[gtk/wip/baedert/for-master] widget: Avoid doing GtkSnapshot work just to append one node

[Timm Bäder <baedert src gnome org>]

commit 05c16e1e8367a8f6b61bea08f9c0d782d921823b
Author: Timm Bäder <mail baedert org>
Date:   Sat Jun 6 12:09:10 2020 +0200

    widget: Avoid doing GtkSnapshot work just to append one node
    
    We already know that a widget will have literally 1 node, not more.
    Avoid doing the GtkSnapshot state stack dance and just append a new
    transform node instead.
    
    Seems to give me around 400 more icons in the fishbowl

 gtk/gtkwidget.c | 60 +++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 37 insertions(+), 23 deletions(-)
---
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 91ad52e502..b840726959 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -11624,38 +11624,48 @@ gtk_widget_create_render_node (GtkWidget   *widget,
   return gtk_snapshot_pop_collect (snapshot);
 }
 
-void
-gtk_widget_snapshot (GtkWidget   *widget,
-                     GtkSnapshot *snapshot)
+static void
+gtk_widget_do_snapshot (GtkWidget *widget,
+                        GtkSnapshot *snapshot)
 {
   GtkWidgetPrivate *priv = gtk_widget_get_instance_private (widget);
+  GskRenderNode *render_node;
 
-  if (!_gtk_widget_get_mapped (widget))
+  if (!priv->draw_needed)
     return;
 
+  g_assert (priv->mapped);
+
   if (_gtk_widget_get_alloc_needed (widget))
     {
       g_warning ("Trying to snapshot %s %p without a current allocation", gtk_widget_get_name (widget), 
widget);
       return;
     }
 
-  if (priv->draw_needed)
-    {
-      GskRenderNode *render_node;
+  gtk_widget_push_paintables (widget);
 
-      gtk_widget_push_paintables (widget);
+  render_node = gtk_widget_create_render_node (widget, snapshot);
+  /* This can happen when nested drawing happens and a widget contains itself
+   * or when we replace a clipped area */
+  g_clear_pointer (&priv->render_node, gsk_render_node_unref);
+  priv->render_node = render_node;
 
-      render_node = gtk_widget_create_render_node (widget, snapshot);
-      /* This can happen when nested drawing happens and a widget contains itself
-       * or when we replace a clipped area */
-      g_clear_pointer (&priv->render_node, gsk_render_node_unref);
-      priv->render_node = render_node;
+  priv->draw_needed = FALSE;
 
-      priv->draw_needed = FALSE;
+  gtk_widget_pop_paintables (widget);
+  gtk_widget_update_paintables (widget);
+}
 
-      gtk_widget_pop_paintables (widget);
-      gtk_widget_update_paintables (widget);
-    }
+void
+gtk_widget_snapshot (GtkWidget   *widget,
+                     GtkSnapshot *snapshot)
+{
+  GtkWidgetPrivate *priv = gtk_widget_get_instance_private (widget);
+
+  if (!_gtk_widget_get_mapped (widget))
+    return;
+
+  gtk_widget_do_snapshot (widget, snapshot);
 
   if (priv->render_node)
     gtk_snapshot_append_node (snapshot, priv->render_node);
@@ -12041,18 +12051,22 @@ gtk_widget_snapshot_child (GtkWidget   *widget,
   if (!_gtk_widget_get_mapped (child))
     return;
 
+  gtk_widget_do_snapshot (child, snapshot);
+
+  if (!priv->render_node)
+    return;
+
   if (priv->transform)
     {
-      gtk_snapshot_save (snapshot);
-      gtk_snapshot_transform (snapshot, priv->transform);
-
-      gtk_widget_snapshot (child, snapshot);
+      GskRenderNode *transform_node = gsk_transform_node_new (priv->render_node,
+                                                              priv->transform);
 
-      gtk_snapshot_restore (snapshot);
+      gtk_snapshot_append_node (snapshot, transform_node);
+      gsk_render_node_unref (transform_node);
     }
   else
     {
-      gtk_widget_snapshot (child, snapshot);
+      gtk_snapshot_append_node (snapshot, priv->render_node);
     }
 }