cicp: Fill in some more transfer functions

Handle gamma 2.2 and gamma 2.8.

gdk/gdkcicpparams.c

@@ -160,10 +160,10 @@ gdk_cicp_params_class_init (GdkCicpParamsClass *klass)
    * GdkCicpParams:color-primaries:
    *
    * Supported values:
-   * 1 - sRGB
+   * 1 - BT.709 / sRGB
    * 2 - unspecified
    * 5 - PAL
-   * 6,7 - NTSC
+   * 6,7 - BT.601 / NTSC
    * 9 - BT.2020
    * 10 - CIE XYZ
    * 12 - Display P3
@@ -179,12 +179,14 @@ gdk_cicp_params_class_init (GdkCicpParamsClass *klass)
    * GdkCicpParams:transfer-function:
    *
    * Supported values:
-   * 1,6,14,15 - BT.709
+   * 1,6,14,15 - BT.709, BT.601, BT.2020
    * 2 - unspecified
+   * 4 - gamma 2.2
+   * 5 - gamma 2.8
    * 8 - linear
    * 13 - sRGB
-   * 16 - PQ
-   * 18 - HLG
+   * 16 - BT.2100 PQ
+   * 18 - BT.2100 HLG
    *
    * Since: 4.16
    */

gdk/gdkcolordefs.h

@@ -38,6 +38,30 @@ srgb_eotf (float v)
     return v / 12.92f;
 }
 
+static inline float
+gamma22_oetf (float v)
+{
+  return powf (v, 1.f / 2.2f);
+}
+
+static inline float
+gamma22_eotf (float v)
+{
+  return powf (v, 2.2f);
+}
+
+static inline float
+gamma28_oetf (float v)
+{
+  return powf (v, 1.f / 2.8f);
+}
+
+static inline float
+gamma28_eotf (float v)
+{
+  return powf (v, 2.8f);
+}
+
 static inline float
 pq_eotf (float v)
 {

gdk/gdkcolorstate.c

@@ -626,6 +626,14 @@ gdk_color_state_new_for_cicp (const GdkCicp  *cicp,
       eotf = bt709_eotf;
       oetf = bt709_oetf;
       break;
+    case 4:
+      eotf = gamma22_eotf;
+      oetf = gamma22_oetf;
+      break;
+    case 5:
+      eotf = gamma28_eotf;
+      oetf = gamma28_oetf;
+      break;
     case 8:
       eotf = NONE;
       oetf = NONE;

testsuite/gdk/colorstate-internal.c

@@ -18,6 +18,8 @@ TransferTest transfers[] = {
   { "pq", pq_oetf, pq_eotf },
   { "bt709", bt709_oetf, bt709_eotf },
   { "hlg", hlg_oetf, hlg_eotf },
+  { "gamma22", gamma22_oetf, gamma22_eotf },
+  { "gamma28", gamma28_oetf, gamma28_eotf },
 };
 
 static void