diff --git a/solidify/overlap.c b/solidify/overlap.c
index c69bae4..2a66f3f 100644
--- a/solidify/overlap.c
+++ b/solidify/overlap.c
@@ -17,24 +17,34 @@
 #include <limits.h>
 #include <gtk/gtk.h>
 
+#include "util.h"
 #include "face.h"
 #include "solid.h"
+#include "style.h"
 #include "overlap.h"
 
 
 #define	UNDEF_F	HUGE_VAL
-#define BORDER 10	/* pixels around the minimum drawing area */
+
+
+static int has_osd;
 
 
 static int sx(const struct solid *s)
 {
-	return (s->a->sx > s->b->sx ? s->a->sx : s->b->sx)+2*BORDER;
+	return (s->a->sx > s->b->sx ? s->a->sx : s->b->sx)+2*OVERLAP_BORDER;
 }
 
 
 static int sy(const struct solid *s)
 {
-	return (s->a->sy > s->b->sy ? s->a->sy : s->b->sy)+2*BORDER;
+	return (s->a->sy > s->b->sy ? s->a->sy : s->b->sy)+2*OVERLAP_BORDER;
+}
+
+
+static double r_center(const struct solid *s)
+{
+	return hypot(sx(s), sy(s))/OVERLAP_CENTER_DIV;
 }
 
 
@@ -136,7 +146,7 @@ static void point(const struct solid *s, int x, int y, guchar *p)
 }
 
 
-static void draw_image(GtkWidget *widget, struct solid *s)
+static void draw_map(GtkWidget *widget, struct solid *s)
 {
 	guchar *rgbbuf, *p;
 	int x, y;
@@ -158,6 +168,23 @@ static void draw_image(GtkWidget *widget, struct solid *s)
 }
 
 
+static void draw_image(GtkWidget *widget, struct solid *s, int osd)
+{
+	int cx = sx(s)/2;
+	int cy = sy(s)/2;
+	int p;
+
+	draw_map(widget, s);
+	has_osd = osd;
+	if (!osd)
+		return;
+	draw_circle(widget->window, gc_osd, cx, cy, r_center(s));
+	p = r_center(s)/sqrt(2);
+	gdk_draw_line(widget->window, gc_osd, cx-p, cy-p, cx+p, cy+p);
+	gdk_draw_line(widget->window, gc_osd, cx-p, cy+p, cx+p, cy-p);
+}
+
+
 /*
  * Rotate such that a point at distance "r" moves one unit. Rotate
  * counter-clockwise for r > 1, clockwise for r < 0.
@@ -200,6 +227,21 @@ static void shift(struct matrix *m, int dx, int dy, int dir)
 }
 
 
+static int osd_proximity(const struct solid *s, int dx, int dy)
+{
+	double r = hypot(dx, dy);
+	double rc = r_center(s);
+
+	if (fabs(r-rc) < OSD_PROXIMITY)
+		return 1;
+	if (r > rc)
+		return 0;
+	if (abs(abs(dx)-abs(dy)) < OSD_PROXIMITY)
+		return 1;
+	return 0;
+}
+
+
 static gboolean scroll_event(GtkWidget *widget, GdkEventScroll *event,
     gpointer data)
 {
@@ -208,7 +250,9 @@ static gboolean scroll_event(GtkWidget *widget, GdkEventScroll *event,
 	int dx = event->x-sx(s)/2;
 	int dy = event->y-sy(s)/2;
 	double r = hypot(dx, dy);
-	int center = r/hypot(sx(s), sy(s)) < 0.25;
+	double rc = r_center(s);
+	int center = r < rc;
+	int osd = osd_proximity(s, dx, dy);
 
 	if (r < 1)
 		return TRUE;
@@ -217,15 +261,15 @@ static gboolean scroll_event(GtkWidget *widget, GdkEventScroll *event,
 		if (center)
 			shift(&s->a->m, dx, dy, 1);
 		else
-			rotate(&s->a->m, r);
-		draw_image(darea, s);
+			rotate(&s->a->m, -r);
+		draw_image(darea, s, osd);
 		break;
 	case GDK_SCROLL_DOWN:
 		if (center)
 			shift(&s->a->m, dx, dy, -1);
 		else
-			rotate(&s->a->m, -r);
-		draw_image(darea, s);
+			rotate(&s->a->m, r);
+		draw_image(darea, s, osd);
 		break;
 	default:
 		/* ignore */;
@@ -237,11 +281,24 @@ static gboolean scroll_event(GtkWidget *widget, GdkEventScroll *event,
 static gboolean expose_event(GtkWidget *widget, GdkEventExpose *event,
     gpointer user_data)
 {
-	draw_image(widget, user_data);
+	draw_image(widget, user_data, has_osd);
 	return TRUE;
 }
 
 
+static gboolean motion_notify_event(GtkWidget *widget, GdkEventMotion *event,
+    gpointer data)
+{
+	struct solid *s = data;
+	int dx = event->x-sx(s)/2;
+	int dy = event->y-sy(s)/2;
+	int osd = osd_proximity(s, dx, dy);
+
+	if (osd != has_osd)
+		draw_image(widget, s, osd);
+	return FALSE;
+}
+
 
 void overlap(GtkWidget *canvas, struct solid *s)
 {
@@ -249,14 +306,24 @@ void overlap(GtkWidget *canvas, struct solid *s)
 
 	evbox = gtk_event_box_new();
 	darea = gtk_drawing_area_new();
+
+	gtk_widget_set_events(darea,
+	    GDK_EXPOSE | GDK_KEY_PRESS_MASK |
+	    GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK |
+	    GDK_SCROLL |
+	    GDK_POINTER_MOTION_MASK);
+
 	gtk_widget_set_size_request(darea, sx(s), sy(s));
 	gtk_container_add(GTK_CONTAINER(canvas), evbox);
 	gtk_container_add(GTK_CONTAINER(evbox), darea);
 
-	draw_image(darea, s);
+	draw_image(darea, s, 0);
 
 	g_signal_connect(G_OBJECT(evbox), "scroll-event",
 	    G_CALLBACK(scroll_event), s);
 	g_signal_connect(G_OBJECT(darea), "expose-event",
 	    G_CALLBACK(expose_event), s);
+	g_signal_connect(G_OBJECT(darea), "motion-notify-event",
+	    G_CALLBACK(motion_notify_event), s);
+
 }
diff --git a/solidify/style.h b/solidify/style.h
index aff1c42..14bb978 100644
--- a/solidify/style.h
+++ b/solidify/style.h
@@ -19,8 +19,10 @@
 extern GdkGC *gc_osd;
 
 
-#define	OSD_PROXIMITY		20
-#define	LEVEL_CENTER_DIV	5
+#define	OSD_PROXIMITY		20	/* pixels */
+#define	LEVEL_CENTER_DIV	5	/* fraction of diagonal */
+#define	OVERLAP_BORDER		10	/* pixels around min. drawing area */
+#define	OVERLAP_CENTER_DIV	5	/* fraction of diagonal */
 
 
 void init_style(GdkDrawable *da);