diff --git a/ptrude/Makefile b/ptrude/Makefile
index c85c38a..5e20068 100644
--- a/ptrude/Makefile
+++ b/ptrude/Makefile
@@ -42,7 +42,7 @@ endif
 $(MAIN):		$(OBJS)
 
 try:		$(MAIN)
-		./$(MAIN) <try | tee out
+		./$(MAIN) -d try 1 0.1 | tee out
 
 clean:
 		rm -f $(OBJS) $(OBJS:.o=.d)
diff --git a/ptrude/path.c b/ptrude/path.c
index a9f14f8..bdd2e78 100644
--- a/ptrude/path.c
+++ b/ptrude/path.c
@@ -15,6 +15,7 @@
 #include <string.h>
 #include <math.h>
 
+#include "ptrude.h"
 #include "path.h"
 
 
@@ -169,13 +170,16 @@ static const struct vertex *corner(struct path *path, const struct vertex *a,
 	 */
 	dd = hypot(r, s)-r;
 
-	fprintf(stderr, "a = (%g, %g)-(%g, %g) = (%g, %g); |a| = %g\n",
-	    b->x, b->y, a->x, a->y, ax, ay, aa);
-	fprintf(stderr, "b = (%g, %g)-(%g, %g) = (%g, %g); |b| = %g\n",
-	    c->x, c->y, b->x, b->y, bx, by, bb);
-	fprintf(stderr, "sin 2t = %g, cos 2t = %g, tan t = %g\n",
-	    cp/aa/bb, dp/aa/bb, tt);
-	fprintf(stderr, "r = %g, d = %g, s = %g, dd = %g\n", r, d, s, dd);
+	if (debug) {
+		fprintf(stderr, "a = (%g, %g)-(%g, %g) = (%g, %g); |a| = %g\n",
+		    b->x, b->y, a->x, a->y, ax, ay, aa);
+		fprintf(stderr, "b = (%g, %g)-(%g, %g) = (%g, %g); |b| = %g\n",
+		    c->x, c->y, b->x, b->y, bx, by, bb);
+		fprintf(stderr, "sin 2t = %g, cos 2t = %g, tan t = %g\n",
+		    cp/aa/bb, dp/aa/bb, tt);
+		fprintf(stderr, "r = %g, d = %g, s = %g, dd = %g\n",
+		    r, d, s, dd);
+	}
 
 	/*
 	 * We only know how to make a rounded corner if two vectors are
@@ -228,8 +232,9 @@ static const struct vertex *corner(struct path *path, const struct vertex *a,
 
 	q = acos((r-d)/(r+d));
 
-	fprintf(stderr, "t2 = %g, p(max) = %g, q(max) = %g\n",
-	    deg(t2), deg(p), deg(q));
+	if (debug)
+		fprintf(stderr, "t2 = %g, p(max) = %g, q(max) = %g\n",
+		    deg(t2), deg(p), deg(q));
 
 	/*
 	 * Step 4: emit the starting point of the arc
@@ -279,8 +284,9 @@ static const struct vertex *corner(struct path *path, const struct vertex *a,
 		for (i = 0; i <= n; i++) {
 			x += f*ax*cos(ang-q)-dir*f*ay*sin(ang-q);
 			y += dir*f*ax*sin(ang-q)+f*ay*cos(ang-q);
-			fprintf(stderr, "  %d/%d: %g %g @ %g\n", i, n,
-			    x, y, deg(ang));
+			if (debug)
+				fprintf(stderr, "  %d/%d: %g %g @ %g\n", i, n,
+				    x, y, deg(ang));
 			add_vertex(path, x, y, 0, 0, NULL);
 			ang += 2*q;
 			f = (2*v)/aa;
diff --git a/ptrude/ptrude.c b/ptrude/ptrude.c
index dff3533..4520083 100644
--- a/ptrude/ptrude.c
+++ b/ptrude/ptrude.c
@@ -10,18 +10,107 @@
  * (at your option) any later version.
  */
 
+#include <stdlib.h>
 #include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <math.h>
 
 #include "path.h"
+#include "ptrude.h"
 
 
-int main(void)
+int debug = 0;
+
+
+static FILE *open_file(const char *name, const char *mode)
 {
-	const struct path *path;
+	FILE *file;
 
-	path = load_path(stdin);
-	path = round_path(path, 1, 0.1);
-	save_path(stdout, path);
+	if (!strcmp(name, "-"))
+		return strcmp(mode, "r") ? stdout : stdin;
+
+	file = fopen(name, mode);
+	if (!file) {
+		perror(name);
+		exit(1);
+	}
+	return file;
+}
+
+
+static void close_file(FILE *file)
+{
+	if (file == stdin || file == stdout)
+		return;
+	if (fclose(file) == EOF) {
+		perror("fclose");
+		exit(1);
+	}
+}
+
+
+static void usage(const char *name)
+{
+	fprintf(stderr,
+"usage: %s shape radius tolerance\n"
+"%6s %s path shape radius tolerance\n",
+	    name, "", name);
+	exit(1);
+}
+
+
+int main(int argc, char **argv)
+{
+	FILE *file;
+	const struct path *path = NULL, *shape;
+	double r, d;
+	char *end;
+	int c;
+
+	while ((c = getopt(argc, argv, "d")) != EOF)
+		switch (c) {
+		case 'd':
+			debug = 1;
+			break;
+		default:
+			usage(*argv);
+		}
+
+	switch (argc-optind) {
+	case 3:
+		break;
+	case 4:
+		file = open_file(argv[optind], "r");
+		path = load_path(file);
+		close_file(file);
+		break;
+	default:
+		usage(*argv);
+	}
+
+	file = open_file(argv[argc-3], "r");
+	shape = load_path(file);
+	close_file(file);
+
+	r = strtod(argv[argc-2], &end);
+	if (*end || r <= 0)
+		usage(*argv);
+	d = strtod(argv[argc-1], &end);
+	if (*end || d <= 0)
+		usage (*argv);
+
+	if (path) {
+		/*
+		 * We split the error budget evenly between path and shape.
+		 */
+		path = round_path(path, r, sqrt(d));
+		shape = round_path(shape, r, sqrt(d));
+		/* ... now all that's missing is the extrusion :-) */
+	} else {
+		shape = round_path(shape, r, d);
+		save_path(stdout, shape);
+	}
 
 	return 0;
 }
diff --git a/ptrude/ptrude.h b/ptrude/ptrude.h
new file mode 100644
index 0000000..3eb571f
--- /dev/null
+++ b/ptrude/ptrude.h
@@ -0,0 +1,18 @@
+/*
+ * ptrude.h - Extrusion of a 2D path along a perpendicular 2D path
+ *
+ * Written 2011 by Werner Almesberger
+ * Copyright 2011 by Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+#ifndef PTRUDE_H
+#define	PTRUDE_H
+
+extern int debug;
+
+#endif /* !PTRUDE_H */