PROGRAM HelloWorld;
(* First Allegro program. *)

USES
  allegro5, al5font, al5image, al5primitives;



(* Helper to test intialization. *)
  PROCEDURE MustInit (aTest: BOOLEAN; aDescription: STRING);
  BEGIN
    IF NOT aTest THEN
    BEGIN
      WriteLn ('couldn''t initialize ', aDescription, '.');
      WriteLn ('Press [Enter] to close.');
      ReadLn;
      Halt (1)
    END
  END;



(* Helper to assign vertex. *)
  FUNCTION CreateVertex (CONST x, y: REAL; CONST Color: ALLEGRO_COLOR)
    : ALLEGRO_VERTEX; INLINE;
  BEGIN
    CreateVertex.x := x; CreateVertex.y := y; CreateVertex.z := 0;
    CreateVertex.u := 0; CreateVertex.v := 0;
    CreateVertex.color := Color
  END;

VAR
  Timer: ALLEGRO_TIMERptr;
  Queue: ALLEGRO_EVENT_QUEUEptr;
  Event: ALLEGRO_EVENT;
  Display: ALLEGRO_DISPLAYptr;
  Font: ALLEGRO_FONTptr;

  Redraw, EndProgram: BOOLEAN;

  Mysha: ALLEGRO_BITMAPptr;

  v: ARRAY [0..3] OF ALLEGRO_VERTEX;

BEGIN
{ Initialization. }
  MustInit (al_init, 'Allegro');
  MustInit (al_install_keyboard, 'keyboard');

  Timer := al_create_timer (1.0 / 30.0);
  MustInit (Assigned (Timer), 'timer');

{ Create display. }
  al_set_new_display_option (ALLEGRO_SAMPLE_BUFFERS, 1, ALLEGRO_SUGGEST);
  al_set_new_display_option (ALLEGRO_SAMPLES, 8, ALLEGRO_SUGGEST);
  al_set_new_bitmap_flags (ALLEGRO_MIN_LINEAR OR ALLEGRO_MAG_LINEAR);
  Display := al_create_display (640, 480);
  MustInit (Assigned (Display), 'display');

{ Init/load graphics. }
  Font := al_create_builtin_font;
  MustInit (Assigned (Font), 'font');

  MustInit (al_init_image_addon, 'image addon');

  Mysha := al_load_bitmap ('mysha.png');
  MustInit (Assigned (Mysha), 'mysha');

  MustInit (al_init_primitives_addon, 'primitives');

{ Create event queue. }
  Queue := al_create_event_queue;
  MustInit (Assigned (Queue), 'queue');

  al_register_event_source (Queue, al_get_keyboard_event_source);
  al_register_event_source (Queue, al_get_display_event_source(Display));
  al_register_event_source (Queue, al_get_timer_event_source (Timer));

{ Create "complex" graphic. }
  v[0] := CreateVertex (210, 320, al_map_rgb_f(1, 0, 0));
  v[1] := CreateVertex (330, 320, al_map_rgb_f(0, 1, 0));
  v[2] := CreateVertex (210, 420, al_map_rgb_f(0, 0, 1));
  v[3] := CreateVertex (330, 420, al_map_rgb_f(1, 1, 0));

{ Initialize loop stuff. }
  Redraw := TRUE;
  EndProgram := FALSE;

  al_start_timer (Timer);
{ Main loop. }
  REPEAT
    al_wait_for_event (Queue, @Event);

    CASE Event.ftype OF
    ALLEGRO_EVENT_TIMER:
    { Game logic goes here. }
      Redraw := TRUE;
    ALLEGRO_EVENT_KEY_DOWN, ALLEGRO_EVENT_DISPLAY_CLOSE:
    { Close the program. }
      EndProgram := TRUE;
    END;

  { If must redraw and there's nothing pending... }
    IF Redraw AND al_is_event_queue_empty (Queue) THEN
    BEGIN
      al_clear_to_color (al_map_rgb (0, 0, 0));
      al_draw_text (Font, al_map_rgb (255, 255, 255), 0, 0, 0, 'Hello world!');
      al_draw_bitmap (Mysha, 100, 100, 0);

      al_draw_filled_triangle (35, 350, 85, 375, 35, 400, al_map_rgb_f (0, 1, 0));
      al_draw_filled_rectangle (240, 260, 340, 340, al_map_rgba_f (0, 0, 0.5, 0.5));
      al_draw_circle (450, 370, 30, al_map_rgb_f (1, 0, 1), 2);
      al_draw_line (440, 110, 460, 210, al_map_rgb_f (1, 0, 0), 1);
      al_draw_line (500, 220, 570, 200, al_map_rgb_f (1, 1, 0), 1);

      al_draw_prim (v, Nil, 0, 4, ALLEGRO_PRIM_TRIANGLE_STRIP);
    { Drawing was done in a backbuffer. }
      al_flip_display;
    { Updated. }
      Redraw := FALSE
    END
  UNTIL EndProgram;
{ Release resources. }
  al_destroy_bitmap (mysha);
  al_destroy_font (Font);
  al_destroy_display (Display);
  al_destroy_timer (Timer);
  al_destroy_event_queue (Queue)
END.