GtkSymbolicColor: convert to/from hls when shading.

This makes shading equal to GtkStyle's.

gtk/gtksymboliccolor.c

@@ -292,6 +292,181 @@ gtk_symbolic_color_unref (GtkSymbolicColor *color)
     }
 }
 
+static void
+rgb_to_hls (gdouble *r,
+            gdouble *g,
+            gdouble *b)
+{
+  gdouble min;
+  gdouble max;
+  gdouble red;
+  gdouble green;
+  gdouble blue;
+  gdouble h, l, s;
+  gdouble delta;
+  
+  red = *r;
+  green = *g;
+  blue = *b;
+  
+  if (red > green)
+    {
+      if (red > blue)
+        max = red;
+      else
+        max = blue;
+      
+      if (green < blue)
+        min = green;
+      else
+        min = blue;
+    }
+  else
+    {
+      if (green > blue)
+        max = green;
+      else
+        max = blue;
+      
+      if (red < blue)
+        min = red;
+      else
+        min = blue;
+    }
+  
+  l = (max + min) / 2;
+  s = 0;
+  h = 0;
+  
+  if (max != min)
+    {
+      if (l <= 0.5)
+        s = (max - min) / (max + min);
+      else
+        s = (max - min) / (2 - max - min);
+      
+      delta = max -min;
+      if (red == max)
+        h = (green - blue) / delta;
+      else if (green == max)
+        h = 2 + (blue - red) / delta;
+      else if (blue == max)
+        h = 4 + (red - green) / delta;
+      
+      h *= 60;
+      if (h < 0.0)
+        h += 360;
+    }
+  
+  *r = h;
+  *g = l;
+  *b = s;
+}
+
+static void
+hls_to_rgb (gdouble *h,
+            gdouble *l,
+            gdouble *s)
+{
+  gdouble hue;
+  gdouble lightness;
+  gdouble saturation;
+  gdouble m1, m2;
+  gdouble r, g, b;
+  
+  lightness = *l;
+  saturation = *s;
+  
+  if (lightness <= 0.5)
+    m2 = lightness * (1 + saturation);
+  else
+    m2 = lightness + saturation - lightness * saturation;
+  m1 = 2 * lightness - m2;
+  
+  if (saturation == 0)
+    {
+      *h = lightness;
+      *l = lightness;
+      *s = lightness;
+    }
+  else
+    {
+      hue = *h + 120;
+      while (hue > 360)
+        hue -= 360;
+      while (hue < 0)
+        hue += 360;
+      
+      if (hue < 60)
+        r = m1 + (m2 - m1) * hue / 60;
+      else if (hue < 180)
+        r = m2;
+      else if (hue < 240)
+        r = m1 + (m2 - m1) * (240 - hue) / 60;
+      else
+        r = m1;
+      
+      hue = *h;
+      while (hue > 360)
+        hue -= 360;
+      while (hue < 0)
+        hue += 360;
+      
+      if (hue < 60)
+        g = m1 + (m2 - m1) * hue / 60;
+      else if (hue < 180)
+        g = m2;
+      else if (hue < 240)
+        g = m1 + (m2 - m1) * (240 - hue) / 60;
+      else
+        g = m1;
+      
+      hue = *h - 120;
+      while (hue > 360)
+        hue -= 360;
+      while (hue < 0)
+        hue += 360;
+      
+      if (hue < 60)
+        b = m1 + (m2 - m1) * hue / 60;
+      else if (hue < 180)
+        b = m2;
+      else if (hue < 240)
+        b = m1 + (m2 - m1) * (240 - hue) / 60;
+      else
+        b = m1;
+      
+      *h = r;
+      *l = g;
+      *s = b;
+    }
+}
+
+static void
+_shade_color (GdkRGBA *color,
+              gdouble  factor)
+{
+  GdkRGBA temp;
+
+  temp = *color;
+  rgb_to_hls (&temp.red, &temp.green, &temp.blue);
+
+  temp.green *= factor;
+  if (temp.green > 1.0)
+    temp.green = 1.0;
+  else if (temp.green < 0.0)
+    temp.green = 0.0;
+
+  temp.blue *= factor;
+  if (temp.blue > 1.0)
+    temp.blue = 1.0;
+  else if (temp.blue < 0.0)
+    temp.blue = 0.0;
+
+  hls_to_rgb (&temp.red, &temp.green, &temp.blue);
+  *color = temp;
+}
+
 /**
  * gtk_symbolic_color_resolve:
  * @color: a #GtkSymbolicColor
@@ -341,10 +516,8 @@ gtk_symbolic_color_resolve (GtkSymbolicColor   *color,
         if (!gtk_symbolic_color_resolve (color->shade.color, props, &shade))
           return FALSE;
 
-        resolved_color->red = CLAMP (shade.red * color->shade.factor, 0, 1);
-        resolved_color->green = CLAMP (shade.green * color->shade.factor, 0, 1);
-        resolved_color->blue = CLAMP (shade.blue * color->shade.factor, 0, 1);
-        resolved_color->alpha = shade.alpha;
+        _shade_color (&shade, color->shade.factor);
+        *resolved_color = shade;
 
         return TRUE;
       }