[gnome-photos] image-view: Implement double-buffering

[Debarshi Ray <debarshir src gnome org>]

commit 5e4bbe9a0e444bc28f182a0ce9591c48298b09bb
Author: Debarshi Ray <debarshir gnome org>
Date:   Tue Jan 17 10:37:44 2017 +0100

    image-view: Implement double-buffering
    
    There are drawbacks to directly blitting the GeglNode that was passed
    to PhotosImageView.
    
    GEGL processes the graph in smaller chunks. The GeglNode might not be
    fully processed when we need to draw the widget, leading to rendering
    artifacts. We made this bearable in commit
    d2f4589f7747265786aed0da4046235f63f8e8d4 by not queuing a draw after
    each chunk is computed. However, the problem was still there. A draw
    may be queued for reasons completely beyond control. eg., the widget
    can get resized.
    
    Secondly, the zoom and positioning of the image were being updated for
    every chunk. It is wasteful. More importantly, due to the chunked
    processing, the output of the GeglNode might not be ready to match the
    latest value of the bounding box.
    
    Therefore, a separate graph, with a single gegl:buffer-source, is used
    for rendering. The output of the GeglNode is copied to a new
    GeglBuffer and fed into this graph. Changes to the GeglNode's bounding
    box, caused by modifications to its graph's connectivity or
    properties, are tracked, and so is the amount of area
    that has been computed. We update our GeglBuffer, zoom and positioning
    only when the entire bounding box has been computed.

 src/photos-image-view.c |  130 +++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 127 insertions(+), 3 deletions(-)
---
diff --git a/src/photos-image-view.c b/src/photos-image-view.c
index e7b8363..2629ade 100644
--- a/src/photos-image-view.c
+++ b/src/photos-image-view.c
@@ -21,18 +21,24 @@
 #include "config.h"
 
 #include <babl/babl.h>
+#include <cairo.h>
 #include <cairo-gobject.h>
 #include <glib.h>
 
 #include "photos-debug.h"
 #include "photos-image-view.h"
 #include "photos-marshalers.h"
+#include "photos-utils.h"
 
 
 struct _PhotosImageView
 {
   GtkDrawingArea parent_instance;
+  GeglNode *buffer_source;
+  GeglNode *graph;
   GeglNode *node;
+  cairo_region_t *bbox_region;
+  cairo_region_t *region;
   gfloat x;
   gfloat x_scaled;
   gfloat y;
@@ -63,6 +69,63 @@ static guint signals[LAST_SIGNAL] = { 0 };
 G_DEFINE_TYPE (PhotosImageView, photos_image_view, GTK_TYPE_DRAWING_AREA);
 
 
+static void photos_image_view_computed (PhotosImageView *self, GeglRectangle *rect);
+
+
+static void
+photos_image_view_update_graph (PhotosImageView *self)
+{
+  const Babl *format;
+  GeglBuffer *buffer = NULL;
+  gint64 end;
+  gint64 start;
+
+  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_signal_handlers_unblock_by_func (self->node, photos_image_view_computed, self);
+  g_object_unref (buffer);
+}
+
+
+static void
+photos_image_view_update_region (PhotosImageView *self)
+{
+  GeglRectangle bbox;
+
+  g_clear_pointer (&self->bbox_region, (GDestroyNotify) cairo_region_destroy);
+  g_clear_pointer (&self->region, (GDestroyNotify) cairo_region_destroy);
+
+  bbox = gegl_node_get_bounding_box (self->node);
+  self->bbox_region = cairo_region_create_rectangle ((cairo_rectangle_int_t *) &bbox);
+  self->region = cairo_region_create ();
+
+  photos_debug (PHOTOS_DEBUG_GEGL,
+                "PhotosImageView: Node (%p) Region: %d, %d, %d×%d",
+                self->node,
+                bbox.x,
+                bbox.y,
+                bbox.width,
+                bbox.height);
+}
+
+
 static void
 photos_image_view_update (PhotosImageView *self)
 {
@@ -76,12 +139,14 @@ photos_image_view_update (PhotosImageView *self)
   if (self->node == NULL)
     return;
 
+  g_return_if_fail (GEGL_IS_NODE (self->buffer_source));
+
   gtk_widget_get_allocation (GTK_WIDGET (self), &viewport);
 
   if (viewport.width < 0 || viewport.height < 0)
     return;
 
-  bbox = gegl_node_get_bounding_box (self->node);
+  bbox = gegl_node_get_bounding_box (self->buffer_source);
   if (bbox.width < 0 || bbox.height < 0)
     return;
 
@@ -118,6 +183,13 @@ photos_image_view_update (PhotosImageView *self)
 static void
 photos_image_view_computed (PhotosImageView *self, GeglRectangle *rect)
 {
+  cairo_status_t status;
+
+  g_return_if_fail (GEGL_IS_NODE (self->buffer_source));
+  g_return_if_fail (GEGL_IS_NODE (self->graph));
+  g_return_if_fail (self->bbox_region != NULL);
+  g_return_if_fail (self->region != NULL);
+
   photos_debug (PHOTOS_DEBUG_GEGL,
                 "PhotosImageView: Node (%p) Computed: %d, %d, %d×%d",
                 self->node,
@@ -126,11 +198,31 @@ photos_image_view_computed (PhotosImageView *self, GeglRectangle *rect)
                 rect->width,
                 rect->height);
 
+  status = cairo_region_union_rectangle (self->region, (cairo_rectangle_int_t *) rect);
+  g_return_if_fail (status == CAIRO_STATUS_SUCCESS);
+
+  if (!cairo_region_equal (self->bbox_region, self->region))
+    return;
+
+  photos_debug (PHOTOS_DEBUG_GEGL, "PhotosImageView: Node (%p) Computing Completed", self->node);
+
+  photos_image_view_update_graph (self);
   photos_image_view_update (self);
 }
 
 
 static void
+photos_image_view_invalidated (PhotosImageView *self)
+{
+  g_return_if_fail (PHOTOS_IS_IMAGE_VIEW (self));
+  g_return_if_fail (GEGL_IS_NODE (self->node));
+
+  photos_debug (PHOTOS_DEBUG_GEGL, "PhotosImageView: Node (%p) Invalidated", self->node);
+  photos_image_view_update_region (self);
+}
+
+
+static void
 photos_image_view_draw_node (PhotosImageView *self, cairo_t *cr, GdkRectangle *rect)
 {
   const Babl *format;
@@ -142,6 +234,8 @@ photos_image_view_draw_node (PhotosImageView *self, cairo_t *cr, GdkRectangle *r
   gint64 end;
   gint64 start;
 
+  g_return_if_fail (GEGL_IS_NODE (self->buffer_source));
+
   scale_factor = gtk_widget_get_scale_factor (GTK_WIDGET (self));
 
   roi.x = (gint) self->x_scaled + rect->x * scale_factor;
@@ -155,7 +249,7 @@ photos_image_view_draw_node (PhotosImageView *self, cairo_t *cr, GdkRectangle *r
 
   start = g_get_monotonic_time ();
 
-  gegl_node_blit (self->node,
+  gegl_node_blit (self->buffer_source,
                   (gdouble) self->zoom_scaled,
                   &roi,
                   format,
@@ -221,6 +315,7 @@ photos_image_view_dispose (GObject *object)
 {
   PhotosImageView *self = PHOTOS_IMAGE_VIEW (object);
 
+  g_clear_object (&self->graph);
   g_clear_object (&self->node);
 
   G_OBJECT_CLASS (photos_image_view_parent_class)->dispose (object);
@@ -228,6 +323,18 @@ photos_image_view_dispose (GObject *object)
 
 
 static void
+photos_image_view_finalize (GObject *object)
+{
+  PhotosImageView *self = PHOTOS_IMAGE_VIEW (object);
+
+  g_clear_pointer (&self->bbox_region, (GDestroyNotify) cairo_region_destroy);
+  g_clear_pointer (&self->region, (GDestroyNotify) cairo_region_destroy);
+
+  G_OBJECT_CLASS (photos_image_view_parent_class)->finalize (object);
+}
+
+
+static void
 photos_image_view_get_property (GObject *object, guint prop_id, GValue *value, GParamSpec *pspec)
 {
   PhotosImageView *self = PHOTOS_IMAGE_VIEW (object);
@@ -303,6 +410,7 @@ photos_image_view_class_init (PhotosImageViewClass *class)
   GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
 
   object_class->dispose = photos_image_view_dispose;
+  object_class->finalize = photos_image_view_finalize;
   object_class->get_property = photos_image_view_get_property;
   object_class->set_property = photos_image_view_set_property;
   widget_class->draw = photos_image_view_draw;
@@ -428,14 +536,30 @@ photos_image_view_set_node (PhotosImageView *self, GeglNode *node)
     return;
 
   if (self->node != NULL)
-    g_signal_handlers_disconnect_by_func (self->node, photos_image_view_computed, self);
+    {
+      g_signal_handlers_disconnect_by_func (self->node, photos_image_view_computed, self);
+      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->node);
+  g_clear_pointer (&self->bbox_region, (GDestroyNotify) cairo_region_destroy);
+  g_clear_pointer (&self->region, (GDestroyNotify) cairo_region_destroy);
 
   if (node != NULL)
     {
       self->node = g_object_ref (node);
+
+      photos_image_view_update_region (self);
+      photos_image_view_update_graph (self);
+
       g_signal_connect_object (node, "computed", G_CALLBACK (photos_image_view_computed), self, 
G_CONNECT_SWAPPED);
+      g_signal_connect_object (node,
+                               "invalidated",
+                               G_CALLBACK (photos_image_view_invalidated),
+                               self,
+                               G_CONNECT_SWAPPED);
     }
 
   photos_image_view_update (self);