nemo-desktop: Allow adjustment to label shadow.

Add two settings:
- desktop-text-shadow: Three levels of shadow (normal, darker,
  darkest) - normal being the traditional amount.
- desktop-text-shadow-use-theme: If true, and if the theme supports
  it, allow the GTK theme to control desktop style, including text
  shadow.

Nemo has always checked for theme support at startup and during
theme changes, to ensure custom widgets/features worked correctly
for users (such as inactive-pane shading). We add another check for
'nemo-desktop' there. If the theme lacks any support, nemo provides
it like before, using the shadow-level setting.

Author: mtwebster

eel/eel-theme-utils.c

@@ -2,6 +2,7 @@
 #include "eel-string.h"
 
 static GtkCssProvider *mandatory_css_provider = NULL;
+static gboolean theme_has_desktop_support = FALSE;
 
 static gboolean
 css_provider_load_from_resource (GtkCssProvider *provider,
@@ -96,8 +97,6 @@ add_fallback_mandatory_css_provider (const gchar *theme_name)
         goto out;
     }
 
-    /* Our fallback uses @theme_ prefixed names for colors. If the active theme does also, skip
-     * to apply */
     if (g_strstr_len (css, -1, "theme_selected_bg_color")) {
         final_fallback_css = g_strdup (init_fallback_css);
 
@@ -126,6 +125,7 @@ add_fallback_mandatory_css_provider (const gchar *theme_name)
     if (error) {
         g_warning ("Failed to create a fallback provider: %s", error->message);
         g_clear_error (&error);
+        g_clear_object (&mandatory_css_provider);
         goto out;
     }
 
@@ -174,6 +174,20 @@ is_known_supported_theme (const gchar *theme_name)
     return ret;
 }
 
+static void
+check_desktop_support (const gchar *theme_name)
+{
+    GtkCssProvider *provider;
+    gchar *css;
+
+    provider = gtk_css_provider_get_named (theme_name, NULL);
+    css = gtk_css_provider_to_string (provider);
+
+    theme_has_desktop_support = (g_strstr_len (css, -1, "nemo-desktop") != NULL);
+
+    g_free (css);
+}
+
 static void
 process_theme (GtkSettings *gtk_settings)
 {
@@ -194,13 +208,28 @@ process_theme (GtkSettings *gtk_settings)
         add_fallback_mandatory_css_provider (theme_name);
     }
 
+    check_desktop_support (theme_name);
+
     gtk_style_context_reset_widgets (gdk_screen_get_default ());
     g_free (theme_name);
 }
 
+gboolean
+eel_theme_utils_theme_supports_desktop (void)
+{
+    return theme_has_desktop_support;
+}
+
 void
 eel_theme_utils_init_styles (void)
 {
+    static gboolean initialized = FALSE;
+
+    if (initialized)
+        return;
+
+    initialized = TRUE;
+
     add_css_provider_at_priority ("/org/nemo/nemo-style-fallback.css",
                                   GTK_STYLE_PROVIDER_PRIORITY_FALLBACK);
 

eel/eel-theme-utils.h

@@ -3,6 +3,7 @@
 
 #include <gtk/gtk.h>
 
-void     eel_theme_utils_init_styles    (void);
+void     eel_theme_utils_init_styles              (void);
+gboolean eel_theme_utils_theme_supports_desktop  (void);
 
 #endif /* EEL_THEME_UTILS_H */

gresources/nemo-desktop-preferences.glade

@@ -516,7 +516,7 @@
       <object class="GtkFrame">
         <property name="visible">True</property>
         <property name="can_focus">False</property>
-        <property name="margin_bottom">2</property>
+        <property name="margin_bottom">10</property>
         <property name="label_xalign">0</property>
         <property name="label_yalign">0</property>
         <property name="shadow_type">in</property>

gresources/nemo-style-application.css

@@ -23,24 +23,57 @@ NemoDesktopWindow GtkPaned {
     -NemoIconContainer-activate-prelight-icon-label: true;
 }
 
-.nemo-desktop.nemo-canvas-item {
+/* Shadow variant: Normal (traditional nemo default) */
+.nemo-desktop.nemo-canvas-item.shadow-normal {
     color: #eeeeee;
     text-shadow: 1px 1px alpha(black, 0.8);
 }
 
-.nemo-desktop.nemo-canvas-item:hover {
+/* Shadow variant: Darker */
+.nemo-desktop.nemo-canvas-item.shadow-darker {
+    color: #eeeeee;
+    text-shadow: 1px 1px black;
+}
+
+/* Shadow variant: Darkest */
+.nemo-desktop.nemo-canvas-item.shadow-darkest {
+    color: #eeeeee;
+    text-shadow: 1px 1px black, 1px 0px alpha(black, 0.6), 0px 1px alpha(black, 0.6);
+}
+
+/* Hover for shadow modes */
+.nemo-desktop.nemo-canvas-item.shadow-normal:hover,
+.nemo-desktop.nemo-canvas-item.shadow-darker:hover,
+.nemo-desktop.nemo-canvas-item.shadow-darkest:hover {
     background-color: alpha(black, 0.5);
     background-image: none;
     text-shadow: none;
 }
 
-.nemo-desktop.nemo-canvas-item:selected {
+/* Selected for shadow modes */
+.nemo-desktop.nemo-canvas-item.shadow-normal:selected,
+.nemo-desktop.nemo-canvas-item.shadow-darker:selected,
+.nemo-desktop.nemo-canvas-item.shadow-darkest:selected {
     background-color: alpha(@theme_selected_bg_color, 0.8);
     background-image: none;
     text-shadow: none;
     color: #f5f5f5;
 }
 
+/* "Use current theme" hover/selected — provide highlight feedback
+   without forcing text color or shadow. Lower specificity (2 classes)
+   than shadow variants above (3 classes), so only applies when no
+   shadow class is set. */
+.nemo-desktop.nemo-canvas-item:hover {
+    background-color: alpha(black, 0.5);
+    background-image: none;
+}
+
+.nemo-desktop.nemo-canvas-item:selected {
+    background-color: alpha(@theme_selected_bg_color, 0.8);
+    background-image: none;
+}
+
 /* EelEditableLabel (icon labels) */
 .nemo-desktop.view .entry,
 .nemo-desktop.view .entry:active,