From 60e38e67718890d4a64cf4009cf66597abd3f4d1 Mon Sep 17 00:00:00 2001
From: Dabinn <dabinn@gmail.com>
Date: Thu, 12 Mar 2020 10:44:37 +0800
Subject: [PATCH] Keep Model Upright when Rotating

---
 open3mod/OrbitCameraController.cs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/open3mod/OrbitCameraController.cs b/open3mod/OrbitCameraController.cs
index f083acc..2e500b5 100644
--- a/open3mod/OrbitCameraController.cs
+++ b/open3mod/OrbitCameraController.cs
@@ -96,7 +96,11 @@ public void MouseMove(int x, int y)
 
             if (x != 0)
             {
-                _view *= Matrix4.CreateFromAxisAngle(_up, (float)(x * RotationSpeed * Math.PI / 180.0));
+                // Free Orbit
+                //_view *= Matrix4.CreateFromAxisAngle(_up, (float)(x * RotationSpeed * Math.PI / 180.0));
+                
+                // Constrained Orbit: Keep Model Upright when Rotating
+                _view *= Matrix4.CreateFromAxisAngle(Matrix4.Invert(_view).Column1.Xyz, (float)(x * RotationSpeed * Math.PI / 180.0));
             }
 
             if (y != 0)