From 2448fe26d9523b5d9dca9b7818bd726f8d4901b5 Mon Sep 17 00:00:00 2001
From: Justin Lin <caterpillar@openhome.cc>
Date: Wed, 26 Feb 2020 13:43:39 +0800
Subject: [PATCH] should sort by xy

---
 src/experimental/_impl/_convex_hull_impl.scad | 13 +++++++++++++
 src/experimental/convex_hull.scad             |  3 +--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/experimental/_impl/_convex_hull_impl.scad b/src/experimental/_impl/_convex_hull_impl.scad
index 5d95d9b0..691fd5b7 100644
--- a/src/experimental/_impl/_convex_hull_impl.scad
+++ b/src/experimental/_impl/_convex_hull_impl.scad
@@ -1,5 +1,18 @@
 use <util/slice.scad>;
 
+function _convex_hull_lt_than_by_xy(p1, p2) =
+    p1[0] < p2[0] || (p1[0] == p2[0] && p1[1] < p2[1]);
+
+function _convex_hull_sort_by_xy(lt) = 
+    let(leng = len(lt))
+    leng <= 1 ? lt : 
+        let(
+            pivot = lt[0],
+            before = [for(j = 1; j < leng; j = j + 1) if(_convex_hull_lt_than_by_xy(lt[j], pivot)) lt[j]],
+            after =  [for(j = 1; j < leng; j = j + 1) if(!_convex_hull_lt_than_by_xy(lt[j], pivot)) lt[j]]
+        )
+        concat(_convex_hull_sort_by_xy(before), [pivot], _convex_hull_sort_by_xy(after));
+
 // oa->ob ct_clk : greater than 0
 function _convex_hull_impl_dir(o, a, b) =
     let(
diff --git a/src/experimental/convex_hull.scad b/src/experimental/convex_hull.scad
index dda0bc55..23d83d74 100644
--- a/src/experimental/convex_hull.scad
+++ b/src/experimental/convex_hull.scad
@@ -1,9 +1,8 @@
 use <experimental/_impl/_convex_hull_impl.scad>;
-use <util/sort.scad>;
 
 function convex_hull(points) = 
     let(
-        sorted = sort(points, by = "x"),
+        sorted = _convex_hull_sort_by_xy(points),
         leng = len(sorted),
         lwr_ch = _convex_hull_lower_chain(sorted, leng, [], 0, 0),
         leng_lwr_ch = len(lwr_ch),