From af8e67321597b61a4ce59710bf07d8fee095534d Mon Sep 17 00:00:00 2001
From: Chris Hodapp <hodapp87@gmail.com>
Date: Tue, 24 Sep 2019 04:25:13 +0200
Subject: [PATCH] Write join_boundary_simple

---
 Scratch.ipynb | 18 ++++++++++++++++++
 meshutil.py   | 19 +++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/Scratch.ipynb b/Scratch.ipynb
index ab708c2..007a7a0 100644
--- a/Scratch.ipynb
+++ b/Scratch.ipynb
@@ -12,6 +12,24 @@
     "import trimesh"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": 5,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "b1 = numpy.array([\n",
+    "    [0, 0, 0],\n",
+    "    [1, 0, 0],\n",
+    "    [1, 1, 0],\n",
+    "    [0, 1, 0],\n",
+    "], dtype=numpy.float64)\n",
+    "b2 = numpy.array(b1 + [0,0,1])\n",
+    "\n",
+    "testmesh = meshutil.join_boundary_simple(b1, b2)\n",
+    "testmesh.to_stl_mesh().save(\"simple.stl\")"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": 65,
diff --git a/meshutil.py b/meshutil.py
index a9188fc..24779fe 100644
--- a/meshutil.py
+++ b/meshutil.py
@@ -135,3 +135,22 @@ def cube_distort(angle, open_xz=False):
         faces[11,:] = [0, 5, 4]
         # winding order?
     return FaceVertexMesh(verts, faces)
+
+def join_boundary_simple(bound1, bound2):
+    # bound1 & bound2 are both arrays of shape (N,3), representing
+    # the points of a boundary.  This joins the two boundaries by
+    # simply connecting quads (made of 2 triangles) straight across.
+    #
+    # Winding will proceed in the direction of the first boundary.
+    #`
+    # Returns FaceVertexMesh.
+    n = bound1.shape[0]
+    vs = numpy.concatenate([bound1, bound2])
+    # Indices 0...N-1 are from bound1, N...2*N-1 are from bound2
+    fs = numpy.zeros((2*n, 3), dtype=int)
+    for i in range(n):
+        v0 = i
+        v1 = (i + 1) % n
+        fs[2*i]     = [n + v1, n + v0, v0]
+        fs[2*i + 1] = [v1,     n + v1, v0]
+    return FaceVertexMesh(vs, fs)