[gnome-screenshot] screenshot-dialog: Avoid resizing the preview too much

[Rui Matos <rtcm src gnome org>]

commit c21823be42c12f2d17be23364137af0a5a10f6b3
Author: Rui Matos <tiagomatos gmail com>
Date:   Sun Jul 10 16:35:41 2016 +0200

    screenshot-dialog: Avoid resizing the preview too much
    
    Relying on configure events to resize the preview makes us do more
    work than necessary and, in particular, gtk+ sometimes sends us phony
    configure events sized 1x1 which make us hit a pretty CPU intensive
    resize operation in gdk-pixbuf.
    
    Instead, we can avoid all that by creating the preview pixbuf lazily
    on the draw handler using the actual allocated widget size.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=768087

 src/screenshot-dialog.c |   32 +++++++++++++++-----------------
 1 files changed, 15 insertions(+), 17 deletions(-)
---
diff --git a/src/screenshot-dialog.c b/src/screenshot-dialog.c
index fd0cbdc..b436df0 100644
--- a/src/screenshot-dialog.c
+++ b/src/screenshot-dialog.c
@@ -43,6 +43,21 @@ on_preview_draw (GtkWidget      *drawing_area,
 {
   ScreenshotDialog *dialog = data;
   GtkStyleContext *context;
+  int width, height;
+
+  width = gtk_widget_get_allocated_width (drawing_area);
+  height = gtk_widget_get_allocated_height (drawing_area);
+
+  if (!dialog->preview_image ||
+      gdk_pixbuf_get_width (dialog->preview_image) != width ||
+      gdk_pixbuf_get_height (dialog->preview_image) != height)
+    {
+      g_clear_object (&dialog->preview_image);
+      dialog->preview_image = gdk_pixbuf_scale_simple (dialog->screenshot,
+                                                       width,
+                                                       height,
+                                                       GDK_INTERP_BILINEAR);
+    }
 
   context = gtk_widget_get_style_context (drawing_area);
   gtk_style_context_save (context);
@@ -80,22 +95,6 @@ on_preview_button_release_event (GtkWidget      *drawing_area,
 }
 
 static void
-on_preview_configure_event (GtkWidget         *drawing_area,
-                           GdkEventConfigure *event,
-                           gpointer           data)
-{
-  ScreenshotDialog *dialog = data;
-
-  if (dialog->preview_image)
-    g_object_unref (G_OBJECT (dialog->preview_image));
-
-  dialog->preview_image = gdk_pixbuf_scale_simple (dialog->screenshot,
-                                                  event->width,
-                                                  event->height,
-                                                  GDK_INTERP_BILINEAR);
-}
-
-static void
 drag_data_get (GtkWidget          *widget,
               GdkDragContext     *context,
               GtkSelectionData   *selection_data,
@@ -179,7 +178,6 @@ setup_drawing_area (ScreenshotDialog *dialog, GtkBuilder *ui)
   g_signal_connect (preview_darea, "draw", G_CALLBACK (on_preview_draw), dialog);
   g_signal_connect (preview_darea, "button_press_event", G_CALLBACK (on_preview_button_press_event), dialog);
   g_signal_connect (preview_darea, "button_release_event", G_CALLBACK (on_preview_button_release_event), 
dialog);
-  g_signal_connect (preview_darea, "configure_event", G_CALLBACK (on_preview_configure_event), dialog);
 
   /* setup dnd */
   gtk_drag_source_set (preview_darea,