diff --git a/Makefile b/Makefile
index 42d3ae5..87a3338 100644
--- a/Makefile
+++ b/Makefile
@@ -10,12 +10,13 @@ CFLAGS = \
 LDLIBS = \
 	-lm \
 
-all: unfold wireframe corners faces
+all: unfold wireframe corners faces hiddenwire
 
 unfold: unfold.o
 wireframe: wireframe.o
 corners: corners.o stl_3d.o
 faces: faces.o stl_3d.o
+hiddenwire: hiddenwire.o camera.o
 
 clean:
 	$(RM) *.o
diff --git a/camera.c b/camera.c
new file mode 100644
index 0000000..1a6ed11
--- /dev/null
+++ b/camera.c
@@ -0,0 +1,102 @@
+/** \file
+ * 3D camera equation.
+ *
+ * Given a camera matrix and a XYZ point, returns the 2D coordinate
+ * of the point.
+ */
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "camera.h"
+
+struct _camera_t
+{
+	float	zoom;
+	float	eye_z;
+	float	r[3][3];
+};
+
+
+camera_t *
+camera_new(
+	float eye_z,
+	float phi,
+	float theta,
+	float psi
+)
+{
+	camera_t * c = calloc(1, sizeof(*c));
+	if (!c)
+		return NULL;
+
+	c->zoom = 1024;
+	camera_setup(c, eye_z, phi, theta, psi);
+	return c;
+}
+
+
+void
+camera_setup(
+	camera_t * const c,
+	float eye_z,
+	float phi,
+	float theta,
+	float psi
+)
+{
+	const float sx = sin(phi);
+	const float cx = cos(phi);
+	const float sy = sin(theta);
+	const float cy = cos(theta);
+	const float sz = sin(psi);
+	const float cz = cos(psi);
+
+	c->r[0][0] =   cy * cz;
+	c->r[0][1] = (-cy * sz) + (sx * sy * cz);
+	c->r[0][2] = ( sx * sz) + (cx * sy * cz);
+
+	c->r[1][0] =   cx * sz;
+	c->r[1][1] = ( cx * cz) + (sx * sy * sz);
+	c->r[1][2] = (-sx * cz) + (cx * sy * sz);
+
+	c->r[2][0] = -sy;
+	c->r[2][1] =  sx * cy;
+	c->r[2][2] =  cx * cy;
+
+	c->eye_z = eye_z;
+ }
+
+
+/** Transform a XYZ point into a screen point.
+ *
+ * Returns 0 if this is behind us.  Perhaps it should do a z buffer?
+ */
+int
+camera_project(
+	const camera_t * const c,
+	const v3_t * const v,
+	v3_t * const v_out
+)
+{
+	v3_t p = { .p = { 0, 0, c->eye_z } };
+
+	for (int i = 0 ; i < 3 ; i++)
+		for (int j = 0 ; j < 3 ; j++)
+			p.p[i] += c->r[i][j] * v->p[j];
+
+	// what if p->p[2] == 0?
+
+	// Transform to screen coordinate frame,
+	// is this rotating?
+	float px = p.p[1] / p.p[2];
+	float py = p.p[0] / p.p[2];
+	float pz = p.p[2];
+
+	// return it to the caller
+	v_out->p[0] = px * c->zoom;
+	v_out->p[1] = py * c->zoom;
+	v_out->p[2] = pz * c->zoom;
+
+	// pz < 0 == The point is behind us; do not display?
+	return pz <= 0 ? 0 : 1;
+}
diff --git a/camera.h b/camera.h
new file mode 100644
index 0000000..042d079
--- /dev/null
+++ b/camera.h
@@ -0,0 +1,35 @@
+#pragma once
+
+#include "v3.h"
+
+typedef struct _camera_t camera_t;
+
+extern camera_t *
+camera_new(
+	float eye_z,
+	float phi,
+	float theta,
+	float psi
+);
+
+extern void
+camera_setup(
+	camera_t * const c,
+	float eye_z,
+	float phi,
+	float theta,
+	float psi
+);
+
+/** Transform a XYZ point into a screen point.
