I'm getting some interesting behavior using Allegro 5 with GLTools. I'm learning openGL in my computer graphics class and for a class project I'm creating a quick shooter demo. I've used Allegro 4 before, and since Allegro 5 supports openGL, I've decided to reduce some of the complexity and use Allegro 5. I've copied some code from the OpenGL Superbible 5ed, and want to use a shader to create a moving star background. The book uses GLTools to simplify things and I've got all the GLTools stuff to work, however I cant seem to draw both my sprites and the star background. I can either draw the star background, or I can draw the sprites. When I try to draw both the stars and the sprites the stars get replaced by my sprites in a weird combination. Could someone look at my code and let me know what needs to be fixed? Thanks.

I'm also having a hard time keeping track of the OpenGL state looking just at the code snippet. I'd try getting rid of the al_set_target_bitmap() and al_set_current_opengl_context() calls unless you know exactly why you need them and what they do.

glBindTexture tells OpenGL what texture to use for all the OpenGL calls following it, until another glBindTexture is called. i.e.

glBindTexture(someTexture1);
...
a bunch of OpenGL calls
(all of this will be drawn using someTexture1)
...
glBindTexture(someTexture2);
...
more OpenGL calls
(all of this will be drawn using someTexture2)
...

Now, al_draw_bitmap, internally, must call glBindTexture on the bitmap being drawn, so that it can ... well, draw it! So ...

al_draw_bitmap(some_awesome_image);
...
a bunch of OpenGL calls
(all of these will be drawn using some_awesome_image)
...
glBindTexture(someTexture2);
...
more OpenGL calls
(all of these will be drawn using someTexture2)

So, as you can see, by calling al_draw_bitmap, you've changed what texture is currently being used by OpenGL.

You'll have to assist me in deciphering the specifics of your code. Is master->update_members the call that draws your sprites? or is it al_draw_bitmap(buffer, 0, 0, ALLEGRO_VIDEO_BITMAP)

Would you mind showing the code for update_members? Do you call:

al_set_target_bitmap(buffer);
At the top of update_members?

If you don't, that's the problem. Or do this, if master doesn't have buffer in its scope:

al_set_target_bitmap(buffer);
master->update_members(clock(), total_frames, scroll);

Also, I don't think ALLEGRO_VIDEO_BITMAP is a valid flag for al_draw_bitmap. It should probably just be:

al_draw_bitmap(buffer, 0, 0, 0);

Well if setup_background is indeed causing the trouble, try commenting out pieces of setup_background one by one to narrow it down. I, too, can't see anything in there that would mess up the OpenGL state.

And just to double check, you commented out all of the starfield rendering related code, except for setup_background, and it displayed a black screen? But then also commenting out setup_background fixed it?

Okay, this is going to be fun!

Try doing this before drawing your sprites:

glDisableVertexAttribArray(GLT_ATTRIBUTE_VERTEX);
glDisableVertexAttribArray(GLT_ATTRIBUTE_COLOR);
glDisableVertexAttribArray(GLT_ATTRIBUTE_NORMAL);
glDisableVertexAttribArray(GLT_ATTRIBUTE_TEXTURE0);
glDisableVertexAttribArray(GLT_ATTRIBUTE_TEXTURE1);
glUseProgram(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);

If you call Color4fv, or Vertex3fv on a GLBatch, it will muck with OpenGL's state. And obviously glUseProgram will tell OpenGL to use the shading program, even while calling al_draw_bitmap Hopefully the above will undo everything and make Allegro happy.

Thank goodness! I'm glad you got it working And thank you for posting the working code, most people forget to post their solutions