[gtk+/rendering-cleanup-next] API: Add gtk_widget_get_transform_to_window()

[Benjamin Otte <otte src gnome org>]

commit 5ec429c864ca746211893865bebe2b3ba74bacc0
Author: Benjamin Otte <otte redhat com>
Date:   Wed Sep 22 16:10:45 2010 +0200

    API: Add gtk_widget_get_transform_to_window()
    
    The function reverses the transform that GTK does before emitting a draw
    event. So we can use it in "old" widgets to revert the coordinate system
    properly.

 docs/reference/gtk/gtk3-sections.txt |    1 +
 gtk/gtk.symbols                      |    1 +
 gtk/gtkwidget.c                      |   99 +++++++++++++++++++++++++---------
 gtk/gtkwidget.h                      |    3 +
 4 files changed, 79 insertions(+), 25 deletions(-)
---
diff --git a/docs/reference/gtk/gtk3-sections.txt b/docs/reference/gtk/gtk3-sections.txt
index 918bcd8..cfbac8a 100644
--- a/docs/reference/gtk/gtk3-sections.txt
+++ b/docs/reference/gtk/gtk3-sections.txt
@@ -4897,6 +4897,7 @@ gtk_widget_set_has_tooltip
 gtk_widget_trigger_tooltip_query
 gtk_widget_get_window
 gtk_cairo_should_draw_window
+gtk_widget_get_transform_to_window
 gtk_widget_get_allocated_width
 gtk_widget_get_allocated_height
 gtk_widget_get_allocation
diff --git a/gtk/gtk.symbols b/gtk/gtk.symbols
index 8039e0c..14ba8e1 100644
--- a/gtk/gtk.symbols
+++ b/gtk/gtk.symbols
@@ -4237,6 +4237,7 @@ gtk_widget_get_tooltip_markup
 gtk_widget_get_tooltip_text
 gtk_widget_get_tooltip_window
 gtk_widget_get_toplevel
+gtk_widget_get_transform_to_window
 gtk_widget_get_type G_GNUC_CONST
 gtk_widget_get_visible
 gtk_widget_get_visual
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 5afd974..e52239c 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -4519,6 +4519,70 @@ gtk_widget_translate_coordinates (GtkWidget  *src_widget,
   return TRUE;
 }
 
+/**
+ * gtk_widget_get_transform_to_window:
+ * @widget: the widget to translate from
+ * @window: the window to translate to
+ * @matrix: (out): location to take the return matrix.
+ *
+ * Computes the transformation to be applied for transforming the
+ * coordinate space of @widget to the coordinate space of @window.
+ * 
+ * Gtk applies the inverse of this function when preparing a
+ * #GdkExposeEvent to be emitted with GtkWidget::draw. So this
+ * function is useful to reverse this transformation and work in
+ * the @window's coordinate space as was the case with GTK 2.
+ *
+ * If the @widget's window is not an ancestor of @window, @matrix
+ * will be set to the identity matrix and %FALSE will be returned.
+ *
+ * Returns: %TRUE if a tranformation was set.
+ **/
+gboolean
+gtk_widget_get_transform_to_window (GtkWidget      *widget,
+                                    GdkWindow      *window,
+                                    cairo_matrix_t *matrix)
+{
+  GdkWindow *w, *widget_window;
+  int x, y;
+
+  g_return_val_if_fail (GTK_IS_WIDGET (widget), FALSE);
+  g_return_val_if_fail (GDK_IS_WINDOW (window), FALSE);
+  g_return_val_if_fail (matrix != NULL, FALSE);
+
+  if (!gtk_widget_get_has_window (widget))
+    {
+      x = -widget->priv->allocation.x;
+      y = -widget->priv->allocation.y;
+    }
+  else
+    {
+      x = 0;
+      y = 0;
+    }
+
+  widget_window = gtk_widget_get_window (widget);
+
+  for (w = window; w && w != widget_window; w = gdk_window_get_parent (w))
+    {
+      int wx, wy;
+      gdk_window_get_position (w, &wx, &wy);
+      x += wx;
+      y += wy;
+    }
+
+  if (w) 
+    {
+      cairo_matrix_init_translate (matrix, x, y);
+      return TRUE;
+    }
+  else
+    {
+      cairo_matrix_init_identity (matrix);
+      return FALSE;
+    }
+}
+
 static void
 gtk_widget_real_size_allocate (GtkWidget     *widget,
 			       GtkAllocation *allocation)
@@ -5266,10 +5330,10 @@ gint
 gtk_widget_send_expose (GtkWidget *widget,
 			GdkEvent  *event)
 {
-  GdkWindow *window, *w;
   gboolean result = FALSE;
+  cairo_matrix_t matrix;
   cairo_t *cr;
-  int x, y;
+  gboolean do_clip;
 
   g_return_val_if_fail (GTK_IS_WIDGET (widget), TRUE);
   g_return_val_if_fail (gtk_widget_get_realized (widget), TRUE);
@@ -5282,32 +5346,17 @@ gtk_widget_send_expose (GtkWidget *widget,
   gdk_cairo_region (cr, event->expose.region);
   cairo_clip (cr);
 
-  if (!gtk_widget_get_has_window (widget))
+  do_clip = gtk_widget_get_transform_to_window (widget,
+                                                event->expose.window,
+                                                &matrix);
+  /* matrix is just a translation so must be invertible */
+  if (cairo_matrix_invert (&matrix) != CAIRO_STATUS_SUCCESS)
     {
-      x = widget->priv->allocation.x;
-      y = widget->priv->allocation.y;
+      g_assert_not_reached ();
     }
-  else
-    {
-      x = 0;
-      y = 0;
-    }
-
-  /* translate cairo context properly */
-  window = gtk_widget_get_window (widget);
-
-  for (w = event->expose.window; w && w != window; w = gdk_window_get_parent (w))
-    {
-      int wx, wy;
-      gdk_window_get_position (w, &wx, &wy);
-      x -= wx;
-      y -= wy;
-    }
-
-  if (w)
-    cairo_translate (cr, x, y);
+  cairo_transform (cr, &matrix);
 
-  _gtk_widget_draw_internal (widget, cr, w != NULL);
+  _gtk_widget_draw_internal (widget, cr, do_clip);
 
   /* unset here, so if someone keeps a reference to cr we
    * don't leak the window. */
diff --git a/gtk/gtkwidget.h b/gtk/gtkwidget.h
index d154985..cb326df 100644
--- a/gtk/gtkwidget.h
+++ b/gtk/gtkwidget.h
@@ -807,6 +807,9 @@ gboolean     gtk_widget_translate_coordinates (GtkWidget  *src_widget,
 					       gint        src_y,
 					       gint       *dest_x,
 					       gint       *dest_y);
+gboolean     gtk_widget_get_transform_to_window (GtkWidget      *widget,
+                                                 GdkWindow      *window,
+                                                 cairo_matrix_t *matrix);
 
 /* Hide widget and return TRUE.
  */