+ *
+ * Returns 0 if this is behind us.  Perhaps it should do a z buffer?
+ */
+extern int
+camera_project(
+	const camera_t * const c,
+	const v3_t * const v,
+	v3_t * const v_out
+);
+
+
diff --git a/hiddenwire.c b/hiddenwire.c
new file mode 100644
index 0000000..d661288
--- /dev/null
+++ b/hiddenwire.c
@@ -0,0 +1,845 @@
+/** \file
+ * Render a hidden wireframe version of an STL file.
+ *
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdarg.h>
+#include <unistd.h>
+#include <math.h>
+#include <err.h>
+#include <assert.h>
+#include "v3.h"
+#include "camera.h"
+
+#ifndef M_PI
+#define 	M_PI   3.1415926535897932384
+#endif
+
+static int debug = 0;
+static int draw_labels = 0;
+
+typedef struct
+{
+	char header[80];
+	uint32_t num_triangles;
+} __attribute__((__packed__))
+stl_header_t;
+
+
+typedef struct
+{
+	v3_t normal;
+	v3_t p[3];
+	uint16_t attr;
+} __attribute__((__packed__))
+stl_face_t;
+
+#if 0
+typedef struct face face_t;
+typedef struct poly poly_t;
+
+struct face
+{
+	float sides[3];
+	face_t * next[3];
+	int next_edge[3];
+	int coplanar[3];
+	int used;
+};
+
+// once this triangle has been used, it will be placed
+// in a polygon group and fixed in a position relative to that group
+struct poly
+{
+	int start_edge;
+	int printed;
+
+	// local coordinates of the triangle vertices
+	float a;
+	float x2;
+	float y2;
+	float rot;
+
+	// absolute coordintes of the triangle vertices
+	float p[3][2];
+
+	// todo: make this const and add backtracking
+	face_t * face;
+	poly_t * next[3];
+
+	poly_t * work_next;
+};
+
+
+/* Compare two edges in two triangles.
+ *
+ * note that if the windings are all the same, the edges will
+ * compare in the opposite order (for example, the edge from 0 to 1
+ * compares to the edge from 2 to 1 in the other triangle).
+ */
+static int
+edge_eq2(
+	const stl_face_t * const t0,
+	const stl_face_t * const t1,
+	int e0,
+	int e1
+)
+{
+	const v3_t * const v00 = &t0->p[e0];
+	const v3_t * const v01 = &t0->p[(e0+1) % 3];
+
+	const v3_t * const v10 = &t1->p[e1];
+	const v3_t * const v11 = &t1->p[(e1+1) % 3];
+
+	if (v3_eq(v00, v11) && v3_eq(v01, v10))
+		return 1;
+
+	return 0;
+}
+#endif
+
+
+void
+svg_line(
+	const char * color,
+	const float * p1,
+	const float * p2,
+	int dash
+)
+{
+	if (!dash)
+	{
+		printf("<line x1=\"%f\" y1=\"%f\" x2=\"%f\" y2=\"%f\" stroke=\"%s\" stroke-width=\"0.1px\"/>\n",
+			p1[0],
+			p1[1],
+			p2[0],
+			p2[1],
+			color
+		);
+		return;
+	}
+
+	// dashed line, split in the middle
+	const float dx = p2[0] - p1[0];
+	const float dy = p2[1] - p1[1];
+
+	const float h1[] = {
+		p1[0] + dx*0.45,
+		p1[1] + dy*0.45,
+	};
+	const float h2[] = {
+		p1[0] + dx*0.55,
+		p1[1] + dy*0.55,
+	};
+
+
+	svg_line(color, p1, h1, 0);
+	svg_line(color, h2, p2, 0);
+}
+
+
+#if 0
+void
+rotate(
+	float * p,
+	const float * origin,
+	float a,
+	float x,
+	float y
+)
+{
+	p[0] = cos(a) * x - sin(a) * y + origin[0];
+	p[1] = sin(a) * x + cos(a) * y + origin[1];
+}
+
+
+/* Rotate and translate a triangle */
+void
+poly_position(
