#include <allegro5/allegro.h> bool al_attach_shader_source(ALLEGRO_SHADER *shader, ALLEGRO_SHADER_TYPE type, const char *source)
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:
- matrix for Allegro’s orthographic projection multiplied by the al_use_transform(3) matrix. The type is mat4 in GLSL, and float4x4 in HLSL.
- whether or not to use the bound texture. The type is bool in both GLSL and HLSL.
- the texture if one is bound. The type is sampler2D in GLSL and texture in HLSL.
- whether or not to use a texture matrix (used by the primitives addon). The type is bool in both GLSL and HLSL.
- 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.
For GLSL shaders the vertex attributes are passed using the following variables:
- vertex position attribute. Type is vec4.
- vertex texture coordinate attribute. Type is vec2.
- vertex color attribute. Type is vec4.
- 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:
- vertex position attribute. Type is float4.
- vertex texture coordinate attribute. Type is float2.
- 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”
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).
|Allegro reference manual|