[gnome-photos/wip/rishi/double-buffering: 12/12] image-view: Don't use a gegl:buffer-source for double-buffering

[Debarshi Ray <debarshir src gnome org>]

commit f0eed8c0268232bcb4d3ee1f8e595f4537707df8
Author: Debarshi Ray <debarshir gnome org>
Date:   Tue Jan 17 13:37:51 2017 +0100

    image-view: Don't use a gegl:buffer-source for double-buffering
    
    Instead of using a GEGL graph with a gegl:buffer-source in it, we can
    directly use the GeglBuffer that we copied out of the GeglNode.
    Sometimes, it does take a few fractions of a second to process the
    gegl:buffer-source before it can be used. Probably due to overheads
    inherent to processing a GEGL graph. By directly using the GeglBuffer
    we can save that time.
    
    It is not clear if this is going to have any negative side-effects, or
    whether the time that we saved is going to show up elsewhere. That is
    why this has been done as a separate commit. We can always go back to
    using a gegl:buffer-source if things don't work out.

 src/photos-image-view.c |   59 +++++++++++++++++-----------------------------
 1 files changed, 22 insertions(+), 37 deletions(-)
---
diff --git a/src/photos-image-view.c b/src/photos-image-view.c
index ad4aa78..0922b86 100644
--- a/src/photos-image-view.c
+++ b/src/photos-image-view.c
@@ -34,8 +34,7 @@
 struct _PhotosImageView
 {
   GtkDrawingArea parent_instance;
-  GeglNode *buffer_source;
-  GeglNode *graph;
+  GeglBuffer *buffer;
   GeglNode *node;
   cairo_region_t *bbox_region;
   cairo_region_t *region;
@@ -73,31 +72,16 @@ static void photos_image_view_computed (PhotosImageView *self, GeglRectangle *re
 
 
 static void
-photos_image_view_update_graph (PhotosImageView *self)
+photos_image_view_update_buffer (PhotosImageView *self)
 {
   const Babl *format;
-  GeglBuffer *buffer = NULL;
-  gint64 end;
-  gint64 start;
+  GeglBuffer *buffer;
 
-  g_clear_object (&self->graph);
   g_signal_handlers_block_by_func (self->node, photos_image_view_computed, self);
 
   format = babl_format ("cairo-ARGB32");
   buffer = photos_utils_dup_buffer_from_node (self->node, format);
-
-  self->graph = gegl_node_new ();
-  self->buffer_source = gegl_node_new_child (self->graph,
-                                             "operation", "gegl:buffer-source",
-                                             "buffer", buffer,
-                                             NULL);
-
-  start = g_get_monotonic_time ();
-
-  gegl_node_process (self->buffer_source);
-
-  end = g_get_monotonic_time ();
-  photos_debug (PHOTOS_DEBUG_GEGL, "PhotosImageView: Process Buffer: %" G_GINT64_FORMAT, end - start);
+  g_set_object (&self->buffer, buffer);
 
   g_signal_handlers_unblock_by_func (self->node, photos_image_view_computed, self);
   g_object_unref (buffer);
@@ -139,14 +123,14 @@ photos_image_view_update (PhotosImageView *self)
   if (self->node == NULL)
     return;
 
-  g_return_if_fail (GEGL_IS_NODE (self->buffer_source));
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer));
 
   gtk_widget_get_allocation (GTK_WIDGET (self), &viewport);
 
   if (viewport.width < 0 || viewport.height < 0)
     return;
 
-  bbox = gegl_node_get_bounding_box (self->buffer_source);
+  bbox = *gegl_buffer_get_extent (self->buffer);
   if (bbox.width < 0 || bbox.height < 0)
     return;
 
