[evince] sidebar-thumbnails: keep thumbnails already rendered

[Nelson Benítez León <nbenitez src gnome org>]

commit 121e4d99a59c0c0586a4962f18423139e568f9f7
Author: Nelson Benítez León <nbenitezl+gnome gmail com>
Date:   Sat Jun 3 15:56:04 2017 +0500

    sidebar-thumbnails: keep thumbnails already rendered
    
    Evince renders thumbnails on-the-fly as they get into the
    scrolling visible area, but at the same time it will remove
    them as they get out of the visible scrolling area, so when
    user scrolls back to same position he will notice thumbnails
    be recreated.
    
    In pro of a more icing user experience, let's adopt a mixed approach
    and keep the thumbnails that the user has already navigated, so
    when he scrolls back and forth in the same area no thumbnail
    re-generation will be visible. This also matches behaviour with
    other pdf readers.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=342110

 shell/ev-sidebar-thumbnails.c |   34 ++++++++++++----------------------
 1 files changed, 12 insertions(+), 22 deletions(-)
---
diff --git a/shell/ev-sidebar-thumbnails.c b/shell/ev-sidebar-thumbnails.c
index c22e92e..6876c40 100644
--- a/shell/ev-sidebar-thumbnails.c
+++ b/shell/ev-sidebar-thumbnails.c
@@ -416,16 +416,14 @@ ev_sidebar_thumbnails_get_loading_icon (EvSidebarThumbnails *sidebar_thumbnails,
 }
 
 static void
-clear_range (EvSidebarThumbnails *sidebar_thumbnails,
-            gint                 start_page,
-            gint                 end_page)
+cancel_running_jobs (EvSidebarThumbnails *sidebar_thumbnails,
+                    gint                 start_page,
+                    gint                 end_page)
 {
        EvSidebarThumbnailsPrivate *priv = sidebar_thumbnails->priv;
        GtkTreePath *path;
        GtkTreeIter iter;
        gboolean result;
-       gint prev_width = -1;
-       gint prev_height = -1;
 
        g_assert (start_page <= end_page);
 
@@ -434,36 +432,28 @@ clear_range (EvSidebarThumbnails *sidebar_thumbnails,
             result && start_page <= end_page;
             result = gtk_tree_model_iter_next (GTK_TREE_MODEL (priv->list_store), &iter), start_page ++) {
                EvJobThumbnail *job;
-               cairo_surface_t *loading_icon = NULL;
-               gint width, height;
+               gboolean thumbnail_set;
 
                gtk_tree_model_get (GTK_TREE_MODEL (priv->list_store),
                                    &iter,
                                    COLUMN_JOB, &job,
+                                   COLUMN_THUMBNAIL_SET, &thumbnail_set,
                                    -1);
 
+               if (thumbnail_set) {
+                       g_assert (job == NULL);
+                       continue;
+               }
+
                if (job) {
                        g_signal_handlers_disconnect_by_func (job, thumbnail_job_completed_callback, 
sidebar_thumbnails);
                        ev_job_cancel (EV_JOB (job));
                        g_object_unref (job);
                }
 
-               ev_thumbnails_size_cache_get_size (priv->size_cache, start_page,
-                                                 priv->rotation,
-                                                 &width, &height);
-               if (!loading_icon || (width != prev_width && height != prev_height)) {
-                       loading_icon =
-                               ev_sidebar_thumbnails_get_loading_icon (sidebar_thumbnails,
-                                                                       width, height);
-               }
-
-               prev_width = width;
-               prev_height = height;
-
                gtk_list_store_set (priv->list_store, &iter,
                                    COLUMN_JOB, NULL,
                                    COLUMN_THUMBNAIL_SET, FALSE,
-                                   COLUMN_SURFACE, loading_icon,
                                    -1);
        }
        gtk_tree_path_free (path);
@@ -567,10 +557,10 @@ update_visible_range (EvSidebarThumbnails *sidebar_thumbnails,
 
        /* Clear the areas we no longer display */
        if (old_start_page >= 0 && old_start_page < start_page)
-               clear_range (sidebar_thumbnails, old_start_page, MIN (start_page - 1, old_end_page));
+               cancel_running_jobs (sidebar_thumbnails, old_start_page, MIN (start_page - 1, old_end_page));
        
        if (old_end_page > 0 && old_end_page > end_page)
-               clear_range (sidebar_thumbnails, MAX (end_page + 1, old_start_page), old_end_page);
+               cancel_running_jobs (sidebar_thumbnails, MAX (end_page + 1, old_start_page), old_end_page);
 
        add_range (sidebar_thumbnails, start_page, end_page);