[PATCH] Parse the color management parts of the EDID

[John Kåre Alsaker]

EDID parsing should probably be moved out of compositor-drm since other
backends can provide EDIDs too.


On Thu, May 2, 2013 at 10:38 PM, Richard Hughes <hughsient at gmail.com> wrote:

> This code was originally written by Soren Sandmann <sandmann at redhat.com>
> and was
> found here: http://people.gnome.org/~ssp/randr/edid-parse.c
>
> The code has been in use in gnome-settings-daemon for a couple of years
> now and
> is used to generate an Auto-EDID ICC profile if the screen has not been
> profiled
> with a calibration device.
>
> This will be used by the CMS plugins in the future, and so it makes sense
> being
> common code in compositor-drm.
> ---
>  src/compositor-drm.c | 56
> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 56 insertions(+)
>
> diff --git a/src/compositor-drm.c b/src/compositor-drm.c
> index f39096e..e4a1919 100644
> --- a/src/compositor-drm.c
> +++ b/src/compositor-drm.c
> @@ -136,11 +136,22 @@ struct drm_fb {
>         void *map;
>  };
>
> +struct drm_color_Yxy {
> +       double Y;
> +       double x;
> +       double y;
> +};
> +
>  struct drm_edid {
>         char eisa_id[13];
>         char monitor_name[13];
>         char pnp_id[5];
>         char serial_number[13];
> +       struct drm_color_Yxy whitepoint;
> +       struct drm_color_Yxy primary_red;
> +       struct drm_color_Yxy primary_green;
> +       struct drm_color_Yxy primary_blue;
> +       double gamma;
>  };
>
>  struct drm_output {
> @@ -1558,6 +1569,31 @@ edid_parse_string(const uint8_t *data, char text[])
>  #define EDID_OFFSET_SERIAL                             0x0c
>
>  static int
> +edid_get_bit(int in, int bit)
> +{
> +       return (in & (1 << bit)) >> bit;
> +}
> +
> +static int
> +edid_get_bits(int in, int begin, int end)
> +{
> +       int mask = (1 << (end - begin + 1)) - 1;
> +       return (in >> begin) & mask;
> +}
> +
> +static double
> +edid_decode_fraction(int high, int low)
> +{
> +       double result = 0.0;
> +       int i;
> +
> +       high = (high << 2) | low;
> +       for (i = 0; i < 10; ++i)
> +               result += edid_get_bit(high, i) * pow(2, i - 10);
> +       return result;
> +}
> +
> +static int
>  edid_parse(struct drm_edid *edid, const uint8_t *data, size_t length)
>  {
>         int i;
> @@ -1579,6 +1615,26 @@ edid_parse(struct drm_edid *edid, const uint8_t
> *data, size_t length)
>         edid->pnp_id[2] = 'A' + (data[EDID_OFFSET_PNPID + 1] & 0x1f) - 1;
>         edid->pnp_id[3] = '\0';
>
> +       /* get native gamma */
> +       if (data[0x17] == 0xff)
> +               edid->gamma = -1.0;
> +       else
> +               edid->gamma = (data[0x17] + 100.0) / 100.0;
> +
> +       /* get primaries and whitepoint */
> +       edid->primary_red.Y = 1.0f;
> +       edid->primary_red.x = edid_decode_fraction(data[0x1b],
> edid_get_bits(data[0x19], 6, 7));
> +       edid->primary_red.y = edid_decode_fraction(data[0x1c],
> edid_get_bits(data[0x19], 5, 4));
> +       edid->primary_green.Y = 1.0f;
> +       edid->primary_green.x = edid_decode_fraction(data[0x1d],
> edid_get_bits(data[0x19], 2, 3));
> +       edid->primary_green.y = edid_decode_fraction(data[0x1e],
> edid_get_bits(data[0x19], 0, 1));
> +       edid->primary_blue.Y = 1.0f;
> +       edid->primary_blue.x = edid_decode_fraction(data[0x1f],
> edid_get_bits(data[0x1a], 6, 7));
> +       edid->primary_blue.y = edid_decode_fraction(data[0x20],
> edid_get_bits(data[0x1a], 4, 5));
> +       edid->whitepoint.Y = 1.0f;
> +       edid->whitepoint.x = edid_decode_fraction(data[0x21],
> edid_get_bits(data[0x1a], 2, 3));
> +       edid->whitepoint.y = edid_decode_fraction(data[0x22],
> edid_get_bits(data[0x1a], 0, 1));
> +
>         /* maybe there isn't a ASCII serial number descriptor, so use this
> instead */
>         serial_number = (uint32_t) data[EDID_OFFSET_SERIAL + 0];
>         serial_number += (uint32_t) data[EDID_OFFSET_SERIAL + 1] * 0x100;
> --
> 1.8.2.1
>
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