[Mesa-dev] [PATCH] glsl: improve accuracy of atan()

[Erik Faye-Lund]

On Wed, Sep 24, 2014 at 1:35 PM, Erik Faye-Lund <kusmabite at gmail.com> wrote:
> Hm. Don't I need to expand this last immediate to a vector of
> type->components() size as well?
>
> If so, this patch should go on top:
>
> diff --git a/src/glsl/builtin_functions.cpp b/src/glsl/builtin_functions.cpp
> index 1820dd5..bfa46eb 100644
> --- a/src/glsl/builtin_functions.cpp
> +++ b/src/glsl/builtin_functions.cpp
> @@ -2749,13 +2749,11 @@ builtin_builder::do_atan(ir_factory &body,
> const glsl_type *type, ir_variable *r
>     /* range-reduction fixup */
>     body.emit(assign(tmp, add(tmp,
>                               csel(greater(abs(y_over_x),
> -                                          swizzle(imm(1.0f),
> -                                                  SWIZZLE_XXXX,
> -                                                  type->components())),
> +                                          imm(1.0f, type->components())),
>                                    add(mul(tmp,
>                                            imm(-2.0f)),
>                                        imm(M_PI_2f)),
> -                                  imm(0.0f)))));
> +                                  imm(0.0f, type->components())))));
>
>     /* sign fixup */
>     body.emit(assign(res, mul(tmp, sign(y_over_x))));

Ugh, it seems things fail piglit's shaders/glsl-fs-atan-1 pretty badly
on swrast.

../../src/mesa/program/ir_to_mesa.cpp:1426: virtual void
{anonymous}::ir_to_mesa_visitor::visit(ir_expression*): Assertion
`!"not supported"' failed.

Ugh, yeah. We don't seem to support ir_trip_csel on swrast, and
there's no attempt to lower it unless it's condition is constant 0 or
1 (in opt_algebraic.cpp). So yeah, this regresses there, but looking
at the other builtins, so does anything that uses gentype mix(gentype,
gentype, genBtype) etc. However, that's at least blocked by a GLSL
v130 check, which swrast does not support.

So, I've got some more work to do :/