Index: cdt.c
===================================================================
--- cdt.c	(revision 33746)
+++ cdt.c	(revision 33747)
@@ -465,6 +465,7 @@
 	retriangulation_region_t region = {NULL, NULL};
 	pointlist_node_t *points_to_attach, *prev_point_node;
 	point_t *split_edge_endp[2] = {NULL, NULL};
+	void *split_edge_user_data;
 	int i, j;
 
 	/* find enclosing triangle */
@@ -486,6 +487,9 @@
 			if (crossing_edge->is_constrained) {
 				for (j = 0; j < 2; j++)
 					split_edge_endp[j] = enclosing_triangle->e[i]->endp[j];
+				split_edge_user_data = crossing_edge->data;
+				if (cdt->ev_split_constrained_edge_pre != NULL)
+					cdt->ev_split_constrained_edge_pre(cdt, crossing_edge, new_p);
 				crossing_edge->is_constrained = 0;
 			}
 			break;
@@ -521,8 +525,11 @@
 
 	/* recreate, now splitted, constrained edge */
 	if (split_edge_endp[0] != NULL) {
-		cdt_insert_constrained_edge(cdt, split_edge_endp[0], new_p);
-		cdt_insert_constrained_edge(cdt, new_p, split_edge_endp[1]);
+		edge_t *e1 = cdt_insert_constrained_edge(cdt, split_edge_endp[0], new_p);
+		edge_t *e2 = cdt_insert_constrained_edge(cdt, new_p, split_edge_endp[1]);
+		e1->data = e2->data = split_edge_user_data;
+		if (cdt->ev_split_constrained_edge_post != NULL)
+			cdt->ev_split_constrained_edge_post(cdt, e1, e2, new_p);
 	}
 	return 0;
 }
Index: cdt.h
===================================================================
--- cdt.h	(revision 33746)
+++ cdt.h	(revision 33747)
@@ -33,15 +33,20 @@
 #include "edge.h"
 #include "triangle.h"
 
+typedef struct cdt_s cdt_t;
 
-typedef struct {
+struct cdt_s {
 	vtpoint_t points;
 	vtedge_t edges;
 	vttriangle_t triangles;
 
+	/* optional event callbacks (may be NULL to ignore) */
+	void (*ev_split_constrained_edge_pre)(cdt_t *cdt, edge_t *cedge, point_t *pt); /* called before removing a constrained edge that gets split at pt */
+	void (*ev_split_constrained_edge_post)(cdt_t *cdt, edge_t *ne1, edge_t *ne2, point_t *pt); /* called after creating the two new constrained edges around pt */
+
 	pos_t bbox_tl;
 	pos_t bbox_br;
-} cdt_t;
+};
 
 
 void cdt_init(cdt_t *cdt, coord_t bbox_x1, coord_t bbox_y1, coord_t bbox_x2, coord_t bbox_y2);
Index: cdt_test.c
===================================================================
--- cdt_test.c	(revision 33746)
+++ cdt_test.c	(revision 33747)
@@ -50,6 +50,20 @@
 	cdt_free(&cdt);
 }
 
+static int print_events = 0;
+
+static void ev_split_constrained_edge_pre(cdt_t *cdt, edge_t *cedge, point_t *pt)
+{
+	if (print_events)
+		printf("split_constrained_edge_pre at %d;%d\n", pt->pos.x, pt->pos.y);
+}
+
+static void ev_split_constrained_edge_post(cdt_t *cdt, edge_t *ne1, edge_t *ne2, point_t *pt)
+{
+	if (print_events)
+		printf("split_constrained_edge_post at %d;%d\n", pt->pos.x, pt->pos.y);
+}
+
 static void cmd_init(char *args)
 {
 	long x1, y1, x2, y2;
@@ -58,6 +72,8 @@
 		return;
 	}
 	cdt_init(&cdt, x1, y1, x2, y2);
+	cdt.ev_split_constrained_edge_pre = ev_split_constrained_edge_pre;
+	cdt.ev_split_constrained_edge_post = ev_split_constrained_edge_post;
 }
 
 static void cmd_free(char *args)
@@ -195,6 +211,17 @@
 	fclose(f);
 }
 
+static void cmd_print_events(char *args)
+{
+	switch(*args) {
+		case '1': case 'y': case 'Y': case 't': case 'T': print_events = 1; break;
+		case '0': case 'n': case 'N': case 'f': case 'F': print_events = 0; break;
+		default:
+			fprintf(stderr, "print_events: invalid boolean value '%s'\n", args);
+			return;
+	}
+}
+
 int main(void)
 {
 	char line[1024], *cmd, *args;
@@ -224,6 +251,7 @@
 		else if (strcmp(cmd, "ins_cedge") == 0) cmd_ins_cedge(args);
 		else if (strcmp(cmd, "del_cedge") == 0) cmd_del_cedge(args);
 		else if (strcmp(cmd, "dump_anim") == 0) cmd_dump_anim(args);
+		else if (strcmp(cmd, "print_events") == 0) cmd_print_events(args);
 		else fprintf(stderr, "syntax error: unknown command '%s'\n", cmd);
 	}
 	return 0;
Index: regression/split_cedge.cdt
===================================================================
--- regression/split_cedge.cdt	(revision 33746)
+++ regression/split_cedge.cdt	(revision 33747)
@@ -9,6 +9,8 @@
 # p4--------p3
 #
 
+# there should be one split printed, pre and post
+print_events yes
 
 # create the initial square
 init 0 0 1000 1000