[Cogl] [PATCH] gl: bind position attribute to location 0

[Neil Roberts]

I think this patch makes sense to land but it does highlight the issue
that we are effectively requiring applications to use cogl_position_in
if they want to work on GL2 because if they were to entirely use their
own attributes then they would have no way to force a non-constant
attribute into position zero. I don't suppose there's any particular
reason not to use cogl_position_in in practice unless you are converting
existing code that uses a custom attribute. However I wonder if we
should consider documenting that and maybe even make
_cogl_flush_attributes_state give a warning if there is no non-constant
binding for cogl_position_in.

> +      /* XXX: OpenGL as a special case requires the vertex position to
> +       * be bound to generic attribute 0 so for simplicity we
> +       * unconditionally bind the cogl_position_in attribute here...
> +       */
> +      GE( ctx, glBindAttribLocation (program_state->program, 0,
> "cogl_position_in"));

It would be nice if you could make this line fit in 80 characters.

> +  snippet = cogl_snippet_new (COGL_SNIPPET_HOOK_VERTEX,
> +                              "attribute vec4 color;",
> +                              "cogl_color_out = vec4 (0.0, 1.0, 0, 1.0);");
> +  cogl_pipeline_add_snippet (pipeline2, snippet);

That 0 should probably be 0.0 or it might not compile on fussy drivers.

Reviewed-by: Neil Roberts <neil at linux.intel.com>

Regards,
- Neil
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