Never use SDL mouse move event data when mouse is hidden and being recentered, as that causes RELATIVE mode to return wrong mouse deltas on OSX.

Source/Urho3D/Input/Input.cpp

@@ -360,7 +360,7 @@ void Input::Update()
     #endif
 
     // