From 482a6958a758fbe3427a09d652c5511a4a799efc Mon Sep 17 00:00:00 2001
From: Viktor Kovacs <viktorkovacs@gmail.com>
Date: Sun, 25 Apr 2021 19:52:33 +0200
Subject: [PATCH] Flip triangles when the model should be mirrored.

---
 source/import/importer3ds.js |  8 ++++++--
 source/model/modelutils.js   | 10 ++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/source/import/importer3ds.js b/source/import/importer3ds.js
index 2ea3236..aa9ffae 100644
--- a/source/import/importer3ds.js
+++ b/source/import/importer3ds.js
@@ -504,8 +504,10 @@ OV.Importer3ds = class extends OV.ImporterBase
                 nodeMatrix = GetNodeTransformation (nodeHierarchy, node);
             }
 
+            let mesh = model.GetMesh (currentMeshIndex);
             let determinant = meshMatrix.Determinant ();
-            if (OV.IsNegative (determinant)) {
+            let mirrorByX = OV.IsNegative (determinant);
+            if (mirrorByX) {
                 // Mirror by x coordinates
                 let scaleMatrix = new OV.Matrix ().CreateScale (-1.0, 1.0, 1.0);
                 meshMatrix = scaleMatrix.MultiplyMatrix (meshMatrix);
@@ -524,7 +526,9 @@ OV.Importer3ds = class extends OV.ImporterBase
             matrix = invMeshMatrix.MultiplyMatrix (matrix);
 
             let transformation = new OV.Transformation (matrix);
-            let mesh = model.GetMesh (currentMeshIndex);
+            if (mirrorByX) {
+                OV.FlipMeshTrianglesOrientation (mesh);
+            }
             OV.TransformMesh (mesh, transformation);
         }
 
diff --git a/source/model/modelutils.js b/source/model/modelutils.js
index 9e6a137..1d9f09a 100644
--- a/source/model/modelutils.js
+++ b/source/model/modelutils.js
@@ -41,6 +41,16 @@ OV.TransformMesh = function (mesh, transformation)
     }
 };
 
+OV.FlipMeshTrianglesOrientation = function (mesh)
+{
+    for (let i = 0; i < mesh.TriangleCount (); i++) {
+        let triangle = mesh.GetTriangle (i);
+        let tmp = triangle.v1;
+        triangle.v1 = triangle.v2;
+        triangle.v2 = tmp;
+    }
+};
+
 OV.GetMeshBoundingBox = function (mesh)
 {
     let min = new OV.Coord3D (Infinity, Infinity, Infinity);