al_attach_shader_source(3)

NAME

al_attach_shader_source - Allegro 5 API

SYNOPSIS

    #include <allegro5/allegro.h>
    bool al_attach_shader_source(ALLEGRO_SHADER *shader, ALLEGRO_SHADER_TYPE type,
        const char *source)

DESCRIPTION

Attaches the shader’s source code to the shader object and compiles it. Passing NULL deletes the underlying (OpenGL or DirectX) shader. See also al_attach_shader_source_file(3) if you prefer to obtain your shader source from an external file.

If you do not use ALLEGRO_PROGRAMMABLE_PIPELINE Allegro’s graphics functions will not use any shader specific functions themselves. In case of a system with no fixed function pipeline (like OpenGL ES 2 or OpenGL 3 or 4) this means Allegro’s drawing functions cannot be used.

TODO: Is ALLEGRO_PROGRAMMABLE_PIPELINE set automatically in this case?

When ALLEGRO_PROGRAMMABLE_PIPELINE is used the following shader uniforms are provided by Allegro and can be accessed in your shaders:

al_projview_matrix
    matrix for Allegro’s orthographic projection multiplied by the al_use_transform(3) matrix. The type is mat4 in GLSL, and float4x4 in HLSL.

al_use_tex
    whether or not to use the bound texture. The type is bool in both GLSL and HLSL.

al_tex
    the texture if one is bound. The type is sampler2D in GLSL and texture in HLSL.

al_use_tex_matrix
    whether or not to use a texture matrix (used by the primitives addon). The type is bool in both GLSL and HLSL.

al_tex_matrix
    the texture matrix (used by the primitives addon). Your shader should multiply the texture coordinates by this matrix. The type is mat4 in GLSL, and float4x4 in HLSL.

With GLSL alpha testing is done in the shader and uses these additional uniforms:

al_alpha_test
    Whether to do any alpha testing. If false, the shader should render the pixel, otherwise it should interpret the values of al_alpha_func and al_alpha_test_val.

al_alpha_func
    The alpha testing function used. One of the ALLEGRO_RENDER_FUNCTION(3) values. The default is ALLEGRO_RENDER_ALWAYS which means all pixels (even completely transparent ones) are rendered. The type is int. See ALLEGRO_RENDER_STATE(3).

al_alpha_test_val
    If alpha testing is not ALLEGRO_RENDER_NEVER or ALLEGRO_RENDER_ALWAYS the alpha value to compare to for alpha testing. The type is float.

For GLSL shaders the vertex attributes are passed using the following variables:

al_pos
    vertex position attribute. Type is vec4.

al_texcoord
    vertex texture coordinate attribute. Type is vec2.

al_color
    vertex color attribute. Type is vec4.

al_user_attr_0
    The vertex attribute declared as ALLEGRO_PRIM_USER_ATTR

al_user_attr_1, ..., al_user_attr_9
    The vertex attribute declared as ALLEGRO_PRIM_USER_ATTR + X where X is an integer from 1 to 9

For HLSL shaders the vertex attributes are passed using the following semantics:

POSITION0
    vertex position attribute. Type is float4.

TEXCOORD0
    vertex texture coordinate attribute. Type is float2.

TEXCOORD1
    vertex color attribute. Type is float4.

Also, each shader variable has a corresponding macro name that can be used when defining the shaders using string literals. Don’t use these macros with the other shader functions as that will lead to undefined behavior.

•   ALLEGRO_SHADER_VAR_PROJVIEW_MATRIX for “al_projview_matrix”

•   ALLEGRO_SHADER_VAR_POS for “al_pos”

•   ALLEGRO_SHADER_VAR_COLOR for “al_color”

•   ALLEGRO_SHADER_VAR_TEXCOORD for “al_texcoord”

•   ALLEGRO_SHADER_VAR_USE_TEX for “al_use_tex”

•   ALLEGRO_SHADER_VAR_TEX for “al_tex”

•   ALLEGRO_SHADER_VAR_USE_TEX_MATRIX for “al_use_tex_matrix”

•   ALLEGRO_SHADER_VAR_TEX_MATRIX for “al_tex_matrix”

•   ALLEGRO_SHADER_VAR_ALPHA_FUNCTION for “al_alpha_func”

•   ALLEGRO_SHADER_VAR_ALPHA_TEST_VALUE for “al_alpha_test_val”

Examine the output of al_get_default_shader_source(3) for an example of how to use the above uniforms and attributes.

Returns true on success and false on error, in which case the error log is updated. The error log can be retrieved with al_get_shader_log(3).

SINCE

5.1.0

SEE ALSO

al_attach_shader_source_file(3), al_build_shader(3), al_get_default_shader_source(3), al_get_shader_log(3), ALLEGRO_PRIM_ATTR(3)