Remove flicker when reloading

doc/configuration/options.rst

@@ -142,6 +142,14 @@ General settings
    :type: Boolean
    :default: false
 
+.. describe:: smooth-reload
+
+   Defines if flickering will be removed when a file is reloaded on change.
+   This option might increase memory usage.
+
+   :type: Boolean
+   :default: true
+
 .. describe:: zoom-max
 
   Defines the maximum percentage that the zoom level can be

doc/man/zathurarc.5.rst

@@ -749,6 +749,13 @@ zathura
   * Value type: Boolean
   * Default value: false
 
+*smooth-reload*
+  Defines if flickering will be removed when a file is reloaded on change. This
+  option might increase memory usage.
+
+  * Value type: Boolean
+  * Default value: true
+
 *render-loading*
   Defines if the "Loading..." text should be displayed if a page is rendered.
 

zathura/callbacks.c

@@ -204,6 +204,15 @@ cb_refresh_view(GtkWidget* GIRARA_UNUSED(view), gpointer data)
     return;
   }
 
+  if (zathura->pages != NULL && zathura->pages[page_id] != NULL) {
+	  ZathuraPage* page_widget = ZATHURA_PAGE(zathura->pages[page_id]);
+	  if (page_widget != NULL) {
+		  if (zathura_page_widget_have_surface(page_widget)) {
+			  document_predecessor_free(zathura);
+		  }
+	  }
+  }
+
   GtkAdjustment* vadj = gtk_scrolled_window_get_vadjustment(GTK_SCROLLED_WINDOW(zathura->ui.session->gtk.view));
   GtkAdjustment* hadj = gtk_scrolled_window_get_hadjustment(GTK_SCROLLED_WINDOW(zathura->ui.session->gtk.view));
 

zathura/config.c

@@ -267,6 +267,8 @@ config_load_default(zathura_t* zathura)
   girara_setting_add(gsession, "highlight-transparency", &float_value, FLOAT,   false, _("Transparency for highlighting"), NULL, NULL);
   bool_value = true;
   girara_setting_add(gsession, "render-loading",         &bool_value,  BOOLEAN, false, _("Render 'Loading ...'"), NULL, NULL);
+  bool_value = true;
+  girara_setting_add(gsession, "smooth-reload",          &bool_value,  BOOLEAN, false, _("Smooth over flicker when reloading file"), NULL, NULL);
   girara_setting_add(gsession, "adjust-open",            "best-fit",   STRING,  false, _("Adjust to when opening file"), NULL, NULL);
   bool_value = false;
   girara_setting_add(gsession, "show-hidden",            &bool_value,  BOOLEAN, false, _("Show hidden files and directories"), NULL, NULL);

zathura/page-widget.c

@@ -522,7 +522,28 @@ zathura_page_widget_draw(GtkWidget* widget, cairo_t* cairo)
   const unsigned int page_height = gtk_widget_get_allocated_height(widget);
   const unsigned int page_width  = gtk_widget_get_allocated_width(widget);
 
-  if (priv->surface != NULL || priv->thumbnail != NULL) {
+  bool smooth_reload = true;
+  girara_setting_get(priv->zathura->ui.session, "smooth-reload", &smooth_reload);
+
+  bool surface_exists = priv->surface != NULL || priv->thumbnail != NULL;
+
+  if (priv->zathura->predecessor_document != NULL && priv->zathura->predecessor_pages != NULL
+		  && smooth_reload && !surface_exists) {
+	  unsigned int page_index = zathura_page_get_index(priv->page);
+
+	  if (page_index < zathura_document_get_number_of_pages(priv->zathura->predecessor_document)) {
+		  /* render real page */
+		  zathura_render_request(priv->render_request, g_get_real_time());
+
+		  girara_debug("using predecessor page for idx %d", page_index);
+		  document = priv->zathura->predecessor_document;
+		  page = ZATHURA_PAGE(priv->zathura->predecessor_pages[page_index]);
+		  priv = zathura_page_widget_get_instance_private(page);
+	  }
+	  surface_exists = priv->surface != NULL || priv->thumbnail != NULL;
+  }
+
+  if (surface_exists) {
     cairo_save(cairo);
 
     const unsigned int rotation = zathura_document_get_rotation(document);
@@ -634,6 +655,10 @@ zathura_page_widget_draw(GtkWidget* widget, cairo_t* cairo)
       );
     }
   } else {
+	if (smooth_reload) {
+		girara_debug("rendering loading screen, flicker might be happening");
+	}
+
     /* set background color */
     if (zathura_renderer_recolor_enabled(priv->zathura->sync.render_thread) == true) {
       GdkRGBA color;

zathura/zathura.c

@@ -1493,6 +1493,32 @@ save_fileinfo_to_db(zathura_t* zathura)
   g_free(file_info.first_page_column_list);
 }
 
