error, and false when outputing to files or to pipes. You can override this default value to force either color support or black-and-white support.

Here is an example:

with Ada.Text_IO;        use Ada.Text_IO;
with GNATCOLL.Terminal;  use GNATCOLL.Terminal;

procedure Test_Colors is
   Info : Terminal_Info;
begin
   Info.Init_For_Stdout (Auto);

   Info.Set_Color (Standard_Output, Blue, Yellow);
   Put_Line ("A blue on yellow line");

   Info.Set_Color (Standard_Output, Style => Reset_All);
   Put_Line ("Back to standard colors -- much better");
end Test_Colors;

23.2. Cursors

It is often useful for an application to display some progress indicator during long operations. GNATCOLL.Terminal provides a limit set of subprograms to do so, as in:

with Ada.Text_IO;        use Ada.Text_IO;
with GNATCOLL.Terminal;  use GNATCOLL.Terminal;

procedure Test_Colors is
   Info : Terminal_Info;
begin
   Info.Init_For_Stdout (Auto);
   for J in 1 .. 1_000 loop
      if J mod 10 = 0 then
         Put ("Processing file" & J'Img & " with long name");
      else
         Put ("Processing file" & J'Img);
      end if;
      delay 0.1;
      Info.Beginning_Of_Line;
      Info.Clear_To_End_Of_Line;
   end loop;
end Test_Colors;