[Mesa-dev] [PATCH] meta: Disable dithering during glGenerateMipmap

[Kenneth Graunke]

On Thursday, December 29, 2016 1:25:57 PM PST Chad Versace wrote:
> Fixes tests 'dEQP-GLES3.functional.texture.mipmap.*.generate.rgba5551*' on
> Intel Broadwell 0x1616.
> 
> The GL 4.5 spec describes the algorithm of glGenerateMipmap as:
> 
>     The contents of the derived images are computed by repeated, filtered
>     reduction of the level base image.  [...] No particular filter algorithm is
>     required, though a box filter is recommended as the default filter.
> 
> Consider a texture for which all pixels are identical at level 0.
> From the spec's description above, one may reasonably assume that the "filtered
> reduction" of level 0 produces a new miplevel for which again all pixels are
> identical. For any 2x2 subspan of identical pixels, it is difficult to see how
> the "filtered reduction" of that subspan can produce a pixel that differs from
> the source pixels.
> 
> Dithering during _mesa_meta_GenerateMipmap() violated that reasonable
> assumption.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=99210
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/mesa/drivers/common/meta_generate_mipmap.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/src/mesa/drivers/common/meta_generate_mipmap.c b/src/mesa/drivers/common/meta_generate_mipmap.c
> index bbe9d6d886..55093e9553 100644
> --- a/src/mesa/drivers/common/meta_generate_mipmap.c
> +++ b/src/mesa/drivers/common/meta_generate_mipmap.c
> @@ -182,6 +182,7 @@ _mesa_meta_GenerateMipmap(struct gl_context *ctx, GLenum target,
>  
>     _mesa_meta_begin(ctx, MESA_META_ALL & ~MESA_META_DRAW_BUFFERS);
>     _mesa_ColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
> +   _mesa_Disable(GL_DITHER);
>  
>     /* Choose between glsl version and fixed function version of
>      * GenerateMipmap function.
> 

Good catch!  That makes sense.  I verified that the meta begin flags
will restore the dither mode at the end.

Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 833 bytes
Desc: This is a digitally signed message part.
URL: <https://lists.freedesktop.org/archives/mesa-dev/attachments/20161229/2c27bf9b/attachment-0001.sig>