+	poly_t * const g,
+	const poly_t * const g_src,
+	float rot,
+	float trans_x,
+	float trans_y
+)
+{
+	const face_t * const f = g->face;
+	const int start_edge = g->start_edge;
+
+	float a = f->sides[(start_edge + 0) % 3];
+	float c = f->sides[(start_edge + 1) % 3];
+	float b = f->sides[(start_edge + 2) % 3];
+	float x2 = (a*a + b*b - c*c) / (2*a);
+	float y2 = sqrt(b*b - x2*x2);
+
+	// translate by trans_x/trans_y in the original ref frame
+	// to get the origin point
+	float origin[2];
+	rotate(origin, g_src->p[0], g_src->rot, trans_x, trans_y);
+
+	g->rot = g_src->rot + rot;
+	g->a = a;
+	g->x2 = x2;
+	g->y2 = y2;
+
+//fprintf(stderr, "%p %d %f %f %f %f => %f %f %f\n", f, start_edge, g->rot*180/M_PI, a, b, c, x2, y2, rot);
+	rotate(g->p[0], origin, g->rot, 0, 0);
+	rotate(g->p[1], origin, g->rot, a, 0);
+	rotate(g->p[2], origin, g->rot, x2, y2);
+}
+
+
+static void
+enqueue(
+	poly_t * g,
+	poly_t * const new_g,
+	int at_head
+)
+{
+	if (at_head)
+	{
+		new_g->work_next = g->work_next;
+		g->work_next = new_g;
+		return;
+	}
+
+	// go to the end of the line
+	while (g->work_next)
+		g = g->work_next;
+	g->work_next = new_g;
+}
+
+
+static poly_t * poly_root;
+static float poly_min[2], poly_max[2];
+
+static inline int
+v2_eq(
+	const float p0[],
+	const float p1[]
+)
+{
+	const float dx = p0[0] - p1[0];
+	const float dy = p0[1] - p1[1];
+
+	// are the points within epsilon of each other?
+	if (-EPS < dx && dx < EPS
+	&&  -EPS < dy && dy < EPS)
+		return 1;
+
+	// nope, not equal
+	return 0;
+}
+
+
+
+// Returns 1 if the lines intersect, otherwise 0. In addition, if the lines 
+// intersect the intersection point may be stored in the floats i_x and i_y.
+int
+get_line_intersection(
+	float p0_x,
+	float p0_y,
+	float p1_x,
+	float p1_y, 
+	float p2_x,
+	float p2_y,
+	float p3_x,
+	float p3_y,
+	float *i_x,
+	float *i_y
+)
+{
+	float s1_x = p1_x - p0_x;
+	float s1_y = p1_y - p0_y;
+	float s2_x = p3_x - p2_x;
+	float s2_y = p3_y - p2_y;
+
+	float s = (-s1_y * (p0_x - p2_x) + s1_x * (p0_y - p2_y))
+		/ (-s2_x * s1_y + s1_x * s2_y);
+
+	float t = ( s2_x * (p0_y - p2_y) - s2_y * (p0_x - p2_x))
+		/ (-s2_x * s1_y + s1_x * s2_y);
+
+	if (s > EPS && s < 1-EPS && t > EPS && t < 1-EPS)
+	{
+		if(debug) fprintf(stderr, "collision: %f,%f->%f,%f %f,%f->%f,%f == %f,%f\n",
+			p0_x, p0_y,
+			p1_x, p1_y,
+			p2_x, p2_y,
+			p3_x, p3_y,
+			s,
+			t
+		);
+
+		// Collision detected
+		if (i_x != NULL)
+			*i_x = p0_x + (t * s1_x);
+		if (i_y != NULL)
+			*i_y = p0_y + (t * s1_y);
+		return 1;
+	}
+
+	return 0; // No collision
+}
+
+
+int
+intersect(
+	const float p00[],
+	const float p01[],
+	const float p10[],
+	const float p11[]
+)
+{
+	// special case; if this is the same line, it does not intersect
+	if (v2_eq(p00, p10) && v2_eq(p01, p11))
+		return 0;
+	if (v2_eq(p01, p10) && v2_eq(p00, p11))
+		return 0;
+
+	return get_line_intersection(
+		p00[0],
+		p00[1],
+		p01[0],
+		p01[1],
+		p10[0],
+		p10[1],
+		p11[0],
+		p11[1],
+		NULL,
+		NULL
+	);
+}
+
+
+/** Check to see if two triangles overlap */
