gtk-demo: Add a simple example for theming

demos/gtk-demo/Makefile.am

@@ -15,6 +15,7 @@ demos =						\
 	clipboard.c				\
 	colorsel.c				\
 	combobox.c				\
+	css_basics.c				\
 	dialog.c				\
 	drawingarea.c				\
 	editable_cells.c			\

demos/gtk-demo/css_basics.c

@@ -0,0 +1,133 @@
+/* CSS Theming/CSS Basics
+ *
+ * Gtk themes are written using CSS. Every widget is build of multiple items
+ * that you can style very similarly to a regular website.
+ *
+ */
+
+#include <gtk/gtk.h>
+
+static GtkWidget *window = NULL;
+
+#define DEFAULT_CSS \
+  "/* You can edit the CSS to change the appearance of this Window */\n" \
+  "\n" \
+  "GtkWindow {\n" \
+  "  engine: none;\n" \
+  "  background-image: none;\n" \
+  "  background-color: brown;\n" \
+  "}\n" \
+  "\n" \
+  "GtkTextView {\n" \
+  "  color: green;\n" \
+  "}\n" \
+  "\n"
+
+static void
+show_parsing_error (GtkCssProvider *provider,
+                    GtkCssSection  *section,
+                    const GError   *error,
+                    GtkTextBuffer  *buffer)
+{
+  GtkTextIter start, end;
+  const char *tag_name;
+
+  gtk_text_buffer_get_iter_at_line_index (buffer,
+                                          &start,
+                                          gtk_css_section_get_start_line (section),
+                                          gtk_css_section_get_start_position (section));
+  gtk_text_buffer_get_iter_at_line_index (buffer,
+                                          &end,
+                                          gtk_css_section_get_end_line (section),
+                                          gtk_css_section_get_end_position (section));
+
+  if (g_error_matches (error, GTK_CSS_PROVIDER_ERROR, GTK_CSS_PROVIDER_ERROR_DEPRECATED))
+    tag_name = "warning";
+  else
+    tag_name = "error";
+
+  gtk_text_buffer_apply_tag_by_name (buffer, tag_name, &start, &end);
+}
+                    
+static void
+css_text_changed (GtkTextBuffer  *buffer,
+                  GtkCssProvider *provider)
+{
+  GtkTextIter start, end;
+  char *text;
+
+  gtk_text_buffer_get_start_iter (buffer, &start);
+  gtk_text_buffer_get_end_iter (buffer, &end);
+  gtk_text_buffer_remove_all_tags (buffer, &start, &end);
+
+  text = gtk_text_buffer_get_text (buffer, &start, &end, FALSE);
+  gtk_css_provider_load_from_data (provider, text, -1, NULL);
+  g_free (text);
+
+  gtk_style_context_reset_widgets (gdk_screen_get_default ());
+}
+
+static void
+apply_css (GtkWidget *widget, GtkStyleProvider *provider)
+{
+  gtk_style_context_add_provider (gtk_widget_get_style_context (widget), provider, G_MAXUINT);
+  if (GTK_IS_CONTAINER (widget))
+    gtk_container_forall (GTK_CONTAINER (widget), (GtkCallback) apply_css, provider);
+}
+
+GtkWidget *
+do_css_basics (GtkWidget *do_widget)
+{
+  if (!window)
+    {
+      GtkWidget *container, *child;
+      GtkStyleProvider *provider;
+      GtkTextBuffer *text;
+      
+      window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
+      gtk_window_set_transient_for (GTK_WINDOW (window), GTK_WINDOW (do_widget));
+      gtk_window_set_default_size (GTK_WINDOW (window), 400, 300);
+      g_signal_connect (window, "destroy",
+                        G_CALLBACK (gtk_widget_destroyed), &window);
+
+      text = gtk_text_buffer_new (NULL);
+      gtk_text_buffer_create_tag (text,
+                                  "warning",
+                                  "underline", PANGO_UNDERLINE_SINGLE,
+                                  NULL);
+      gtk_text_buffer_create_tag (text,
+                                  "error",
+                                  "underline", PANGO_UNDERLINE_ERROR,
+                                  NULL);
+
+      provider = GTK_STYLE_PROVIDER (gtk_css_provider_new ());
+      
+      container = gtk_scrolled_window_new (NULL, NULL);
+      gtk_container_add (GTK_CONTAINER (window), container);
+      child = gtk_text_view_new_with_buffer (text);
+      gtk_container_add (GTK_CONTAINER (container), child);
+      g_signal_connect (text,
+                        "changed",
+                        G_CALLBACK (css_text_changed),
+                        provider);
+      gtk_text_buffer_set_text (text,
+                                DEFAULT_CSS,
+                                -1);
+      g_signal_connect (provider,
+                        "parsing-error",
+                        G_CALLBACK (show_parsing_error),
+                        gtk_text_view_get_buffer (GTK_TEXT_VIEW (child)));
+
+      apply_css (window, provider);
+    }
+
+  if (!gtk_widget_get_visible (window))
+    gtk_widget_show_all (window);
+  else
+    {
+      gtk_widget_destroy (window);
+      window = NULL;
+    }
+
+  return window;
+}