[Mesa-dev] [PATCH 6/9] glsl: implement mid3 built-in function

[Mario Rugiero]

Why not computing the max3(min(x,y),min(x,z),min(y,z))?

For the six possible cases:
x < y < z --> max(x, x, y) -> y ==> works
x < z < y --> max(x, z, z) -> z ==> works
y < x < z --> max(y, x, y) -> x ==> works
y < z < x --> max(y, z, y) -> z ==> works
z < x < y --> max(x, z, z) -> x ==> works
z < y < x --> max(y, z, z) -> y ==> works


2013/12/11 Kenneth Graunke <kenneth at whitecape.org>

> On 12/10/2013 02:43 PM, =?UTF-8?q?Maxence=20Le=20Dor=C3=A9?= <Maxence Le
> Doré> wrote:
> > ---
> >  src/glsl/builtin_functions.cpp | 44
> ++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 44 insertions(+)
> >
> > diff --git a/src/glsl/builtin_functions.cpp
> b/src/glsl/builtin_functions.cpp
> > index 1f21a37..b9beffd 100644
> > --- a/src/glsl/builtin_functions.cpp
> > +++ b/src/glsl/builtin_functions.cpp
> > @@ -404,6 +404,7 @@ private:
> >
> >     ir_expression *min3_expr(ir_variable *x, ir_variable *y, ir_variable
> *z);
> >     ir_expression *max3_expr(ir_variable *x, ir_variable *y, ir_variable
> *z);
> > +   ir_expression *mid3_expr(ir_variable *x, ir_variable *y, ir_variable
> *z);
> >
> >     /**
> >      * Call function \param f with parameters specified as the linked
> > @@ -589,6 +590,11 @@ private:
> >                                  const glsl_type *y_type,
> >                                  const glsl_type *z_type);
> >
> > +   ir_function_signature *_mid3(builtin_available_predicate avail,
> > +                                const glsl_type *x_type,
> > +                                const glsl_type *y_type,
> > +                                const glsl_type *z_type);
> > +
> >  #undef B0
> >  #undef B1
> >  #undef B2
> > @@ -2159,6 +2165,23 @@ builtin_builder::create_builtins()
> >                  _max3(shader_trinary_mimax, glsl_type::uvec4_type,
> glsl_type::uvec4_type, glsl_type::uvec4_type),
> >                  NULL);
> >
> > +   add_function("mid3",
> > +                _mid3(shader_trinary_mimax, glsl_type::float_type,
> glsl_type::float_type, glsl_type::float_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::vec2_type,
> glsl_type::vec2_type, glsl_type::vec2_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::vec3_type,
> glsl_type::vec3_type, glsl_type::vec3_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::vec4_type,
> glsl_type::vec4_type, glsl_type::vec4_type),
> > +
> > +                _mid3(shader_trinary_mimax, glsl_type::int_type,
> glsl_type::int_type, glsl_type::int_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::ivec2_type,
> glsl_type::ivec2_type, glsl_type::ivec2_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::ivec3_type,
> glsl_type::ivec3_type, glsl_type::ivec3_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::ivec4_type,
> glsl_type::ivec4_type, glsl_type::ivec4_type),
> > +
> > +                _mid3(shader_trinary_mimax, glsl_type::uint_type,
> glsl_type::uint_type, glsl_type::uint_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::uvec2_type,
> glsl_type::uvec2_type, glsl_type::uvec2_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::uvec3_type,
> glsl_type::uvec3_type, glsl_type::uvec3_type),
> > +                _mid3(shader_trinary_mimax, glsl_type::uvec4_type,
> glsl_type::uvec4_type, glsl_type::uvec4_type),
> > +                NULL);
> > +
> >  #undef F
> >  #undef FI
> >  #undef FIU
> > @@ -2386,6 +2409,12 @@ builtin_builder::max3_expr(ir_variable *x,
> ir_variable *y, ir_variable *z)
> >     return max(x, max(y,z));
> >  }
> >
> > +ir_expression *
> > +builtin_builder::mid3_expr(ir_variable *x, ir_variable *y, ir_variable
> *z)
> > +{
> > +   return max(min(x, y), min(y, z));
>
> This is broken if y is the median.  Consider the following cases:
>
> x < y < z --> max(x, y) -> y ==> works
> x < z < y --> max(x, z) -> z ==> works
> y < x < z --> max(y, y) -> y ==> broken (selects least, not median)
> y < z < x --> max(y, y) -> y ==> broken (selects least, not median)
> z < x < y --> max(x, z) -> x ==> works
> z < y < x --> max(y, z) -> y ==> works
>
> > +}
> > +
> >  ir_call *
> >  builtin_builder::call(ir_function *f, ir_variable *ret, exec_list
> params)
> >  {
> > @@ -4086,6 +4115,21 @@
> builtin_builder::_max3(builtin_available_predicate avail,
> >     return sig;
> >  }
> >
> > +ir_function_signature *
> > +builtin_builder::_mid3(builtin_available_predicate avail,
> > +                       const glsl_type *x_type, const glsl_type *y_type,
> > +                       const glsl_type *z_type)
> > +{
> > +   ir_variable *x = in_var(x_type, "x");
> > +   ir_variable *y = in_var(y_type, "y");
> > +   ir_variable *z = in_var(z_type, "z");
> > +   MAKE_SIG(x_type, avail, 3, x, y, z);
> > +
> > +   body.emit(ret(mid3_expr(x, y, z)));
> > +
> > +   return sig;
> > +}
> > +
> >  /** @} */
> >
> >
>  /******************************************************************************/
> >
>
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