I am working on a Blasteroids clone in Allegro 5 (Win32, MSVC), courtesy of Head First C's last C Lab Project.
So far I've gotten to the point of successfully drawing the spaceship on the display, and I can move it around as well with transformations.
However, when I wanted to add an FPS display in the top right corner, I've hit a roadblock. Apparently, when using al_draw_textf() to display the current FPS, it uses the already set transformations from the spaceship. So when I move the ship, the FPS display moves with it.
I am using separate functions to move the spaceship and to draw the FPS, and they are in different files as well (but the same thread).
I'm guessing this has to do with bitmaps, and everything that I draw on the screen and want to have behaving independently from other objects has to be drawn to their respective bitmaps. (Please correct me if I'm wrong.)
I've gone through the several example programs bundled with Allegro but couldn't find a clean-cut solution as the code in those included extra noise/features that made it difficult to extract the only information that I need. Also learned about hardware and software rendering, and now got confused on which one to use (to be honest I have no idea which one I'm using right now either).
Now unfortunately I don't know too much about bitmaps, hardware/software rendering, etc. to solve this myself, so I ask for your help.
Drawing from spaceship.c:
#SelectExpand
1void draw_spaceship
(Spaceship
*ship
)
2{
3 ALLEGRO_TRANSFORM transform
;
4 al_identity_transform(&transform
);
5 al_rotate_transform(&transform, ship->heading
);
6 al_translate_transform(&transform, ship->sx, ship->sy
);
7 al_use_transform(&transform
);
8 al_draw_line(-8,
9,
0,
-11, ship->color,
3.
0f);
9 al_draw_line(0,
-11,
8,
9, ship->color,
3.
0f);
10 al_draw_line(-6,
4,
-1,
4, ship->color,
3.
0f);
11 al_draw_line(6,
4,
1,
4, ship->color,
3.
0f);
12}
Relevant parts of main.c:
#SelectExpand
1static ALLEGRO_DISPLAY *display
= NULL
;
2static ALLEGRO_EVENT_QUEUE *event_queue
= NULL
;
3static ALLEGRO_TIMER *timer
= NULL
;
4static ALLEGRO_BITMAP *dbuf
= NULL
;
5static Spaceship
*theShip
= NULL
;
6static ALLEGRO_FONT *font = NULL
;
7
8const float FPS
= 60;
9const int screenWidth
= 640;
10const int screenHeight
= 480;
11
12void init_game
(void)
13{
14 if(!al_init())
15 abort_game
("Failed to initialize allegro");
16
17 if(!al_install_keyboard())
18 abort_game
("Failed to install keyboard");
19
20 timer
= al_create_timer(1.
0 / FPS
);
21 if(!timer
)
22 abort_game
("Failed to create timer");
23
24 al_set_new_display_flags(ALLEGRO_WINDOWED
);
25 display
= al_create_display(screenWidth, screenHeight
);
26 if (!display
)
27 abort_game
("Failed to create display");
28
29 event_queue
= al_create_event_queue();
30 if(!event_queue
)
31 abort_game
("Failed to create event queue");
32
33 al_init_font_addon();
34
35 font = al_create_builtin_font
();
36 if (!font)
37 abort_game
("Failed to initialize builtin font");
38
39 al_register_event_source(event_queue,
al_get_display_event_source(display
));
40 al_register_event_source(event_queue,
al_get_timer_event_source(timer
));
41 al_register_event_source(event_queue,
al_get_keyboard_event_source());
42}
43
44void drawFPS
(double *old_time
)
45{
46 double new_time
= al_get_time();
47 double delta
= new_time
- *old_time
;
48 double fps
= (1 / (delta
* 1000)) * 1000;
49 al_draw_textf(font,
al_map_rgb(255,
255,
255),
0,
0, ALLEGRO_ALIGN_RIGHT,
"FPS: %d",
(int) fps
);
50 *old_time
= new_time
;
51}
52
53void update_graphics
(double *old_time
)
54{
55 // full redraw
56 al_clear_to_color(al_map_rgba_f(0,
0,
0,
0));
57 draw_spaceship
(theShip
);
58 // draw bullets
59 // draw asteroids
60 // draw GUI
61 drawFPS
(old_time
);
62 al_flip_display();
63}
64
65void init_bitmap
(void)
66{
67 if (!al_init_primitives_addon())
68 abort_game
("Failed to initialize the primitives addon");
69
70 dbuf
= al_create_bitmap(screenWidth, screenHeight
);
71 if (!dbuf
)
72 abort_game
("Failed to create bitmap");
73
74 al_set_target_bitmap(dbuf
);
75 al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_ZERO
);
76 al_draw_bitmap(dbuf,
0.
0,
0.
0,
0);
77 al_set_target_backbuffer(display
);
78}
79
80void game_loop
(void)
81{
82 bool redraw
= true;
83 bool isRunning
= true;
84
85 init_bitmap
();
86 al_start_timer(timer
);
87 theShip
= init_spaceship
();
88
89 // initial ship position
90 theShip->sx
= screenWidth
/ 2;
91 theShip->sy
= screenHeight
/ 2;
92
93 double old_time
= al_get_time();
94
95 /* start game loop */
96 while (isRunning
) {
97 ALLEGRO_EVENT event
;
98
99 al_wait_for_event(event_queue,
&event
);
100
101 if (event.type
== ALLEGRO_EVENT_KEY_DOWN
)
102 // input handling
103
104 else if (event.type
== ALLEGRO_EVENT_KEY_UP
)
105 // input handling
106
107 else if (event.type
== ALLEGRO_EVENT_TIMER
) {
108 redraw
= true;
109 // acting on input
110 }
111
112 else if (event.type
== ALLEGRO_EVENT_DISPLAY_CLOSE
)
113 isRunning
= false;
114
115 if (redraw
&& al_is_event_queue_empty(event_queue
)) {
116 redraw
= false;
117 update_graphics
(&old_time
);
118 }
119 }
120}
Any help would be greatly appreciated! 
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