[PATCH] xrandr: use full range for gamma table generation

[Stéphane Marchesin]

And pushed.


On Fri, Apr 18, 2014 at 8:19 PM, Stéphane Marchesin <
stephane.marchesin at gmail.com> wrote:

>
>
>
> On Tue, Apr 1, 2014 at 8:02 PM, <dbehr at chromium.org> wrote:
>
>> From: Dominik Behr <dbehr at chromium.org>
>>
>> Calculate gamma table using full [0,65536) range and do not make any
>> assumptions about relation of gamma table size and significant bits.
>>
>> Gamma table size has nothing to do with number of significant bits in
>> hardware.
>> In particular we are dealing now with gamma table that has 17 entries and
>> 8
>> bit precision, there are other GPUs with 10 bit precision and less than
>> 256
>> entries using partial linear approximation. Deriving assumed gamma table
>> significant bits from size of gamma table leads to incorrect calculations
>> and
>> loss of precision. Also XRandR specification never mentions that gamma
>> tables
>> need to be power of 2.
>>
>> Signed-off-by: Dominik Behr <dbehr at chromium.org>
>>
>
> Reviewed-by: Stéphane Marchesin <marcheu at chromium.org>
>
> ---
>>  xrandr.c | 25 +++++++------------------
>>  1 file changed, 7 insertions(+), 18 deletions(-)
>>
>> diff --git a/xrandr.c b/xrandr.c
>> index c51bee3..7a5fa30 100644
>> --- a/xrandr.c
>> +++ b/xrandr.c
>> @@ -1394,7 +1394,7 @@ set_gamma(void)
>>      output_t   *output;
>>
>>      for (output = all_outputs; output; output = output->next) {
>> -       int i, size, shift;
>> +       int i, size;
>>         crtc_t *crtc;
>>         XRRCrtcGamma *crtc_gamma;
>>         float gammaRed;
>> @@ -1429,14 +1429,6 @@ set_gamma(void)
>>             continue;
>>         }
>>
>> -       /*
>> -        * The hardware color lookup table has a number of significant
>> -        * bits equal to ffs(size) - 1; compute all values so that
>> -        * they are in the range [0,size) then shift the values so
>> -        * that they occupy the MSBs of the 16-bit X Color.
>> -        */
>> -       shift = 16 - (ffs(size) - 1);
>> -
>>         crtc_gamma = XRRAllocGamma(size);
>>         if (!crtc_gamma) {
>>             fatal("Gamma allocation failed.\n");
>> @@ -1456,28 +1448,25 @@ set_gamma(void)
>>
>>         for (i = 0; i < size; i++) {
>>             if (gammaRed == 1.0 && output->brightness == 1.0)
>> -               crtc_gamma->red[i] = i;
>> +               crtc_gamma->red[i] = (double)i / (double)(size - 1) *
>> 65535.0;
>>             else
>>                 crtc_gamma->red[i] = dmin(pow((double)i/(double)(size -
>> 1),
>>                                               gammaRed) *
>> output->brightness,
>> -                                         1.0) * (double)(size - 1);
>> -           crtc_gamma->red[i] <<= shift;
>> +                                         1.0) * 65535.0;
>>
>>             if (gammaGreen == 1.0 && output->brightness == 1.0)
>> -               crtc_gamma->green[i] = i;
>> +               crtc_gamma->green[i] = (double)i / (double)(size - 1) *
>> 65535.0;
>>             else
>>                 crtc_gamma->green[i] = dmin(pow((double)i/(double)(size -
>> 1),
>>                                                 gammaGreen) *
>> output->brightness,
>> -                                           1.0) * (double)(size - 1);
>> -           crtc_gamma->green[i] <<= shift;
>> +                                           1.0) * 65535.0;
>>
>>             if (gammaBlue == 1.0 && output->brightness == 1.0)
>> -               crtc_gamma->blue[i] = i;
>> +               crtc_gamma->blue[i] = (double)i / (double)(size - 1) *
>> 65535.0;
>>             else
>>                 crtc_gamma->blue[i] = dmin(pow((double)i/(double)(size -
>> 1),
>>                                                gammaBlue) *
>> output->brightness,
>> -                                          1.0) * (double)(size - 1);
>> -           crtc_gamma->blue[i] <<= shift;
>> +                                          1.0) * 65535.0;
>>         }
>>
>>         XRRSetCrtcGamma(dpy, crtc->crtc.xid, crtc_gamma);
>> --
>> 1.9.1.423.g4596e3a
>>
>> _______________________________________________
>> xorg-devel at lists.x.org: X.Org development
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>>
>
>
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