Use signals to detect DPI change

zathura/callbacks.c

@@ -216,6 +216,44 @@ cb_refresh_view(GtkWidget* GIRARA_UNUSED(view), gpointer data)
   statusbar_page_number_update(zathura);
 }
 
+void
+cb_monitors_changed(GdkScreen* screen, gpointer data)
+{
+  girara_debug("signal received");
+
+  zathura_t* zathura = data;
+  if (screen == NULL || zathura == NULL) {
+    return;
+  }
+
+  zathura_update_view_dpi(zathura);
+}
+
+void
+cb_widget_screen_changed(GtkWidget* widget, GdkScreen* UNUSED(previous_screen), gpointer data)
+{
+  girara_debug("signal received");
+
+  zathura_t* zathura = data;
+  if (widget == NULL || zathura == NULL) {
+    return;
+  }
+
+  if (gtk_widget_has_screen(widget)) {
+    GdkScreen* screen = gtk_widget_get_screen(widget);
+
+    /* disconnect signal on previous screen */
+    g_signal_handlers_disconnect_matched(screen, G_SIGNAL_MATCH_FUNC, 0, 0,
+        NULL, (gpointer) cb_monitors_changed, zathura);
+
+    /* connect to new screen */
+    g_signal_connect(G_OBJECT(screen),
+        "monitors-changed", G_CALLBACK(cb_monitors_changed), zathura);
+  }
+
+  zathura_update_view_dpi(zathura);
+}
+
 void
 cb_scale_factor(GObject* object, GParamSpec* UNUSED(pspec), gpointer data)
 {
@@ -235,6 +273,7 @@ cb_scale_factor(GObject* object, GParamSpec* UNUSED(pspec), gpointer data)
       fabs(new_factor - current.y) >= DBL_EPSILON) {
     zathura_document_set_device_factors(zathura->document, new_factor, new_factor);
     girara_debug("New device scale factor: %d", new_factor);
+    zathura_update_view_dpi(zathura);
     render_all(zathura);
   }
 }

zathura/callbacks.h

@@ -79,6 +79,30 @@ void cb_view_vadjustment_changed(GtkAdjustment *adjustment, gpointer data);
  */
 void cb_refresh_view(GtkWidget* view, gpointer data);
 
+/**
+ * This function gets called when the monitors associated with the GdkScreen
+ * change.
+ *
+ * It udpates the stored value for the monitor DPI.
+ *
+ * @param screen The GDK screen
+ * @param gpointer The zathura instance
+ */
+void cb_monitors_changed(GdkScreen* screen, gpointer data);
+
+/**
+ * This function gets called when the screen associated with the view widget
+ * changes.
+ *
+ * It udpates updates the connection on the monitors-changed ignal and the
+ * stored value for the monitor DPI.
+ *
+ * @param widget The view widget
+ * @param previous_screen The widget's previous screen
+ * @param gpointer The zathura instance
+ */
+void cb_widget_screen_changed(GtkWidget* widget, GdkScreen* previous_screen, gpointer data);
+
 /**
  * This function gets called when the view widget scale factor changes (e.g.
  * when moving from a regular to a HiDPI screen).

zathura/zathura.c

@@ -217,6 +217,9 @@ init_ui(zathura_t* zathura)
   g_signal_connect(G_OBJECT(zathura->ui.session->gtk.view),
       "notify::scale-factor", G_CALLBACK(cb_scale_factor), zathura);
 
+  g_signal_connect(G_OBJECT(zathura->ui.session->gtk.view),
+      "screen-changed", G_CALLBACK(cb_widget_screen_changed), zathura);
+
   /* page view */
   zathura->ui.page_widget = gtk_grid_new();
   gtk_grid_set_row_homogeneous(GTK_GRID(zathura->ui.page_widget), TRUE);
@@ -1025,6 +1028,9 @@ document_open(zathura_t* zathura, const char* path, const char* uri, const char*
 
   zathura_update_view_dpi(zathura);
 
+  /* call screen-changed callback to connect monitors-changed signal on initial screen */
+  cb_widget_screen_changed(zathura->ui.session->gtk.view, NULL, zathura);
+
   /* get initial device scale */
   int device_factor = gtk_widget_get_scale_factor(zathura->ui.session->gtk.view);
   zathura_document_set_device_factors(zathura->document, device_factor, device_factor);