diff --git a/cameo/stl.c b/cameo/stl.c
index ef56445..f9b1fb7 100644
--- a/cameo/stl.c
+++ b/cameo/stl.c
@@ -11,7 +11,9 @@
  */
 
 
+#include <stdlib.h>
 #include <stdio.h>
+#include <math.h>
 
 #include "poly2d.h"
 
@@ -19,20 +21,79 @@
 #include "stl.h"
 
 
-void stl(const char *name, const struct path *paths)
+static void facet(FILE *file, const struct f2d *f, int a, int b, int c,
+    double za, double zb, double zc,  double nx, double ny, double nz)
+{
+	double d;
+
+	d = sqrt(nx*nx+ny*ny+nz*nz);
+	if (!d)
+		d = 1;
+
+	fprintf(file, "facet normal %e %e %e\n", nx/d, ny/d, nz/d);
+	fprintf(file, "\touter loop\n");
+	fprintf(file, "\t\tvertex %e %e %e\n", f->x[a], f->y[a], za);
+	fprintf(file, "\t\tvertex %e %e %e\n", f->x[b], f->y[b], zb);
+	fprintf(file, "\t\tvertex %e %e %e\n", f->x[c], f->y[c], zc);
+	fprintf(file, "\tendloop\n");
+	fprintf(file, "endfacet\n");
+}
+
+
+static void surface(FILE *file, const struct f2d *f)
+{
+	facet(file, f, 0, 1, 2, 1, 1, 1, 0, 0, 1);
+	facet(file, f, 2, 1, 0, 0, 0, 0, 0, 0, -1);
+}
+
+
+static void side(FILE *file, const struct f2d *f, int a, int b)
+{
+	double nx, ny;
+
+	nx = f->y[b]-f->y[a];
+	ny = f->x[a]-f->x[b];
+	facet(file, f, a, b, b, 0, 0, 1, nx, ny, 0);
+	facet(file, f, b, a, a, 1, 1, 0, nx, ny, 0);
+}
+
+
+static void stl_write(FILE *file, const struct path *paths)
 {
 	struct p2d *polys;
 	struct f2d *faces;
 	const struct f2d *f;
+	int i;
 
+	fprintf(file, "solid cameo\n");
 	polys = paths_to_polys(paths);
 	faces = f2d_tri(polys);
-	for (f = faces; f; f = f->next)
-		printf("%f/%f %f/%f %f/%f  (%d %d %d)\n",
-		    f->x[0], f->y[0],
-		    f->x[1], f->y[1],
-		    f->x[2], f->y[2],
-		    f->side[0], f->side[1], f->side[2]);
+	for (f = faces; f; f = f->next) {
+		surface(file, f);
+		for (i = 0; i != 3; i++)
+			if (f->side[i])
+				side(file, f, i, (i+1) % 3);
+	}
 	p2d_free_all(polys);
 	f2d_free_all(faces);
+	fprintf(file, "endsolid cameo\n");
+}
+
+
+void stl(const char *name, const struct path *paths)
+{
+	FILE *file = stdout;
+
+	if (name) {
+		file = fopen(name, "w");
+		if (!file) {
+			perror(name);
+			exit(1);
+		}
+	}
+	stl_write(file, paths);
+	if (name && fclose(file)) {
+		perror(name);
+		exit(1);
+	}
 }