[Mesa-dev] [PATCH] util: fix DXT1 RGBA texture compression if the source color is (0, 0, 0, 0)

[Roland Scheidegger]

Marek,

I'm not sure I agree here. If there's a bug in the lib, it should be 
fixed there, not tried to be worked around (correctly or not). And the 
bug has been there for years so it can't be suddenly that important. One 
version of the library is for instance 
cgit.freedesktop.org/~cbrill/libtxc_dxtn/ you could try to get a fix in 
there.

Roland


On 02/16/2011 03:43 AM, Marek Olšák wrote:
> Ideally we should fix this in libtxc_dxtn, but there is no central
> repository for that library, no versioning, and no official releases,
> and I am pretty sure that nobody would update that lib just to get this
> fix. Putting this fix in Mesa ensures that it will find its way to
> users, which is important.
>
> Marek
>
> On Wed, Feb 16, 2011 at 4:18 AM, Marek Olšák <maraeo at gmail.com
> <mailto:maraeo at gmail.com>> wrote:
>
>     This is a workaround for a bug in libtxc_dxtn.
>
>     Fixes:
>     - piglit/GL_EXT_texture_compression_s3tc/fbo-generatemipmap-formats
>     ---
>       src/gallium/auxiliary/util/u_format_s3tc.c |   16 ++++++++++++++--
>       1 files changed, 14 insertions(+), 2 deletions(-)
>
>     diff --git a/src/gallium/auxiliary/util/u_format_s3tc.c
>     b/src/gallium/auxiliary/util/u_format_s3tc.c
>     index bb989c2..31288e3 100644
>     --- a/src/gallium/auxiliary/util/u_format_s3tc.c
>     +++ b/src/gallium/auxiliary/util/u_format_s3tc.c
>     @@ -416,8 +416,20 @@ util_format_dxt1_rgba_pack_rgba_8unorm(uint8_t
>     *dst_row, unsigned dst_stride,
>               uint8_t tmp[4][4][4];  /* [bh][bw][comps] */
>               for(j = 0; j < bh; ++j) {
>                  for(i = 0; i < bw; ++i) {
>     -               for(k = 0; k < comps; ++k) {
>     -                  tmp[j][i][k] = src[(y +
>     j)*src_stride/sizeof(*src) + (x + i)*comps + k];
>     +               const uint8_t *srcp = &src[(y +
>     j)*src_stride/sizeof(*src) + (x + i)*comps];
>     +               /* Workaround for a bug in libtxc_dxtn.
>     +                * If the color is (0,0,0,0), it is compressed as
>     (0,0,0,1),
>     +                * which is incorrect. Any other (x,y,z,0) color is
>     compressed
>     +                * correctly as (0,0,0,0), so let's use (1,0,0,0). */
>     +               if (srcp[0] == 0 && srcp[1] == 0 && srcp[2] == 0 &&
>     srcp[3] == 0) {
>     +                  tmp[j][i][0] = 255;
>     +                  tmp[j][i][1] = 0;
>     +                  tmp[j][i][2] = 0;
>     +                  tmp[j][i][3] = 0;
>     +               } else {
>     +                  for(k = 0; k < comps; ++k) {
>     +                     tmp[j][i][k] = srcp[k];
>     +                  }
>                     }
>                  }
>               }
>     --
>     1.7.1
>
>