[Mesa-dev] [PATCH 10/10] glsl/linker: Pack between varyings.

[Eric Anholt]

Paul Berry <stereotype441 at gmail.com> writes:

> This patch implements varying packing between varyings.
>
> Previously, each varying occupied components 0 through N-1 of its
> assigned varying slot, so there was no way to pack two varyings into
> the same slot.  For example, if the varyings were a float, a vec2, a
> vec3, and another vec2, they would be stored as follows:
>
>  <----slot1----> <----slot2----> <----slot3----> <----slot4---->  slots
>   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *   *
>  flt  x   x   x  <vec2->  x   x  <--vec3--->  x  <vec3->  x   x   varyings

That's a funny-looking vec3 you've got here.       ^^^^^^^

> -      if (producer_var->type->is_array()) {
> -         const unsigned slots = producer_var->type->length
> -            * producer_var->type->fields.array->matrix_columns;
> +      /* Advance to the next slot if this varying has a different packing
> +       * class than the previous one, and we're not already on a slot
> +       * boundary.
> +       */
> +      if (i > 0 && generic_location % 4 != 0 &&
> +          this->matches[i - 1].packing_class
> +          != this->matches[i].packing_class) {
> +         generic_location += 4 - generic_location % 4;

Grab an align macro from anywhere else (we really need to just stuff
something in macros.h), then "generic_location = ALIGN(generic_location,
4)", and you can skip checking for already being on a slot boundary.

>  /**
> + * Compute the number of components that this variable will occupy when
> + * properly packed.
> + */
> +unsigned
> +varying_matches::compute_num_components(ir_variable *var)
> +{
> +   const glsl_type *type = var->type;
> +   unsigned multipiler = 1;
> +
> +   if (type->is_array()) {
> +      multipiler *= type->length;
> +      type = type->fields.array;
> +   }
> +
> +   /* FINISHME: Support for "varying" records in GLSL 1.50. */
> +   assert(!type->is_record());
> +
> +   return multipiler * type->components();

"multiplier"

I think this function is just type->component_slots(), though, at the
expense of using a different meaning of the term "slot" from the rest of
the code you're working on.
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