HiDPI: watch GtkWidget scale-factor property

The scale-factor property is more specific than the GDK configure event
and is the recommended way to watch for scale factor changes.

zathura/callbacks.c

@@ -216,11 +216,11 @@ cb_refresh_view(GtkWidget* GIRARA_UNUSED(view), gpointer data)
   statusbar_page_number_update(zathura);
 }
 
-gboolean
-cb_window_configure(GtkWidget* widget, GdkEventConfigure* UNUSED(configure), zathura_t* zathura)
+void
+cb_scale_factor(GtkWidget* widget, GParamSpec* UNUSED(pspec), zathura_t* zathura)
 {
   if (widget == NULL || zathura == NULL || zathura->document == NULL) {
-    return false;
+    return;
   }
 
   int new_factor = gtk_widget_get_scale_factor(widget);
@@ -230,12 +230,11 @@ cb_window_configure(GtkWidget* widget, GdkEventConfigure* UNUSED(configure), zat
   zathura_document_get_device_scale(zathura->document, &current_x, &current_y);
 
   if (new_factor != current_x || new_factor != current_y) {
-    zathura_document_set_device_scale(zathura->document, new_factor, new_factor);
+    zathura_document_set_device_scale(zathura->document, new_factor,
+        new_factor);
     girara_debug("New device scale: %d", new_factor);
     render_all(zathura);
   }
-
-  return false;
 }
 
 void

zathura/callbacks.h

@@ -80,19 +80,16 @@ void cb_view_vadjustment_changed(GtkAdjustment *adjustment, gpointer data);
 void cb_refresh_view(GtkWidget* view, gpointer data);
 
 /**
- * This function gets called when the main window is reconfigured, i.e. when
- * its size, position or stacking order has changed, or when the device scale
- * factor has changed (e.g. when moving from a regular to a HiDPI screen).
+ * This function gets called when the view widget scale factor changes (e.g.
+ * when moving from a regular to a HiDPI screen).
  *
- * It checks if the device scale factor has changed and if yes, records the new
- * value and triggers a re-rendering of the document.
+ * It records the new value and triggers a re-rendering of the document.
  *
- * @param widget The main window GtkWidget
- * @param configure The GDK configure event
+ * @param widget The view widget
+ * @param pspec The GParamSpec for the scale-factor property
  * @param zathura The zathura instance
  */
-gboolean cb_window_configure(GtkWidget* widget, GdkEventConfigure* configure,
-    zathura_t* zathura);
+void cb_scale_factor(GtkWidget* widget, GParamSpec *pspec, zathura_t* zathura);
 
 /**
  * This function gets called when the value of the "pages-per-row"

zathura/zathura.c

@@ -153,8 +153,8 @@ init_ui(zathura_t* zathura)
   g_signal_connect(G_OBJECT(zathura->ui.session->gtk.view), "refresh-view",
                    G_CALLBACK(cb_refresh_view), zathura);
 
-  g_signal_connect(G_OBJECT(zathura->ui.session->gtk.window), "configure-event",
-                   G_CALLBACK(cb_window_configure), zathura);
+  g_signal_connect(G_OBJECT(zathura->ui.session->gtk.view),
+      "notify::scale-factor", G_CALLBACK(cb_scale_factor), zathura);
 
   /* page view */
   zathura->ui.page_widget = gtk_grid_new();
@@ -959,6 +959,10 @@ document_open(zathura_t* zathura, const char* path, const char* uri, const char*
   const unsigned int view_height = (unsigned int)floor(gtk_adjustment_get_page_size(vadjustment));
   zathura_document_set_viewport_height(zathura->document, view_height);
 
+  /* get initial device scale */
+  int device_scale = gtk_widget_get_scale_factor(zathura->ui.session->gtk.view);
+  zathura_document_set_device_scale(zathura->document, device_scale, device_scale);
+
   /* create blank pages */
   zathura->pages = calloc(number_of_pages, sizeof(GtkWidget*));
   if (zathura->pages == NULL) {