diff --git a/ui/gtk.c b/ui/gtk.c
index 7ce73b0..93b13b7 100644
--- a/ui/gtk.c
+++ b/ui/gtk.c
@@ -891,7 +891,7 @@
     int x, y;
     int mx, my;
     int fbh, fbw;
-    int ww, wh, ws;
+    int ww, wh;
 
     if (!vc->gfx.ds) {
         return TRUE;
@@ -899,11 +899,15 @@
 
     fbw = surface_width(vc->gfx.ds) * vc->gfx.scale_x;
     fbh = surface_height(vc->gfx.ds) * vc->gfx.scale_y;
-
     ww = gtk_widget_get_allocated_width(widget);
     wh = gtk_widget_get_allocated_height(widget);
-    ws = gtk_widget_get_scale_factor(widget);
 
+    /*
+     * `widget` may not have the same size with the frame buffer.
+     * In such cases, some paddings are needed around the `vc`.
+     * To achieve that, `vc` will be displayed at (mx, my)
+     * so that it is displayed at the center of the widget.
+     */
     mx = my = 0;
     if (ww > fbw) {
         mx = (ww - fbw) / 2;
@@ -912,8 +916,12 @@
         my = (wh - fbh) / 2;
     }
 
-    x = (motion->x - mx) / vc->gfx.scale_x * ws;
-    y = (motion->y - my) / vc->gfx.scale_y * ws;
+    /*
+     * `motion` is reported in `widget` coordinates
+     * so translating it to the coordinates in `vc`.
+     */
+    x = (motion->x - mx) / vc->gfx.scale_x;
+    y = (motion->y - my) / vc->gfx.scale_y;
 
     trace_gd_motion_event(ww, wh, gtk_widget_get_scale_factor(widget), x, y);