I'm trying to do the following:
draw some stuff to the backbuffer
render the backbuffer to bitmap_a
clear the backbuffer, and draw some different stuff to the backbuffer
render the backbuffer to bitmap_b
clear the backbuffer
draw bitmap_a and bitmap_b to the backbuffer
flip
I'm able to do this just fine, but when 1) multi-sampling is enabled and 2) it's in directx, somehow bitmap_a clears out (becomes transparent or something.) I'm using 5.0.5.
Here's my example program:
#SelectExpand
1#include <allegro5/allegro.h>
2#include <allegro5/allegro_color.h>
3#include <allegro5/allegro_primitives.h>
4#include <allegro5/allegro_image.h>
5
6
7
8void main
()
9{
10 int screen_w
= 320;
11 int screen_h
= 240;
12 float shape_size
= screen_w
/4;
13 bool save_renders
= true;
14
15 al_init();
16 al_init_primitives_addon();
17 al_init_image_addon();
18
19
20 al_set_new_display_option(ALLEGRO_SAMPLE_BUFFERS,
2, ALLEGRO_SUGGEST
); // works only in opengl
21 al_set_new_display_option(ALLEGRO_SAMPLES,
4, ALLEGRO_SUGGEST
); // works only in opengl
22 //al_set_new_display_flags(ALLEGRO_OPENGL);
23
24
25 // create the display and 2 surfaces
26 ALLEGRO_DISPLAY *display
= al_create_display(screen_w, screen_h
);
27 ALLEGRO_BITMAP *surface_a
= al_create_bitmap(screen_w, screen_h
);
28 ALLEGRO_BITMAP *surface_b
= al_create_bitmap(screen_w, screen_h
);
29
30
31 // draw the content of surface_a
32 al_clear_to_color(al_color_name("orange"));
33 al_draw_filled_circle(screen_w
/2, screen_h
/2, shape_size,
al_map_rgba_f(0.
2,
0.
2,
0.
2,
0.
2));
34
35 al_set_target_bitmap(surface_a
);
36 al_draw_bitmap(al_get_backbuffer(display
),
0,
0, NULL
);
37
38 if (save_renders
) al_save_bitmap("surface_a_first.png", surface_a
);
39 if (save_renders
) al_save_bitmap("surface_b_first.png", surface_b
);
40
41
42 // reset the surface (oops! forgot to put this in)
44
45
46
47 // draw the content of surface_b
48 al_clear_to_color(al_color_name("dodgerblue"));
49 al_draw_filled_rectangle(screen_w
/2-shape_size, screen_h
/2-shape_size,
50 screen_w
/2+shape_size, screen_h
/2+shape_size,
al_map_rgba_f(0.
2,
0.
2,
0.
2,
0.
2));
51
52 al_set_target_bitmap(surface_b
);
53 al_draw_bitmap(al_get_backbuffer(display
),
0,
0, NULL
);
54
55 if (save_renders
) al_save_bitmap("surface_a_second.png", surface_a
);
56 if (save_renders
) al_save_bitmap("surface_b_second.png", surface_b
);
57
58
59
60 // draw surface_a and surface_b blended together
61 al_set_target_bitmap(al_get_backbuffer(display
));
62
63 al_draw_bitmap(surface_a,
0,
0, NULL
);
64 al_draw_tinted_bitmap(surface_b,
al_map_rgba_f(0.
5,
0.
5,
0.
5,
0.
5),
0,
0, NULL
);
65
66
67 if (save_renders
) al_save_bitmap("surface_a_final.png", surface_a
);
68 if (save_renders
) al_save_bitmap("surface_b_final.png", surface_b
);
69
70
71 // flip the dip!
72 al_flip_display();
73
74
75 al_rest(5);
76
77 return;
78}
Here's what surface_a should look like:
{"name":"605444","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/6\/2\/62d9ac52c30ecd7a0aa64a677eed8c90.png","w":320,"h":240,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/6\/2\/62d9ac52c30ecd7a0aa64a677eed8c90"}
and surface_b:
{"name":"605445","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/f\/6\/f6c9dcad47059e363812e9693c024084.png","w":320,"h":240,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/f\/6\/f6c9dcad47059e363812e9693c024084"}
and the expected result:
{"name":"605443","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/c\/4\/c45fea4057d9b8317ed36c77f9f78b57.png","w":402,"h":324,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/c\/4\/c45fea4057d9b8317ed36c77f9f78b57"}
After looking a little deeper, it seems that there's some other strange things going on. When the <code>save_renders=true</code>, configurations of OpenGL/DirectX/multi-sampling produce different resulting saved bitmaps. When it looks like it's working with OpenGL, it actually just appears to be working while the stuff on <code>bitmap_a</code> and <code>bitmap_b</code> are getting swapped in the process. ???
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