Trying Ada Bindings for X11

Posted on Tue 01 September 2015 in misc • View Comments

Ada bindings for X11 were written Intermentics company and sponsored by Ada Joint Program Office (AJPO).

While intemetics has long been gone (looks like the it's domain is owned by L3 now), and AJPO was closed in 1998, the bindings are still around.

The "latest" version can be downloaded from this page on adapower web site (the download link is at the bottom named x11ada)

I was surprised how smooth was the process of building and running a demo program. The following tutorial will walk through this process.

Setup

The tools I used for this tutorial are gnat 4.9.3 and gprbuild 2014.
Create a directory for your project. I called it "ada11_testing".
Download "x11ada_v1.30.tar.gz" from the link provided above. Inside you will find "ada" directory. Copy this whole directory to "ada11_testing".
Create a directory called "obj" inside "ada11_testing".

Project File

Create "test.gpr" file with the following contents:

project test is
  for main use ("test");

  for Source_Dirs use ("./**");

  for Object_Dir use "obj";

  for Exec_Dir use ".";

  package Linker is
     for Default_Switches("Ada") use ("-lX11");
  end Linker;

  package Compiler is
     for Default_Switches("Ada") use ("-gnateE", "-gnat2012"); 
  end Compiler;

  for Languages use ("Ada", "C");

end test;

Code

Being thin bindings, every C function of X11 library has an equivalent Ada function. Therefore example programs, documentation and tutorials that are aimed at C are suitable for Ada programmers as well.

I used example program from the following article of Linux Magazine.

with Interfaces.C;
with X;
with X.Xlib;

procedure Test is

   use type Interfaces.C.Int;
   use type Interfaces.C.Unsigned;
   use type X.Xlib.XDisplay_access;

   Cant_Open_Display_Error: exception;

   Display          : X.Xlib.XDisplay_access;
   Screen_Num       : Interfaces.C.Int;
   Win              : X.Window;
   Graphics_Context : X.Xlib.GC;
   Report           : aliased X.Xlib.XEvent;

begin

   Display := X.Xlib.XOpenDisplay( null );

   if Display = null  then
      raise Cant_Open_Display_Error;
   end if;

   Screen_num     := X.Xlib.DefaultScreen(Display);

   Win := X.Xlib.XCreateSimpleWindow
     (Display      => Display, 
      Parent       => X.Xlib.RootWindow(Display, Screen_Num), 
      XX           => 50, 
      Y            => 50, 
      Width        => 200, 
      Height       => 200, 
      Border_Width => 0, 
      Border       => X.Xlib.BlackPixel(Display, Screen_Num), 
      Background   => X.Xlib.WhitePixel(Display, Screen_Num));

   X.Xlib.XMapWindow(display, Win);

   X.Xlib.XSelectInput(Display, Win, X.StructureNotifyMask);

   loop
      X.Xlib.XNextEvent(Display, Report'access);

      exit when Report.Event_Type = X.MapNotify;
   end loop;

   Graphics_Context := X.Xlib.XDefaultGC(Display, Screen_Num);

   X.Xlib.XSetForeground(Display, Graphics_Context, X.Xlib.BlackPixel(Display, Screen_Num));

   X.Xlib.XDrawLine(Display, X.Drawable(Win), Graphics_Context, 10, 10, 190, 190);
   X.Xlib.XDrawLine(Display, X.Drawable(Win), Graphics_Context, 10, 190, 190, 10);

   X.Xlib.XSelectInput
     (Display, 
      Win, 
      Interfaces.C.Long( Interfaces.C.Unsigned( X.ButtonPressMask) or X.ButtonReleaseMask)
     );

   loop
      X.Xlib.XNextEvent(Display, Report'access);

      exit when Report.Event_Type = X.ButtonRelease;
   end loop;

   X.Xlib.XDestroyWindow(Display, Win);
   X.Xlib.XCloseDisplay(Display);

end Test;

Building with gprbuild:

gprbuild -P test.gpr

And that is all it takes to use 20 years old software package!

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Setup

Project File

Code

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