[Mesa-dev] GLSL builtins constant constructor

[Paul Berry]

On 4 September 2011 14:49, Ian Romanick <idr at freedesktop.org> wrote:

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> On 09/04/2011 08:35 AM, Paul Berry wrote:
> > On 4 September 2011 06:20, Christoph Bumiller
> > <e0425955 at student.tuwien.ac.at <mailto:e0425955 at student.tuwien.ac.at>>
> > wrote:
> >
> >     I encountered some failures in piglit's tests of builtins because a
> >     vector constructor that is given only 1 single argument does not
> >     replicate the argument into the yzw components, for example:
> >
> >     diff --git a/src/glsl/builtins/ir/cosh b/src/glsl/builtins/ir/cosh
> >     index 45e0ae4..8bf3ad2 100644
> >     --- a/src/glsl/builtins/ir/cosh
> >     +++ b/src/glsl/builtins/ir/cosh
> >     @@ -9,21 +9,21 @@
> >        (signature vec2
> >          (parameters
> >            (declare (in) vec2 x))
> >     -     ((return (expression vec2 * (constant vec2 (0.5))
> >     +     ((return (expression vec2 * (constant vec2 (0.5, 0.5))
> >                     (expression vec2 +
> >                      (expression vec2 exp (var_ref x))
> >                      (expression vec2 exp (expression vec2 neg (var_ref
> >     x))))))))
> >        (signature vec3
> >          (parameters
> >            (declare (in) vec3 x))
> >
> >     Should the constructors or should all the builtin files be fixed ?
> >
> >
> > Thanks for noticing this, Christoph.  I wrote the tests for hyperbolic
> > trig functions a few weeks ago, and I've been waiting for some i965
> > churn to settle down before looping back to fix the bugs.
> >
> > Personally, I'd prefer to fix this bug by making the constant a scalar,
> > like this:
>
> I don't recall for sure, but, while that is valid GLSL, I don't think
> that's valid in the IR.  Did you try it?  I think you may have to wrap
> it in a swizzle, at which point it's probably better to use the correct
> vec# constructor.
>

Yes, I did try it, and it worked just fine.  Furthermore, the code in
ir_validate.cpp seems to indicate that multiplying a scalar by a vector is
allowed in GLSL IR:

   case ir_binop_add:
   case ir_binop_sub:
   case ir_binop_mul:
   case ir_binop_div:
   case ir_binop_mod:
   case ir_binop_min:
   case ir_binop_max:
   case ir_binop_pow:
      if (ir->operands[0]->type->is_scalar())
     assert(ir->operands[1]->type == ir->type);
      else if (ir->operands[1]->type->is_scalar())
     assert(ir->operands[0]->type == ir->type);
      else if (ir->operands[0]->type->is_vector() &&
           ir->operands[1]->type->is_vector()) {
     assert(ir->operands[0]->type == ir->operands[1]->type);
     assert(ir->operands[0]->type == ir->type);
      }
      break;

Also, as I noted in my previous email, this is what we do in several other
built-in functions, such as asin:

   (signature vec2
     (parameters
       (declare (in) vec2 x))
     ((return (expression vec2 *
           (expression vec2 sign (var_ref x))
           (expression vec2 -
        (constant float (1.5707964))
        (expression vec2 *
         (expression vec2 sqrt
          (expression vec2 -
           (constant float (1.0))
           (expression vec2 abs (var_ref x))))
         (expression vec2 +
          (constant float (1.5707964))
          (expression vec2 *
           (expression vec2 abs (var_ref x))
           (expression vec2 +
            (constant float (-0.21460183))
            (expression vec2 *
             (expression vec2 abs (var_ref x))
                     (expression vec2 +
                      (constant float (0.086566724))
                      (expression vec2 *
                       (expression vec2 abs (var_ref x))
                       (constant float (-0.03102955))
             ))))))))))))
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