Re: [AD] shader variable names

[SiegeLord <slabode@xxxxxxxxxx>]

So I talked on IRC with Trent and we concluded that the macros are a 
mistake because they never should be used from the user code (as macros 
or as strings).

There are two types of variables that are used by the shader addon. 
First there are ones that vary from vertex to vertex (al_pos, al_color, 
al_texcoord), which come from vertex data and there is no API to use 
those strings (instead there are al_set_shader_vertex_array, 
al_set_shader_color_array and al_set_shader_texcoord_array). As names, 
they are only used from GLSL shaders (HLSL shaders use a different 
mechanism altogether), so C macros for them are completely meaningless 
(with a tiniest exception of using them inside C string literals to 
specify shader definition, which I personally think makes for ugly code).

The second type are the uniforms (al_projview_matrix, al_use_tex, 
al_tex, al_use_tex_matrix, al_tex_matrix) which do not vary per vertex. 
There is an API to set them, but it won't do anything usually because 
the Allegro drawing code sets them. You can go 
al_set_shader_sampler(shader, ALLEGRO_SHADER_VAR_TEX, new_texture, 0), 
but since Allegro code resets it before drawing you'll have accomplished 
nothing. Again, you can safely use these macros inside the shader 
sources (this time it works for both HLSL and GLSL) that are specified 
as string literals.

So I think these macros should either be gone, or not be public because 
their usage outside the string literal shader definitions is always a 
mistake.

-SL