From 6a1b141d5c62dd692620f12efb9791f11d88a3c9 Mon Sep 17 00:00:00 2001
From: Adrian Mariano <avm4@cornell.edu>
Date: Fri, 5 Mar 2021 20:39:15 -0500
Subject: [PATCH] hull 2d tweak

---
 hull.scad            | 18 +++++++++---------
 tests/test_hull.scad |  8 ++++----
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/hull.scad b/hull.scad
index fbfecdb..5658bec 100644
--- a/hull.scad
+++ b/hull.scad
@@ -80,7 +80,7 @@ function _backtracking(i,points,h,t,m) =
     _backtracking(i,points,h,t,m-1) ;
 
 // clockwise check (2d)
-function _is_cw(a,b,c) = cross(a-c,b-c)<=0;
+function _is_cw(a,b,c) = cross(a-c,b-c)<-EPSILON*norm(a-c)*norm(b-c);
 
 
 // Function: hull2d_path()
@@ -100,13 +100,7 @@ function _is_cw(a,b,c) = cross(a-c,b-c)<=0;
 //
 function hull2d_path(points) =
     assert(is_path(points,2),"Invalid input to hull2d_path")
-    len(points) < 2 ? []
-  : len(points) == 2 ? [0,1]
-  : let(tri=noncollinear_triple(points, error=false))
-    tri == [] ? _hull_collinear(points)
-  :
-    assert(is_path(points,2))
-    assert(len(points)>=3, "Point list must contain at least 3 points.")
+    len(points) < 2 ? [] :
     let( n  = len(points), 
          ip = sortidx(points) )
     // lower hull points
@@ -134,13 +128,19 @@ function hull2d_path(points) =
 function _hull_collinear(points) =
     let(
         a = points[0],
-        n = points[1] - a,
+        i = max_index([for(pt=points) norm(pt-a)]),
+        n = points[i] - a
+    )
+    norm(n)==0 ? [0]
+    :
+    let(
         points1d = [ for(p = points) (p-a)*n ],
         min_i = min_index(points1d),
         max_i = max_index(points1d)
     ) [min_i, max_i];
 
 
+
 // Function: hull3d_faces()
 // Usage:
 //   hull3d_faces(points)
diff --git a/tests/test_hull.scad b/tests/test_hull.scad
index 3aba71a..a6a7926 100644
--- a/tests/test_hull.scad
+++ b/tests/test_hull.scad
@@ -6,9 +6,9 @@ module test_hull() {
     assert_equal(hull([[3,4,1],[5,5,3]]), [0,1]);
 
     test_collinear_2d = let(u = unit([5,3]))    [ for(i = [9,2,3,4,5,7,12,15,13]) i * u ];
-    assert_equal(hull(test_collinear_2d), [7,1]);
+    assert_equal(sort(hull(test_collinear_2d)), [1,7]);
     test_collinear_3d = let(u = unit([5,3,2]))    [ for(i = [9,2,3,4,5,7,12,15,13]) i * u ];
-    assert_equal(hull(test_collinear_3d), [7,1]);
+    assert_equal(sort(hull(test_collinear_3d)), [1,7]);
 
     /*    // produces some extra points along edges
     test_square_2d = [for(x=[1:5], y=[2:6]) [x,y]];
@@ -105,9 +105,9 @@ module test_hull2d_path() {
     assert_equal(hull([[3,4,1],[5,5,3]]), [0,1]);
 
     test_collinear_2d = let(u = unit([5,3]))    [ for(i = [9,2,3,4,5,7,12,15,13]) i * u ];
-    assert_equal(hull(test_collinear_2d), [7,1]);
+    assert_equal(sort(hull(test_collinear_2d)), [1,7]);
     test_collinear_3d = let(u = unit([5,3,2]))    [ for(i = [9,2,3,4,5,7,12,15,13]) i * u ];
-    assert_equal(hull(test_collinear_3d), [7,1]);
+    assert_equal(sort(hull(test_collinear_3d)), [1,7]);
 
     rand10_2d = [[1.55356, -1.98965], [4.23157, -0.947788], [-4.06193, -1.55463],
                  [1.23889, -3.73133], [-1.02637, -4.0155], [4.26806, -4.61909],