+int
+overlap_poly(
+	const poly_t * const g1,
+	const poly_t * const g2
+)
+{
+	if (intersect(g1->p[0], g1->p[1], g2->p[0], g2->p[1]))
+		return 1;
+	if (intersect(g1->p[0], g1->p[1], g2->p[1], g2->p[2]))
+		return 1;
+	if (intersect(g1->p[0], g1->p[1], g2->p[2], g2->p[0]))
+		return 1;
+
+	if (intersect(g1->p[1], g1->p[2], g2->p[0], g2->p[1]))
+		return 1;
+	if (intersect(g1->p[1], g1->p[2], g2->p[1], g2->p[2]))
+		return 1;
+	if (intersect(g1->p[1], g1->p[2], g2->p[2], g2->p[0]))
+		return 1;
+
+	if (intersect(g1->p[2], g1->p[0], g2->p[0], g2->p[1]))
+		return 1;
+	if (intersect(g1->p[2], g1->p[0], g2->p[1], g2->p[2]))
+		return 1;
+	if (intersect(g1->p[2], g1->p[0], g2->p[2], g2->p[0]))
+		return 1;
+
+	return 0;
+}
+
+
+/** Check to see if any triangles overlap */
+int
+overlap_check(
+	const poly_t * g,
+	const poly_t * const new_g
+)
+{
+	// special case -- if the root is the same as the one that we
+	// are checking, then it does not overlap
+	if (g == new_g)
+		return 0;
+
+	while (g)
+	{
+		if (overlap_poly(g, new_g))
+			return 1;
+		g = g->work_next;
+	}
+
+	return 0;
+}
+
+
+/** recursively try to fix up the triangles.
+ *
+ * returns the maximum number of triangles added
+ */
+int
+poly_build(
+	poly_t * const g
+)
+{
+	face_t * const f = g->face;
+	const int start_edge = g->start_edge;
+	f->used = 1;
+
+	// update the group's bounding box
+	for (int i = 0 ; i < 3 ; i++)
+	{
+		const float px = g->p[i][0];
+		const float py = g->p[i][1];
+
+		if (px < poly_min[0]) poly_min[0] = px;
+		if (px > poly_max[0]) poly_max[0] = px;
+
+		if (py < poly_min[1]) poly_min[1] = py;
+		if (py > poly_max[1]) poly_max[1] = py;
+	}
+		
+
+	if (debug) fprintf(stderr, "%p: adding to poly\n", f);
+
+   for(int pass = 0 ; pass < 2 ; pass++)
+   {
+	// for each edge, find the triangle that matches
+	for (int i = 0 ; i < 3 ; i++)
+	{
+		const int edge = (i + start_edge) % 3;
+		face_t * const f2 = f->next[edge];
+		assert(f2 != NULL);
+		if (f2->used)
+			continue;
+		if (pass == 0 && f->coplanar[edge] == 0)
+			continue;
+
+		// create a group that translates and rotates
+		// such that it lines up with this edge
+		float trans_x, trans_y, rotate;
+		if (i == 0)
+		{
+			trans_x = g->a;
+			trans_y = 0;
+			rotate = M_PI;
+		} else
+		if (i == 1)
+		{
+			trans_x = g->x2;
+			trans_y = g->y2;
+			rotate = -atan2(g->y2, g->a - g->x2);
+		} else
+		if (i == 2)
+		{
+			trans_x = 0;
+			trans_y = 0;
+			rotate = atan2(g->y2, g->x2);
+		} else {
+			errx(EXIT_FAILURE, "edge %d invalid?\n", i);
+		}
+
+		// position this one translated and rotated
+		poly_t * const g2 = calloc(1, sizeof(*g2));
+		g2->face = f2;
+		g2->start_edge = f->next_edge[edge];
+
+		poly_position(
+			g2,
+			g,
+			rotate, 
+			trans_x,
+			trans_y
+		);
+
+		if (overlap_check(poly_root, g2))
+		{
+			free(g2);
+			continue;
+		}
+
+		// no overlap, add it to the current group
+		g->next[i] = g2;
+		g2->next[0] = g;
+		f2->used = 1;
+
+		// if g2 is a coplanar triangle, process it now rather than
+		// defering the work.
