color: Add gdk_color_clamp_to_gamut

This is a very primitive way to get a color into gamut: just
clamp it.

Tests included.

gdk/gdkcolor.c

@@ -298,4 +298,46 @@ gdk_color_to_string (const GdkColor *self)
   return g_string_free (string, FALSE);
 }
 
+gboolean
+gdk_color_in_gamut (const GdkColor *self,
+                    GdkColorState  *color_state)
+{
+  float values[4];
+  const float *range;
 
+  gdk_color_to_float (self, color_state, values);
+
+  range = gdk_color_state_get_range (color_state);
+
+  return range[0] <= values[0] && values[0] <= range[1] &&
+         range[2] <= values[1] && values[1] <= range[3] &&
+         range[4] <= values[2] && values[2] <= range[5] &&
+         range[6] <= values[3] && values[3] <= range[7];
+}
+
+void
+gdk_color_clamp_to_gamut (GdkColor      *self,
+                          GdkColorState *color_state)
+{
+  GdkColor tmp;
+  const float *range;
+
+  gdk_color_to_float (self, color_state, tmp.values);
+
+  range = gdk_color_state_get_range (color_state);
+
+  if (range[0] > tmp.values[0] || tmp.values[0] > range[1] ||
+      range[2] > tmp.values[1] || tmp.values[1] > range[3] ||
+      range[4] > tmp.values[2] || tmp.values[2] > range[5] ||
+      range[6] > tmp.values[3] || tmp.values[3] > range[7])
+    {
+      tmp.color_state = color_state;
+
+      tmp.values[0] = CLAMP (tmp.values[0], range[0], range[1]);
+      tmp.values[1] = CLAMP (tmp.values[1], range[2], range[3]);
+      tmp.values[2] = CLAMP (tmp.values[2], range[4], range[5]);
+      tmp.values[3] = CLAMP (tmp.values[3], range[6], range[7]);
+
+      gdk_color_to_float (&tmp, self->color_state, self->values);
+    }
+}

gdk/gdkcolorprivate.h

@@ -102,6 +102,12 @@ void              gdk_color_print               (const GdkColor         *self,
 
 char *            gdk_color_to_string           (const GdkColor         *self);
 
+gboolean          gdk_color_in_gamut            (const GdkColor         *self,
+                                                 GdkColorState          *color_state);
+
+void              gdk_color_clamp_to_gamut      (GdkColor               *self,
+                                                 GdkColorState          *color_state);
+
 #include "gdkcolorimpl.h"
 
 G_END_DECLS

testsuite/gdk/colorstate-internal.c

@@ -210,6 +210,36 @@ test_color_mislabel (void)
   g_assert_true (red1 != red2);
 }
 
+static void
+test_color_gamut (void)
+{
+  GdkColor color = GDK_COLOR_SRGB (1, 0, 0, 1);
+
+  g_assert_true (gdk_color_in_gamut (&color, GDK_COLOR_STATE_SRGB));
+  g_assert_true (gdk_color_in_gamut (&color, GDK_COLOR_STATE_SRGB_LINEAR));
+  g_assert_true (gdk_color_in_gamut (&color, GDK_COLOR_STATE_REC2100_PQ));
+  g_assert_true (gdk_color_in_gamut (&color, GDK_COLOR_STATE_REC2100_LINEAR));
+
+  gdk_color_finish (&color);
+
+  gdk_color_init (&color, GDK_COLOR_STATE_REC2100_PQ, (float[]) {0.9, 0.9, 0.9, 1});
+
+  g_assert_false (gdk_color_in_gamut (&color, GDK_COLOR_STATE_SRGB));
+  g_assert_false (gdk_color_in_gamut (&color, GDK_COLOR_STATE_SRGB_LINEAR));
+  g_assert_true (gdk_color_in_gamut (&color, GDK_COLOR_STATE_REC2100_PQ));
+  g_assert_true (gdk_color_in_gamut (&color, GDK_COLOR_STATE_REC2100_LINEAR));
+
+  gdk_color_clamp_to_gamut (&color, GDK_COLOR_STATE_SRGB);
+
+  /* clamping an out-of-gamut gray to srgb yields media white */
+  g_assert_cmpfloat_with_epsilon (color.red, 0.58, 0.001);
+  g_assert_cmpfloat_with_epsilon (color.green, 0.58, 0.001);
+  g_assert_cmpfloat_with_epsilon (color.blue, 0.58, 0.001);
+  g_assert_cmpfloat_with_epsilon (color.alpha, 1, 0.001);
+
+  gdk_color_finish (&color);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -242,6 +272,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/colorstate/matrix/srgb_to_rec2020", test_srgb_to_rec2020);
   g_test_add_func ("/colorstate/matrix/rec2020_to_srgb", test_rec2020_to_srgb);
   g_test_add_func ("/color/mislabel", test_color_mislabel);
+  g_test_add_func ("/color/gamut", test_color_gamut);
 
   return g_test_run ();
 }