OpenGL

al_get_opengl_extension_list

ALLEGRO_OGL_EXT_LIST *al_get_opengl_extension_list(void)

Returns the list of OpenGL extensions supported by Allegro, for the current display.

Allegro will keep information about all extensions it knows about in a structure returned by al_get_opengl_extension_list.

For example:

if (al_get_opengl_extension_list()->ALLEGRO_GL_ARB_multitexture) {
    use it
}

The extension will be set to true if available for the current display and false otherwise. This means to use the definitions and functions from an OpenGL extension, all you need to do is to check for it as above at run time, after acquiring the OpenGL display from Allegro.

Under Windows, this will also work with WGL extensions, and under Unix with GLX extensions.

In case you want to manually check for extensions and load function pointers yourself (say, in case the Allegro developers did not include it yet), you can use the al_is_opengl_extension_supported and al_get_opengl_proc_address functions instead.

al_get_opengl_proc_address

void *al_get_opengl_proc_address(AL_CONST char *name)

Helper to get the address of an OpenGL symbol

Example:

How to get the function glMultiTexCoord3fARB that comes with ARB's Multitexture extension:

// define the type of the function
   ALLEGRO_DEFINE_PROC_TYPE(void, MULTI_TEX_FUNC,
      (GLenum, GLfloat, GLfloat, GLfloat));
// declare the function pointer
   MULTI_TEX_FUNC glMultiTexCoord3fARB;
// get the address of the function
   glMultiTexCoord3fARB = (MULTI_TEX_FUNC) al_get_opengl_proc_address(
      "glMultiTexCoord3fARB");

If glMultiTexCoord3fARB is not NULL then it can be used as if it has been defined in the OpenGL core library. Note that the use of the ALLEGRO_DEFINE_PROC_TYPE macro is mandatory if you want your program to be portable.

Parameters:

name - The name of the symbol you want to link to.

Return value:

A pointer to the symbol if available or NULL otherwise.

al_get_opengl_texture

GLuint al_get_opengl_texture(ALLEGRO_BITMAP *bitmap)

Returns the OpenGL texture id internally used by the given bitmap if it uses one, else 0.

Example:

bitmap = al_load_bitmap("my_texture.png");
texture = al_get_opengl_texture(bitmap);
if (texture != 0)
    glBindTexture(GL_TEXTURE_2D, texture);

al_get_opengl_texture_size

void al_get_opengl_texture_size(ALLEGRO_BITMAP *bitmap, int *w, int *h)

Retrieves the size of the texture used for the bitmap. This can be different from the bitmap size if OpenGL only supports power-of-two sizes or if it is a sub-bitmap.

al_get_opengl_texture_position

void al_get_opengl_texture_position(ALLEGRO_BITMAP *bitmap, int *u, int *v)

Returns the u/v coordinates for the top/left corner of the bitmap within the used texture, in pixels.

al_get_opengl_fbo

GLuint al_get_opengl_fbo(ALLEGRO_BITMAP *bitmap)

Returns the OpenGL FBO id internally used by the given bitmap if it uses one, else 0. An FBO is created for a bitmap when you call al_set_target_bitmap for it.

al_remove_opengl_fbo

void al_remove_opengl_fbo(ALLEGRO_BITMAP *bitmap)

If the bitmap has an OpenGL FBO created for it (see al_set_target_bitmap), it is freed. It also is freed automatically when the bitmap is destroyed.

al_is_opengl_extension_supported

int al_is_opengl_extension_supported(AL_CONST char *extension)

This function is a helper to determine whether an OpenGL extension is available on the current display or not.

Example:

int packedpixels = al_is_opengl_extension_supported("GL_EXT_packed_pixels");

If packedpixels is TRUE then you can safely use the constants related to the packed pixels extension.

Parameters:

extension - The name of the extension that is needed

Return value:

TRUE if the extension is available FALSE otherwise.

al_get_opengl_version

float al_get_opengl_version(void)

Returns the OpenGL version number of the client (the computer the program is running on), for the current DISPLAY. "1.0" is returned as 1.0, "1.2.1" is returned as 1.21, and "1.2.2" as 1.22, etc.

A valid OpenGL context must exist for this function to work, which means you may not call it before al_create_display().

OpenGL configuration

You can disable the detection of any OpenGL extension by Allegro with a section like this in allegro5.cfg:

[opengl_disabled_extensions]
GL_ARB_texture_non_power_of_two=0
GL_EXT_framebuffer_object=0

Any extension which appears in the section is treated as not available (it does not matter if you set it to 0 or any other value).