commit 2bb95317408c25a34f7fc4a489008d112fe45669
Author: Trammell Hudson <hudson@osresearch.net>
Date:   Thu Dec 11 20:29:09 2014 -0500

    parse binary stl, merge vertices

diff --git a/Bunny-LowPoly.stl b/Bunny-LowPoly.stl
new file mode 100644
index 0000000..94a9566
Binary files /dev/null and b/Bunny-LowPoly.stl differ
diff --git a/unfold.c b/unfold.c
new file mode 100644
index 0000000..064891e
--- /dev/null
+++ b/unfold.c
@@ -0,0 +1,126 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <unistd.h>
+
+
+#define EPS 0.0001
+
+typedef struct
+{
+	char header[80];
+	uint32_t num_triangles;
+} __attribute__((__packed__))
+stl_header_t;
+
+typedef struct
+{
+	float p[3];
+} v3_t;
+
+typedef struct
+{
+	v3_t normal;
+	v3_t p0;
+	v3_t p1;
+	v3_t p2;
+} __attribute__((__packed__))
+stl_face_t;
+
+
+#define MAX_POINTS 24
+
+typedef struct
+{
+	int n;
+	int p[MAX_POINTS];
+} poly_t;
+
+
+static int
+v3_eq(
+	const v3_t * v1,
+	const v3_t * v2
+)
+{
+	float dx = v1->p[0] - v2->p[0];
+	float dy = v1->p[1] - v2->p[1];
+	float dz = v1->p[2] - v2->p[2];
+
+	if (-EPS < dx && dx < EPS
+	&&  -EPS < dy && dy < EPS
+	&&  -EPS < dz && dz < EPS)
+		return 1;
+
+	return 0;
+}
+
+
+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 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);
+
+	// worst case -- all separate polygons
+	poly_t * const polys = calloc(num_triangles, sizeof(*polys));
+
+	// Collapse coplanar triangles into larger polygons
+	v3_t * const vertices = calloc(num_triangles, 3);
+	int num_vertices = 0;
+
+	for(int i = 0 ; i < num_triangles ; i++)
+	{
+		// see if this matches an existing vertex
+		const stl_face_t * const t = &faces[i];
+		poly_t * const p = &polys[i];
+		p->n = 3;
+		p->p[0] = p->p[1] = p->p[2] = -1;
+
+		for (int j = 0 ; j < num_vertices ; j++)
+		{
+			const v3_t * const v = &vertices[j];
+			if (p->p[0] == -1 && v3_eq(v, &t->p0))
+				p->p[1] = j;
+			if (p->p[1] == -1 && v3_eq(v, &t->p1))
+				p->p[1] = j;
+			if (p->p[2] == -1 && v3_eq(v, &t->p2))
+				p->p[2] = j;
+
+			// check if we've found all of them
+			if (p->p[0] >= 0 && p->p[1] >= 0 && p->p[2] >= 0)
+				break;
+		}
+
+		// create new points if we haven't found matches
+		if (p->p[0] < 0)
+		{
+			p->p[0] = num_vertices;
+			vertices[num_vertices++] = t->p0;
+		}
+		if (p->p[1] < 0)
+		{
+			p->p[1] = num_vertices;
+			vertices[num_vertices++] = t->p1;
+		}
+		if (p->p[3] < 0)
+		{
+			p->p[3] = num_vertices;
+			vertices[num_vertices++] = t->p2;
+		}
+	}
+
+	fprintf(stderr, "unique vertices: %d\n", num_vertices);
+
+	return 0;
+}