About shaders and ALLEGRO_BITMAPS

no-reply@allegro.cc (paulwayne) — Wed, 07 Dec 2016 02:31:29 +0000

I want to use shaders to create a 2d shadowing effect like this

I have a simple shader that i can apply to the current display, and that works fine. Like this:

#SelectExpand
 1al_set_target_backbuffer(display);
 2al_use_shader(shader);
 3.. draw
 4al_use_shader(NULL);
 5al_flip_display();

But when i try to use the shaders with a bitmap i cant make this to work.
Basically i want to apply the shader to a bitmap like this:

#SelectExpand
  1//draw things to bitmap
  2al_set_target_bitmap(bmp);
  3al_use_shader(shader);
  4.. draw
  5al_use_shader(NULL);
  6
  7//now display it
  8al_set_target_backbuffer(display);
  9al_clear_to_color(al_map_rgb(0, 0, 0));
 10al_draw_bitmap(bmp, 0, 0, 0);

Maybe is something im missing since im new to allegro, any idea?
Im using the last source version of allegro.

no-reply@allegro.cc (SiegeLord) — Wed, 07 Dec 2016 22:26:47 +0000

It should work, I just tried it on Linux and it seemed fine. What platform are you on?

no-reply@allegro.cc (paulwayne) — Thu, 08 Dec 2016 00:46:03 +0000

Im on Windows 7 32 bits, Visual Studio 2013, and last Allegro version.

no-reply@allegro.cc (SiegeLord) — Thu, 08 Dec 2016 12:02:58 +0000

Interesting. I tried it on Windows myself, and it seemed to work ok.

Try adding this line before al_init() to enable logging (it'll generate an allegro.log file in your working directory when you run the program):

al_set_config_value(al_get_system_config(), "trace", "level", "debug");

It'll be useful to look at that log.

Additionally, try doing this before you create the display to force OpenGL mode (by default, Allegro uses Direct3D on Windows):

al_set_new_display_flags(ALLEGRO_PROGRAMMABLE_PIPELINE | ALLEGRO_OPENGL);

Lastly, it'll be helpful if you produced a tiny program that reproduced your issue, so we can verify it's not something wrong in your code.

no-reply@allegro.cc (paulwayne) — Fri, 09 Dec 2016 08:56:24 +0000

I finally got this to work. There was a problem with the shaders i was using. /facepalm