First, use
<code>
and
</code>
. 
In your first example, that is Allegro 5 code. In the bottom example with the set_gfx_mode(), that is older Allegro 4 code that you're seeing.
You are right though, if you wish to support full screen you will need to add in black bars or pick a resolution like 800x600 and just do window mode.
I had this same problem when Matthew Leverton helped me with this function which will do what you want. It basically uses ALLEGRO_TRANSFORM to fit the resolution you wish to the user's desktop resolution and stretches it up to fit rather than setting a new resolution.
This is a copy and paste of the function from my own game... feel free to use it.
Just pass this function the desktop resolution and the buffer width and height of your screen to be scaled up...
a5_scale_screen.c
#SelectExpand
1// Scale Screen:
2// Sets up transforms in order to fit any resolution
3// onto an ALLEGRO_FULLSCREEN_WINDOW.
4//
5// (Special thanks to Matthew Leverton for help with this!)
6
7#include "a5_scale_screen.h"
8
9
10
11// Use to get mouse position on scaled screen
12float scale_x
= 1;
13float scale_y
= 1;
14int offset_x
= 0;
15int offset_y
= 0;
16
17
18
19// usage: a5_scale_screen(BUFFER_WIDTH, BUFFER_HEIGHT, display_width, display_height);
20void a5_scale_screen
(int bw,
int bh,
int dw,
int dh
)
21{
22 ALLEGRO_TRANSFORM t
;
23
24 // Calculate the horizontal and vertial aspect ratios
25 const float HAR
= dw
/ (float)bw
;
26 const float VAR
= dh
/ (float)bh
;
27
28 // The aspect ratio, x-offset and y-offset (in pixels)
29 float ar, ox, oy
;
30
31 if(bw
== dw
&& bh
== dh
) {
32 // 1:1, just reset everything
33 al_identity_transform(&t
);
34 al_use_transform(&t
);
35 al_set_clipping_rectangle(0,
0, bw, bh
);
36 scale_x
= 1;
37 scale_y
= 1;
38 offset_x
= 0;
39 offset_y
= 0;
40 al_clear_to_color(al_map_rgb(0,
0,
0));
41 al_flip_display();
42 }
43 else {
44 // Choose the smaller aspect ratio
45 if(HAR
< VAR
) {
46 // horizontal bars on the top and bottom
47 ar
= HAR
;
48 ox
= 0;
49 oy
= (dh
- (ar
* bh
)) / 2.
0;
50 }
51 else {
52 // vertical bars on the left and right
53 ar
= VAR
;
54 ox
= (dw
- (ar
* bw
)) / 2.
0;
55 oy
= 0;
56 }
57
58 // set the global scale/offset so the mouse coords can be inverted
59 // use the following code to get the proper mouse position
60 // mouse_x = (event.mouse.x - offset_x) / scale_x;
61 // mouse_y = (event.mouse.y - offset_y) / scale_y;
62 scale_x
= ar
;
63 scale_y
= ar
;
64 offset_x
= ox
;
65 offset_y
= oy
;
66
67 // set up the transformation to scale and translate
68 al_build_transform(&t, ox, oy, ar, ar,
0);
69 al_use_transform(&t
);
70
71 // clear out the screen before setting the clipping
72 al_set_clipping_rectangle(0,
0, dw, dh
);
73 al_clear_to_color(al_map_rgb(0,
0,
0));
74 al_flip_display();
75
76 // make sure nothing is drawn into the black bars
77 al_set_clipping_rectangle(ox, oy, ar
* bw, ar
* bh
);
78 }
79}
and the header file I use...
a5_scale_screen.h
#ifndef _a5_scale_screen_h_
#define _a5_scale_screen_h_
#include <allegro5/allegro.h>
extern float scale_x;
extern float scale_y;
extern int offset_x;
extern int offset_y;
// usage: a5_scale_screen(BUFFER_WIDTH, BUFFER_HEIGHT, display_width, display_height);
void a5_scale_screen(int bw, int bh, int dw, int dh);
#endif
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