+bool
+document_predecessor_free(zathura_t* zathura) {
+  if (zathura == NULL
+	  || (zathura->predecessor_document == NULL
+		  && zathura->predecessor_pages == NULL)) {
+    return false;
+  }
+
+  if (zathura->predecessor_pages != NULL) {
+	  for (unsigned int i = 0; i < zathura_document_get_number_of_pages(zathura->predecessor_document); i++) {
+		g_object_unref(zathura->predecessor_pages[i]);
+	  }
+	  free(zathura->predecessor_pages);
+	  zathura->predecessor_pages = NULL;
+	  girara_debug("freed predecessor pages");
+  }
+  if (zathura->predecessor_document != NULL) {
+	  /* remove document */
+	  zathura_document_free(zathura->predecessor_document);
+	  zathura->predecessor_document = NULL;
+	  girara_debug("freed predecessor document");
+  }
+
+  return true;
+}
+
 bool
 document_close(zathura_t* zathura, bool keep_monitor)
 {
@@ -1508,6 +1534,9 @@ document_close(zathura_t* zathura, bool keep_monitor)
     g_free(window_icon);
   }
 
+  bool smooth_reload = true;
+  girara_setting_get(zathura->ui.session, "smooth-reload", &smooth_reload);
+
   /* stop rendering */
   zathura_renderer_stop(zathura->sync.render_thread);
   g_clear_object(&zathura->window_icon_render_request);
@@ -1543,17 +1572,43 @@ document_close(zathura_t* zathura, bool keep_monitor)
   /* release render thread */
   g_clear_object(&zathura->sync.render_thread);
 
+  /* keep the current state to prevent flicker? */
+  bool override_predecessor = keep_monitor && smooth_reload;
+
+  if (override_predecessor) {
+	  /* do not override predecessor buffer with empty pages */
+	  unsigned int cur_page_num = zathura_document_get_current_page_number(zathura->document);
+	  ZathuraPage* cur_page = ZATHURA_PAGE(zathura->pages[cur_page_num]);
+	  if (!zathura_page_widget_have_surface(cur_page)) {
+		  override_predecessor = false;
+	  }
+  }
+
+  /* free predecessor buffer if we want to overwrite it or if we destroy the document for good */
+  if (override_predecessor || !keep_monitor || !smooth_reload) {
+	  document_predecessor_free(zathura);
+  }
+
   /* remove widgets */
   gtk_container_foreach(GTK_CONTAINER(zathura->ui.page_widget), remove_page_from_table, NULL);
-  for (unsigned int i = 0; i < zathura_document_get_number_of_pages(zathura->document); i++) {
-    g_object_unref(zathura->pages[i]);
-  }
-  free(zathura->pages);
-  zathura->pages = NULL;
 
-  /* remove document */
-  zathura_document_free(zathura->document);
-  zathura->document = NULL;
+  if (!override_predecessor) {
+	  for (unsigned int i = 0; i < zathura_document_get_number_of_pages(zathura->document); i++) {
+		g_object_unref(zathura->pages[i]);
+	  }
+	  free(zathura->pages);
+	  zathura->pages = NULL;
+
+	  /* remove document */
+	  zathura_document_free(zathura->document);
+	  zathura->document = NULL;
+  } else {
+	  girara_debug("preserving pages and document as predecessor");
+	  zathura->predecessor_pages = zathura->pages;
+	  zathura->pages = NULL;
+	  zathura->predecessor_document = zathura->document;
+	  zathura->document = NULL;
+  }
 
   /* remove index */
   if (zathura->ui.index != NULL) {

zathura/zathura.h

@@ -184,7 +184,9 @@ struct zathura_s
   } stdin_support;
 
   zathura_document_t* document; /**< The current document */
+  zathura_document_t* predecessor_document; /**< The document from before a reload */
   GtkWidget** pages; /**< The page widgets */
+  GtkWidget** predecessor_pages; /**< The page widgets from before a reload */
   zathura_database_t* database; /**< The database */
   ZathuraDbus* dbus; /**< D-Bus service */
   ZathuraRenderRequest* window_icon_render_request; /**< Render request for window icon */
@@ -360,6 +362,14 @@ void document_open_idle(zathura_t* zathura, const char* path,
  */
 bool document_save(zathura_t* zathura, const char* path, bool overwrite);
 
+/**
+ * Frees the "predecessor" buffers used for smooth-reload
+ *
+ * @param zathura The zathura session
+ * @return If no error occurred true, otherwise false, is returned.
+ */
+bool document_predecessor_free(zathura_t* zathura);
+
 /**
  * Closes the current opened document
  *