From c80b073e82f2b1a0fb8c61e7ebff547d65df55e1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adam=20Urba=C5=84czyk?=
 <adam-urbanczyk@users.noreply.github.com>
Date: Mon, 3 Aug 2020 16:55:51 +0200
Subject: [PATCH 1/2] Fix tessellate

---
 cadquery/occ_impl/shapes.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cadquery/occ_impl/shapes.py b/cadquery/occ_impl/shapes.py
index 18777b9ca..105cb6dd7 100644
--- a/cadquery/occ_impl/shapes.py
+++ b/cadquery/occ_impl/shapes.py
@@ -822,7 +822,7 @@ def tessellate(
 
             # add triangles
             triangles += [
-                tuple(el + offset for el in t.Get()) for t in poly.Triangles()
+                tuple(el + offset - 1 for el in t.Get()) for t in poly.Triangles()
             ]
 
             offset += poly.NbNodes()

From 5120642ef3a96963a9cc1bff25de38be4cb545c1 Mon Sep 17 00:00:00 2001
From: adam-urbanczyk <adam.jan.urbanczyk@gmail.com>
Date: Tue, 4 Aug 2020 08:54:50 +0200
Subject: [PATCH 2/2] Winding fix

---
 cadquery/occ_impl/shapes.py | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/cadquery/occ_impl/shapes.py b/cadquery/occ_impl/shapes.py
index 105cb6dd7..0f56db781 100644
--- a/cadquery/occ_impl/shapes.py
+++ b/cadquery/occ_impl/shapes.py
@@ -799,13 +799,13 @@ def intersect(self, *toIntersect: "Shape") -> "Shape":
 
     def tessellate(
         self, tolerance: float
-    ) -> Tuple[List[Vector], List[Tuple[int, ...]]]:
+    ) -> Tuple[List[Vector], List[Tuple[int, int, int]]]:
 
         if not BRepTools.Triangulation_s(self.wrapped, tolerance):
             BRepMesh_IncrementalMesh(self.wrapped, tolerance, True)
 
-        vertices = []
-        triangles = []
+        vertices: List[Vector] = []
+        triangles: List[Tuple[int, int, int]] = []
         offset = 0
 
         for f in self.Faces():
@@ -813,6 +813,11 @@ def tessellate(
             loc = TopLoc_Location()
             poly = BRep_Tool.Triangulation_s(f.wrapped, loc)
             Trsf = loc.Transformation()
+            reverse = (
+                True
+                if f.wrapped.Orientation() == TopAbs_Orientation.TopAbs_REVERSED
+                else False
+            )
 
             # add vertices
             vertices += [
@@ -822,7 +827,18 @@ def tessellate(
 
             # add triangles
             triangles += [
-                tuple(el + offset - 1 for el in t.Get()) for t in poly.Triangles()
+                (
+                    t.Value(1) + offset - 1,
+                    t.Value(3) + offset - 1,
+                    t.Value(2) + offset - 1,
+                )
+                if reverse
+                else (
+                    t.Value(1) + offset - 1,
+                    t.Value(2) + offset - 1,
+                    t.Value(3) + offset - 1,
+                )
+                for t in poly.Triangles()
             ]
 
             offset += poly.NbNodes()