css: Add helper functions

We need to be able to translate css color spaces into gdk color
states, and css hue interplation into gsk hue interpolation.

gtk/gtkcsscolor.c

@@ -1167,6 +1167,46 @@ gtk_css_color_interpolation_method_print (GtkCssColorSpace        in,
 /* }}} */
 /* {{{ GdkColor conversion */
 
+/*< private >
+ * gtk_css_color_space_get_color_state:
+ * @color_space: a CSS color space
+ *
+ * Returns the best-matching GdkColorState for a given CSS color
+ * space.
+ *
+ * Note that we don't guarantee a 1:1 match between CSS color
+ * spaces and color states, so conversion of the color may
+ * still be necessary.
+ *
+ * Returns: (transfer none): the `GdkColorState`
+ */
+GdkColorState *
+gtk_css_color_space_get_color_state (GtkCssColorSpace color_space)
+{
+  switch (color_space)
+    {
+    case GTK_CSS_COLOR_SPACE_SRGB:
+    case GTK_CSS_COLOR_SPACE_HSL:
+    case GTK_CSS_COLOR_SPACE_HWB:
+    case GTK_CSS_COLOR_SPACE_OKLAB:
+    case GTK_CSS_COLOR_SPACE_OKLCH:
+      return GDK_COLOR_STATE_SRGB;
+
+    case GTK_CSS_COLOR_SPACE_SRGB_LINEAR:
+      return GDK_COLOR_STATE_SRGB_LINEAR;
+
+    case GTK_CSS_COLOR_SPACE_REC2020:
+    case GTK_CSS_COLOR_SPACE_DISPLAY_P3:
+    case GTK_CSS_COLOR_SPACE_XYZ:
+    case GTK_CSS_COLOR_SPACE_REC2100_PQ:
+      return GDK_COLOR_STATE_REC2100_PQ;
+      break;
+
+    default:
+      g_assert_not_reached ();
+    }
+}
+
 void
 gtk_css_color_to_color (const GtkCssColor *css,
                         GdkColor          *color)
@@ -1211,5 +1251,11 @@ gtk_css_color_to_color (const GtkCssColor *css,
     }
 }
 
+GskHueInterpolation
+gtk_css_hue_interpolation_to_hue_interpolation (GtkCssHueInterpolation interp)
+{
+  return (GskHueInterpolation) interp;
+}
+
 /* }}} */
 /* vim:set foldmethod=marker expandtab: */

gtk/gtkcsscolorprivate.h

@@ -23,6 +23,7 @@
 #include "gtk/css/gtkcssparserprivate.h"
 #include "gtkcsstypesprivate.h"
 #include "gdk/gdkcolorprivate.h"
+#include "gsk/gskrendernodeprivate.h"
 
 G_BEGIN_DECLS
 
@@ -106,6 +107,8 @@ void gtk_css_color_space_get_coord_range (GtkCssColorSpace  color_space,
                                           float            *lower,
                                           float            *upper);
 
+GdkColorState *gtk_css_color_space_get_color_state (GtkCssColorSpace color_space);
+
 gboolean gtk_css_color_interpolation_method_can_parse (GtkCssParser *parser);
 
 gboolean gtk_css_color_interpolation_method_parse (GtkCssParser           *parser,
@@ -116,6 +119,8 @@ void gtk_css_color_interpolation_method_print (GtkCssColorSpace        in,
                                                GtkCssHueInterpolation  interp,
                                                GString                *string);
 
+GskHueInterpolation gtk_css_hue_interpolation_to_hue_interpolation (GtkCssHueInterpolation interp);
+
 static inline gboolean
 gtk_css_color_is_clear (const GtkCssColor *color)
 {