+		if (f->coplanar[edge] == 0)
+			enqueue(g, g2, 1);
+		else
+			enqueue(g, g2, 0);
+	}
+    }
+
+	return 0;
+}
+
+
+void
+svg_text(
+	float x,
+	float y,
+	float angle,
+	const char * fmt,
+	...
+)
+{
+
+	printf("<g transform=\"translate(%f %f) rotate(%f)\">",
+		x,
+		y,
+		angle
+	);
+
+	printf("<text x=\"-2\" y=\"1.5\" style=\"font-size:1.5px;\">");
+
+	va_list ap;
+	va_start(ap, fmt);
+	vprintf(fmt, ap);
+	va_end(ap);
+
+	printf("</text></g>\n");
+}
+
+void
+poly_print(
+	poly_t * const g
+)
+{
+	const face_t * const f = g->face;
+	const int start_edge = g->start_edge;
+
+	g->printed = 1;
+
+	// draw this triangle;
+	// if the edge is an outside, which means that the group
+	// has no next element, draw a cut line.  If there is an
+	// adjacent neighbor and it is not coplanar, draw a score line
+printf("<g><!-- %p %d %f %f->%p %f->%p %f->%p -->\n",
+	f,
+	g->start_edge, g->rot * 180/M_PI,
+	f->sides[0],
+	f->next[0],
+	f->sides[1],
+	f->next[1],
+	f->sides[2],
+	f->next[2]
+);
+
+	int cut_lines = 0;
+	const uintptr_t a1 = (0x7FFFF & (uintptr_t) f) >> 3;
+
+	for (int i = 0 ; i < 3 ; i++)
+	{
+		const int edge = (start_edge + i) % 3;
+		poly_t * const next = g->next[i];
+
+		if (!next)
+		{
+			// draw a cut line
+			const float * const p1 = g->p[i];
+			const float * const p2 = g->p[(i+1) % 3];
+			const float cx = (p2[0] + p1[0]) / 2;
+			const float cy = (p2[1] + p1[1]) / 2;
+			const float dx = (p2[0] - p1[0]);
+			const float dy = (p2[1] - p1[1]);
+			const float angle = atan2(dy, dx) * 180 / M_PI;
+
+			svg_line("#FF0000", p1, p2, 0);
+			cut_lines++;
+
+			// use the lower address as the label
+			if (draw_labels)
+			{
+				uintptr_t a2 = (0x7FFFF & (uintptr_t) f->next[edge]) >> 3;
+				if (a2 > a1)
+					a2 = a1;
+				svg_text(cx, cy, angle, "%04x", a2);
+			}
+
+			continue;
+		}
+
+		if (next->printed)
+			continue;
+
+		if (f->coplanar[edge] < 0)
+		{
+			// draw a mountain score line since they are not coplanar
+			svg_line("#00FF00", g->p[i], g->p[(i+1) % 3], 1);
+		} else
+		if (f->coplanar[edge] > 0)
+		{
+			// draw a valley score line since they are not coplanar
+			svg_line("#00FF00", g->p[i], g->p[(i+1) % 3], 0);
+		} else {
+			// draw a shadow line since they are coplanar
+			//svg_line("#F0F0F0", g->p[i], g->p[(i+1) % 3]);
+		}
+	}
+
+/*
+	// only draw labels if requested and if there are any cut-edges
+	// on this polygon.
