[PATCH 2/3] xrandr: fix gamma == 1.0 && sigbits != 8

[walter harms]

Am 14.08.2012 01:25, schrieb Andy Ritger:
> The gamma-correction lookup table managed through XRR[GS]etCrtcGamma is
> 2^n in size, where 'n' is the number of significant bits in the X Color.
> Each element in the gamma-correction lookup table is a 16:16:16 X Color
> (i.e., in the range [0,65536) ).  The significant bits of each component
> of each element in the lookup table are programmed into the hardware
> lookup table.  Meaningful values in the gamma-correction lookup table
> are thus in the range [0,2^sigbits), where all values are shifted into
> the MSBs (i.e., left shifted by (16 - sigificant bits)).
> 
> Signed-off-by: Andy Ritger <aritger at nvidia.com>
> Reviewed-by: Aaron Plattner <aplattner at nvidia.com>
> ---
>  xrandr.c |   15 +++++++++++----
>  1 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/xrandr.c b/xrandr.c
> index 75ed2ee..5709ded 100644
> --- a/xrandr.c
> +++ b/xrandr.c
> @@ -1323,7 +1323,7 @@ set_gamma(void)
>      output_t	*output;
>  
>      for (output = outputs; output; output = output->next) {
> -	int i, size;
> +	int i, size, shift;
>  	crtc_t *crtc;
>  	XRRCrtcGamma *gamma;
>  	float gammaRed;
> @@ -1347,6 +1347,13 @@ set_gamma(void)
>  	    continue;
>  	}
>  
> +	/*
> +	 * The hardware color lookup table has a number of significant
> +	 * bits equal to ffs(size) - 1; shift values so that they
> +	 * occupy the MSBs of the 16-bit X Color.
> +	 */
> +	shift = 16 - (ffs(size) - 1);
> +

       you assume ffs(size) >16, is that save ?

	re,
 	wh


>  	gamma = XRRAllocGamma(size);
>  	if (!gamma) {
>  	    fatal("Gamma allocation failed.\n");
> @@ -1366,21 +1373,21 @@ set_gamma(void)
>  
>  	for (i = 0; i < size; i++) {
>  	    if (gammaRed == 1.0 && output->brightness == 1.0)
> -		gamma->red[i] = (i << 8) + i;
> +		gamma->red[i] = (i << shift);
>  	    else
>  		gamma->red[i] = dmin(pow((double)i/(double)(size - 1),
>  					 gammaRed) * output->brightness,
>  				     1.0) * 65535.0;
>  
>  	    if (gammaGreen == 1.0 && output->brightness == 1.0)
> -		gamma->green[i] = (i << 8) + i;
> +		gamma->green[i] = (i << shift);
>  	    else
>  		gamma->green[i] = dmin(pow((double)i/(double)(size - 1),
>  					   gammaGreen) * output->brightness,
>  				       1.0) * 65535.0;
>  
>  	    if (gammaBlue == 1.0 && output->brightness == 1.0)
> -		gamma->blue[i] = (i << 8) + i;
> +		gamma->blue[i] = (i << shift);
>  	    else
>  		gamma->blue[i] = dmin(pow((double)i/(double)(size - 1),
>  					  gammaBlue) * output->brightness,