@@ -186,9 +170,8 @@ photos_image_view_computed (PhotosImageView *self, GeglRectangle *rect)
   cairo_status_t status;
 
   g_return_if_fail (PHOTOS_IS_IMAGE_VIEW (self));
-  g_return_if_fail (GEGL_IS_NODE (self->buffer_source));
-  g_return_if_fail (GEGL_IS_NODE (self->graph));
   g_return_if_fail (GEGL_IS_NODE (self->node));
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer));
   g_return_if_fail (self->bbox_region != NULL);
   g_return_if_fail (self->region != NULL);
 
@@ -208,7 +191,7 @@ photos_image_view_computed (PhotosImageView *self, GeglRectangle *rect)
 
   photos_debug (PHOTOS_DEBUG_GEGL, "PhotosImageView: Node (%p) Computing Completed", self->node);
 
-  photos_image_view_update_graph (self);
+  photos_image_view_update_buffer (self);
   photos_image_view_update (self);
   gtk_widget_queue_draw (GTK_WIDGET (self));
 }
@@ -232,12 +215,13 @@ photos_image_view_draw_node (PhotosImageView *self, cairo_t *cr, GdkRectangle *r
   GeglRectangle roi;
   cairo_surface_t *surface = NULL;
   guchar *buf = NULL;
+  gint bpp;
   gint scale_factor;
   gint stride;
   gint64 end;
   gint64 start;
 
-  g_return_if_fail (GEGL_IS_NODE (self->buffer_source));
+  g_return_if_fail (GEGL_IS_BUFFER (self->buffer));
 
   scale_factor = gtk_widget_get_scale_factor (GTK_WIDGET (self));
 
@@ -252,13 +236,15 @@ photos_image_view_draw_node (PhotosImageView *self, cairo_t *cr, GdkRectangle *r
 
   start = g_get_monotonic_time ();
 
-  gegl_node_blit (self->buffer_source,
-                  (gdouble) self->zoom_scaled,
-                  &roi,
-                  format,
-                  buf,
-                  GEGL_AUTO_ROWSTRIDE,
-                  GEGL_BLIT_CACHE | GEGL_BLIT_DIRTY);
+  bpp = babl_format_get_bytes_per_pixel (format);
+  stride = bpp * roi.width;
+  gegl_buffer_get (self->buffer,
+                   &roi,
+                   (gdouble) self->zoom_scaled,
+                   format,
+                   buf,
+                   stride,
+                   GEGL_ABYSS_NONE);
 
   end = g_get_monotonic_time ();
   photos_debug (PHOTOS_DEBUG_GEGL, "PhotosImageView: Node Blit: %" G_GINT64_FORMAT, end - start);
@@ -318,7 +304,7 @@ photos_image_view_dispose (GObject *object)
 {
   PhotosImageView *self = PHOTOS_IMAGE_VIEW (object);
 
-  g_clear_object (&self->graph);
+  g_clear_object (&self->buffer);
   g_clear_object (&self->node);
 
   G_OBJECT_CLASS (photos_image_view_parent_class)->dispose (object);
@@ -544,8 +530,7 @@ photos_image_view_set_node (PhotosImageView *self, GeglNode *node)
       g_signal_handlers_disconnect_by_func (self->node, photos_image_view_invalidated, self);
     }
 
-  self->buffer_source = NULL;
-  g_clear_object (&self->graph);
+  g_clear_object (&self->buffer);
   g_clear_object (&self->node);
   g_clear_pointer (&self->bbox_region, (GDestroyNotify) cairo_region_destroy);
   g_clear_pointer (&self->region, (GDestroyNotify) cairo_region_destroy);
@@ -555,7 +540,7 @@ photos_image_view_set_node (PhotosImageView *self, GeglNode *node)
       self->node = g_object_ref (node);
 
       photos_image_view_update_region (self);
-      photos_image_view_update_graph (self);
+      photos_image_view_update_buffer (self);
 
       g_signal_connect_object (node, "computed", G_CALLBACK (photos_image_view_computed), self, 
G_CONNECT_SWAPPED);
       g_signal_connect_object (node,