From bbe27d79cac5c8406b69041f56588bfe0b642734 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Sun, 5 Nov 2017 19:09:16 +0000
Subject: [PATCH] wip pins

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 genscad           | 44 +++++++++++++++++++++++++++++++++++++++++++-
 moebius-demo.scad | 10 ++++++++++
 2 files changed, 53 insertions(+), 1 deletion(-)

diff --git a/genscad b/genscad
index b2b83bf..26814fe 100755
--- a/genscad
+++ b/genscad
@@ -10,6 +10,8 @@ from moebius import *
 nomsize = 20
 thick = 1.0
 
+sliceat = 1.675;
+
 nv = 80
 nw = 80
 
@@ -74,6 +76,46 @@ def make_moebius(objname):
           for b in (-1, +1) ])
   so.writeout(objname, nomsize)
 
-make_moebius('MoebiusCore')
+def make_pinlocations():
+  bests = [ None, None ] # bests[ y>=0 ] = (locn, normal)
 
+  def goodness(info):
+    # we find the one with biggest Z (actually, the least -ve)
+    return (
+      0 * np.linalg.norm(info[0][0:2])
+      -abs(info[1][2])
+    )
+    return abs(info[1][1])
+
+  for v in range(0, nv):
+    for w in range(0, nw):
+      core_quad = [ m.point(v+a, w+b)
+                    for a in (1, 0)
+                    for b in (1, 0) ]
+      for p,q in [ (core_quad[i], core_quad[(i+1) % 4])
+                   for i in range(0,4) ]:
+        normal = (m.point_offset(v,  w,   0.5) - core_quad[0] +
+                  m.point_offset(v+1,w+1, 0.5) - core_quad[3]);
+        if normal[2] > 0: # inwards, make outwards
+          normal = -normal
+
+        #print(repr((p,q)), file=sys.stderr)
+        if (p[2] > -sliceat) == (q[2] > -sliceat): continue
+
+        lincomb = (-sliceat - p[2]) / (q[2] - p[2])
+        here = p * (1-lincomb) + q * lincomb;
+        best_key = here[1] >= 0
+        prospective = (here,normal)
+        if (bests[best_key] is None or
+            goodness(prospective) > goodness(bests[best_key])):
+          bests[best_key] = prospective
+  def print_bests(name, info_index):
+    print('moebius_pin_%s=[' % name)
+    for b in bests: print(repr(list(b[info_index])),',')
+    print('];')
+  print_bests('locns', 0)
+  print_bests('normals', 1)
+
+make_moebius('MoebiusCore')
+make_pinlocations()
 print('moebiuscore_nomsize=%s;' % repr(nomsize))
diff --git a/moebius-demo.scad b/moebius-demo.scad
index 9d99c56..1b2c6ff 100644
--- a/moebius-demo.scad
+++ b/moebius-demo.scad
@@ -9,3 +9,13 @@ intersection(){
   translate([0,0, 200-sliceat])
     cube(center=true, 400);
 }
+
+%for (i=[0,1]) {
+  hull(){
+    translate( moebius_pin_locns[i] * moebiuscore_nomsize )
+      sphere(2 + i);
+    translate( moebius_pin_locns[i] * moebiuscore_nomsize +
+	       moebius_pin_normals[i] * moebiuscore_nomsize*0.5 )
+      sphere(2 + i);
+  }
+}
-- 
2.30.2