+	const float tx = (g->p[0][0] + g->p[1][0] + g->p[2][0]) / 3.0;
+	const float ty = (g->p[0][1] + g->p[1][1] + g->p[2][1]) / 3.0;
+	if (draw_labels && cut_lines > 0)
+	svg_text(tx, ty, 0, "%04x",
+		(0x7FFFF & (uintptr_t) f) >> 3);
+*/
+
+printf("</g>\n");
+
+	for (int i = 0 ; i < 3 ; i++)
+	{
+		poly_t * const next = g->next[i];
+		if (!next || next->printed)
+			continue;
+
+		poly_print(next);
+	}
+}
+
+
+/* Returns the 0 for coplanar, negative for mountain, positive for valley.
+ * (approximates the angle between two triangles that share one edge).
+ */
+int
+coplanar_check(
+	const stl_face_t * const f1,
+	const stl_face_t * const f2
+)
+{
+	// find the four distinct points
+	v3_t x1 = f1->p[0];
+	v3_t x2 = f1->p[1];
+	v3_t x3 = f1->p[2];
+	v3_t x4;
+
+	for (int i = 0 ; i < 3 ; i++)
+	{
+		x4 = f2->p[i];
+		if (v3_eq(&x1, &x4))
+			continue;
+		if (v3_eq(&x2, &x4))
+			continue;
+		if (v3_eq(&x3, &x4))
+			continue;
+		break;
+	}
+
+	// (x3-x1) . ((x2-x1) X (x4-x3)) == 0
+	v3_t dx31 = v3_sub(x3, x1);
+	v3_t dx21 = v3_sub(x2, x1);
+	v3_t dx43 = v3_sub(x4, x3);
+	v3_t cross = v3_cross(dx21, dx43);
+	float dot = v3_dot(dx31, cross);
+	
+	int check = -EPS < dot && dot < +EPS;
+	if (debug) fprintf( stderr, "%p %p %s: %f\n", f1, f2, check ? "yes" : "no", dot);
+	return (int) dot;
+}
+
+
+/** Translate a list of STL triangles into a connected graph of faces.
+ *
+ * If there are any triangles that do not have three connected edges,
+ * the first error will be reported and NULL will be returned.
+ */
+face_t *
+stl2faces(
+	const stl_face_t * const stl_faces,
+	const int num_triangles
+)
+{
+	face_t * const faces = calloc(num_triangles, sizeof(*faces));
+
+	// convert the stl triangles into faces
+	for (int i = 0 ; i < num_triangles ; i++)
+	{
+		const stl_face_t * const stl = &stl_faces[i];
+		face_t * const f = &faces[i];
+
+		f->sides[0] = v3_len(&stl->p[0], &stl->p[1]);
+		f->sides[1] = v3_len(&stl->p[1], &stl->p[2]);
+		f->sides[2] = v3_len(&stl->p[2], &stl->p[0]);
+		if (debug) fprintf(stderr, "%p %f %f %f\n",
+			f, f->sides[0], f->sides[1], f->sides[2]);
+	}
+
+	// look to see if there is a matching point
+	// in the faces that we've already built
+	for (int i = 0 ; i < num_triangles ; i++)
+	{
+		const stl_face_t * const stl = &stl_faces[i];
+		face_t * const f = &faces[i];
+
+		for (int j = 0 ; j < num_triangles ; j++)
+		{
+			if (i == j)
+				continue;
+
+			const stl_face_t * const stl2 = &stl_faces[j];
+			face_t * const f2 = &faces[j];
+
+			for (int edge = 0 ; edge < 3 ; edge++)
+			{
+				if (f->next[edge])
+					continue;
+
+				for (int edge2 = 0 ; edge2 < 3 ; edge2++)
+				{
+					if (f2->next[edge2])
+						continue;
+
+					if (!edge_eq2(stl, stl2, edge, edge2))
+						continue;
+
+					f->next[edge] = f2;
+					f->next_edge[edge] = edge2;
+					f2->next[edge2] = f;
+					f2->next_edge[edge2] = edge;
+
+					f->coplanar[edge] =
+					f2->coplanar[edge2] = coplanar_check(stl, stl2);
+				}
+			}
+		}
+
+		// all three edges should be matched
+		if (f->next[0] && f->next[1] && f->next[2])
+			continue;
+		fprintf(stderr, "%d missing edges?\n", i);
+		free(faces);
+		return NULL;
+	}
+
+	return faces;
+}
+#endif
+
+
+int main(void)
+{
+	const size_t max_len = 1 << 20;
+	uint8_t * const buf = calloc(max_len, 1);
+
+	ssize_t rc = read(0, buf, max_len);
+	if (rc == -1)
+		return EXIT_FAILURE;
+
+	const stl_header_t * const hdr = (const void*) buf;
+	const stl_face_t * const stl_faces = (const void*)(hdr+1);
+	const int num_triangles = hdr->num_triangles;
+
+	fprintf(stderr, "header: '%s'\n", hdr->header);
+	fprintf(stderr, "num: %d\n", num_triangles);
+
+
+	// looking at (0,0,0)
+	const camera_t * const cam = camera_new(400, 0, M_PI/2, M_PI);
+
+	// translate each face into lines
+	printf("<svg xmlns=\"http://www.w3.org/2000/svg\">\n");
+	printf("<g>\n");
+
+	// convert the stl triangles into faces
+	for (int i = 0 ; i < num_triangles ; i++)
+	{
+		const stl_face_t * const stl = &stl_faces[i];
+
+		v3_t s[3];
+
+		for(int j = 0 ; j < 3 ; j++)
+			camera_project(cam, &stl->p[j], &s[j]);
+
+		// draw each of the three lines
+		for(int j = 0 ; j < 3 ; j++)
+		{
+			if (s[j].p[2] <= 0)
+				continue;
+			if (s[(j+1) % 3].p[2] <= 0)
+				continue;
+			svg_line("#FF0000", s[j].p, s[(j+1) % 3].p, 0);
+		}
+
+	}
+
+#if 0
+	face_t * const faces = stl2faces(stl_faces, num_triangles);
+
+	// we now have a graph that shows the connection between
+	// all of the faces and their sizes. start trying to build
+	// non-overlapping groups of them
+	
+	poly_t origin = { };
+
+	float last_x = 0;
+	float last_y = 0;
+
+	srand48(getpid());
+
+	int offset;
+
+	const char * const poly_offset = getenv("POLY");
+	if (poly_offset)
+		offset = atoi(poly_offset);
+	else
+		offset = lrand48();
+	fprintf(stderr, "Starting at poly %d\n", offset % num_triangles);
+	int group_count = 0;
+
+	for (int i = 0 ; i < num_triangles ; i++)
+	{
+		face_t * const f = &faces[(i+offset) % num_triangles];
+		if (f->used)
+			continue;
+		poly_t g = {
+			.face	= f,
+			.start_edge	= 0,
+		};
+		poly_position(&g, &origin, 0, 0, 0);
+
+		// set the root of the new group
+		poly_root = &g;
+		poly_min[0] = poly_min[1] = 0;
+		poly_max[0] = poly_max[1] = 0;
+
+		poly_t * iter = &g;
+		int poly_count = 0;
+		group_count++;
+
+		if (debug) fprintf(stderr, "****** %d: New group %p\n",
+			group_count, poly_root);
+
+		while (iter)
+		{
+			poly_build(iter);
+			iter = iter->work_next;
+			poly_count++;
+		}
+
+		fprintf(stderr, "group %d: %d triangles\n",
+			group_count, poly_count);
+
+		// todo: walk the generated polygon and attempt to add tabs
+		// to edges where they fit
+
+
+		// offset the poly so that it doesn't overlap the ones
+		// we've already generated. only shift in Y.
+		float off_x = last_x - poly_min[0];
+		float off_y = last_y - poly_min[1];
+		last_y = off_y + poly_max[1];
+
+		// \todo: generate lots of poly sets before we print
+		// to find a minimal set. perhaps vary the search rules?
+
+		printf("<g transform=\"translate(%f %f)\">\n", off_x, off_y);
+		poly_print(&g);
+		printf("</g>\n");
+	}
+#endif
+
+	printf("</g>\n");
+	printf("</svg>\n");
+
+	return 0;
+}