[Mesa-dev] [PATCH 1/2] gallivm: Add no_rho_opt debug option

[Brian Paul]

On 04/16/2013 01:07 PM, sroland at vmware.com wrote:
> From: Roland Scheidegger<sroland at vmware.com>
>
> This will calculate rho correctly as
> sqrt(max((ds/dx)^2 + (dt/dx)^2 + (dr/dx)^2), (ds/dx)^2 + (dt/dx)^2 + (dr/dx)^2))
> instead of max(|ds/dx|,|dt/dx|,|dr/dx|,|ds/dy|,|dt/dy,|dr/dy|)
> (for 3 coords - 2 coords work analogous, for 1 coord there's no point doing
> the exact version), for both implicit and explicit derivatives.
> While such approximation seems to be allowed in OpenGL some APIs may be less
> forgiving, and the error can be quite large (sqrt(2) for 2 coords, sqrt(3) for
> 3 coords so wrong by nearly one mip level in the latter case).
> This also helps to single out "real" bugs from "expected" ones, so it is debug
> only (though at least combined with no_brilinear I didn't really see much of a
> performance difference but only tested with a debug build - at least with
> implicit mipmaps the instruction count is almost exactly the same though the
> instructions are more complex (1 sqrt and mul/adds instead of and/max mostly).
> The code when the option isn't set stays exactly the same.

It sounds like a better name for the option would be something like 
"sqrt_rho" because you're just computing rho with more precision.


> ---
>   src/gallium/auxiliary/gallivm/lp_bld_debug.h  |    3 +-
>   src/gallium/auxiliary/gallivm/lp_bld_init.c   |    1 +
>   src/gallium/auxiliary/gallivm/lp_bld_sample.c |  299 +++++++++++++++----------
>   3 files changed, 185 insertions(+), 118 deletions(-)
>
> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_debug.h b/src/gallium/auxiliary/gallivm/lp_bld_debug.h
> index da873f3..b65a1f7 100644
> --- a/src/gallium/auxiliary/gallivm/lp_bld_debug.h
> +++ b/src/gallium/auxiliary/gallivm/lp_bld_debug.h
> @@ -42,7 +42,8 @@
>   #define GALLIVM_DEBUG_NO_OPT        (1<<  3)
>   #define GALLIVM_DEBUG_PERF          (1<<  4)
>   #define GALLIVM_DEBUG_NO_BRILINEAR  (1<<  5)
> -#define GALLIVM_DEBUG_GC            (1<<  6)
> +#define GALLIVM_DEBUG_NO_RHO_OPT    (1<<  6)

GALLIVM_DEBUG_SQRT_RHO?


Looks good otherwise.

-Brian