widget: Add draw signal

For now, the draw signal is emitted by default from the expose event, so
widgets can chose to either implement the expose event or the draw
function.
This is for the transitional period from expose event to draw signal.

Note that for now subclasses can only implement the draw function when
none of their parents implemented the expose event.

gtk/gtkwidget.c

@@ -49,6 +49,7 @@
 #include "gdk/gdkprivate.h" /* Used in gtk_reset_shapes_recurse to avoid copy */
 #include <gobject/gvaluecollector.h>
 #include <gobject/gobjectnotifyqueue.c>
+#include <cairo-gobject.h>
 #include "gdk/gdkkeysyms.h"
 #include "gtkaccessible.h"
 #include "gtktooltip.h"
@@ -198,6 +199,7 @@ enum {
   DIRECTION_CHANGED,
   GRAB_NOTIFY,
   CHILD_NOTIFY,
+  DRAW,
   MNEMONIC_ACTIVATE,
   GRAB_FOCUS,
   FOCUS,
@@ -340,6 +342,8 @@ static gboolean gtk_widget_real_show_help        (GtkWidget         *widget,
 static void	gtk_widget_dispatch_child_properties_changed	(GtkWidget        *object,
 								 guint             n_pspecs,
 								 GParamSpec      **pspecs);
+static gboolean		gtk_widget_real_expose_event    	(GtkWidget        *widget,
+								 GdkEventExpose   *event);
 static gboolean		gtk_widget_real_key_press_event   	(GtkWidget        *widget,
 								 GdkEventKey      *event);
 static gboolean		gtk_widget_real_key_release_event 	(GtkWidget        *widget,
@@ -527,6 +531,32 @@ child_property_notify_dispatcher (GObject     *object,
   GTK_WIDGET_GET_CLASS (object)->dispatch_child_properties_changed (GTK_WIDGET (object), n_pspecs, pspecs);
 }
 
+/* We guard against the draw signal callbacks modifying the state of the
+ * cairo context by surounding it with save/restore.
+ * Maybe we should also cairo_new_path() just to be sure?
+ */
+static void
+gtk_widget_draw_marshaller (GClosure     *closure,
+                            GValue       *return_value,
+                            guint         n_param_values,
+                            const GValue *param_values,
+                            gpointer      invocation_hint,
+                            gpointer      marshal_data)
+{
+  cairo_t *cr = g_value_get_boxed (&param_values[1]);
+
+  cairo_save (cr);
+
+  _gtk_marshal_BOOLEAN__BOXED (closure,
+                               return_value,
+                               n_param_values,
+                               param_values,
+                               invocation_hint,
+                               marshal_data);
+
+  cairo_restore (cr);
+}
+
 static void
 gtk_widget_class_init (GtkWidgetClass *klass)
 {
@@ -589,6 +619,7 @@ gtk_widget_class_init (GtkWidgetClass *klass)
   klass->direction_changed = gtk_widget_real_direction_changed;
   klass->grab_notify = NULL;
   klass->child_notify = NULL;
+  klass->draw = NULL;
   klass->mnemonic_activate = gtk_widget_real_mnemonic_activate;
   klass->grab_focus = gtk_widget_real_grab_focus;
   klass->focus = gtk_widget_real_focus;
@@ -598,7 +629,7 @@ gtk_widget_class_init (GtkWidgetClass *klass)
   klass->motion_notify_event = NULL;
   klass->delete_event = NULL;
   klass->destroy_event = NULL;
-  klass->expose_event = NULL;
+  klass->expose_event = gtk_widget_real_expose_event;
   klass->key_press_event = gtk_widget_real_key_press_event;
   klass->key_release_event = gtk_widget_real_key_release_event;
   klass->enter_notify_event = NULL;
@@ -1249,6 +1280,32 @@ gtk_widget_class_init (GtkWidgetClass *klass)
 		   G_TYPE_NONE, 1,
 		   G_TYPE_PARAM);
 
+  /**
+   * GtkWidget::draw:
+   * @widget: the object which received the signal
+   * @cr: the cairo context to draw to
+   * @width: width of the widget
+   * @height: height of the widget
+   *
+   * This signal is emitted when a widget is supposed to render itself.
+   * The @widget's top left corner must be painted at the origin of
+   * the passed in context and be sized in the given @width and @height.
+   *
+   * Signal handlers connected to this signal can modify the cairo
+   * context passed as @cr in any way they like and don't need to
+   * restore it. The signal emission takes care of calling cairo_save()
+   * before and cairo_restore() after invoking the handler.
+   */
+  widget_signals[DRAW] =
+    g_signal_new (I_("draw"),
+		   G_TYPE_FROM_CLASS (gobject_class),
+		   G_SIGNAL_RUN_LAST,
+		   G_STRUCT_OFFSET (GtkWidgetClass, draw),
+                   _gtk_boolean_handled_accumulator, NULL,
+                   gtk_widget_draw_marshaller,
+		   G_TYPE_BOOLEAN, 1,
+		   CAIRO_GOBJECT_TYPE_CONTEXT);
+
   /**
    * GtkWidget::mnemonic-activate:
    * @widget: the object which received the signal.
@@ -5013,6 +5070,36 @@ gtk_widget_real_mnemonic_activate (GtkWidget *widget,
   return TRUE;
 }
 
+static gboolean
+gtk_widget_real_expose_event (GtkWidget      *widget,
+			      GdkEventExpose *expose)
+{
+  gboolean result = FALSE;
+  cairo_t *cr;
+
+  if (!gtk_widget_is_drawable (widget))
+    return FALSE;
+
+  cr = gdk_cairo_create (expose->window);
+  gdk_cairo_region (cr, expose->region);
+  cairo_clip (cr);
+
+  if (!gtk_widget_get_has_window (widget))
+    {
+      cairo_translate (cr,
+                       widget->priv->allocation.x,
+                       widget->priv->allocation.y);
+    }
+
+  g_signal_emit (widget, widget_signals[DRAW], 
+                 0, cr,
+                 &result);
+                
+  cairo_destroy (cr);
+
+  return result;
+}
+
 static gboolean
 gtk_widget_real_key_press_event (GtkWidget         *widget,
 				 GdkEventKey       *event)

gtk/gtkwidget.h

@@ -348,6 +348,8 @@ struct _GtkWidgetClass
 				gboolean          was_grabbed);
   void (* child_notify)        (GtkWidget	 *widget,
 				GParamSpec       *pspec);
+  gboolean (* draw)	       (GtkWidget	 *widget,
+                                cairo_t          *cr);
   
   /* Mnemonics */
   gboolean (* mnemonic_activate) (GtkWidget    *widget,
@@ -937,6 +939,9 @@ void       gtk_widget_set_has_tooltip       (GtkWidget   *widget,
 					     gboolean     has_tooltip);
 gboolean   gtk_widget_get_has_tooltip       (GtkWidget   *widget);
 
+gboolean   gtk_cairo_should_draw_window     (cairo_t     *cr,
+                                             GdkWindow   *window);
+
 GType           gtk_requisition_get_type (void) G_GNUC_CONST;
 GtkRequisition *gtk_requisition_new      (void) G_GNUC_MALLOC;
 GtkRequisition *gtk_requisition_copy     (const GtkRequisition *requisition);