[gtk] widget: Add optimizations to gtk_widget_compute_transform()

[Benjamin Otte <otte src gnome org>]

commit cfc7dc016e96cc504be1bbdb8f6b3aae96031dc3
Author: Benjamin Otte <otte redhat com>
Date:   Wed Feb 20 04:04:29 2019 +0100

    widget: Add optimizations to gtk_widget_compute_transform()
    
    Try to catch 2 common cases with as little work as necessary.

 gtk/gtkwidget.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 45c4818ae3..d4a8284ae4 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -11259,6 +11259,13 @@ gtk_widget_compute_transform (GtkWidget         *widget,
   g_return_val_if_fail (GTK_IS_WIDGET (target), FALSE);
   g_return_val_if_fail (out_transform != NULL, FALSE);
 
+  /* optimization for common case: parent wants coordinates of a direct child */
+  if (target == widget->priv->parent)
+    {
+      graphene_matrix_init_from_matrix (out_transform, &widget->priv->transform);
+      return TRUE;
+    }
+
   ancestor = gtk_widget_common_ancestor (widget, target);
   if (ancestor == NULL)
     return FALSE;
@@ -11271,6 +11278,13 @@ gtk_widget_compute_transform (GtkWidget         *widget,
       graphene_matrix_multiply (&transform, &priv->transform, &transform);
     }
 
+  /* optimization for common case: parent wants coordinates of a non-direct child */
+  if (ancestor == target)
+    {
+      graphene_matrix_init_from_matrix (out_transform, &transform);
+      return TRUE;
+    }
+
   graphene_matrix_init_identity (&inverse);
   for (iter = target; iter != ancestor; iter = iter->priv->parent)
     {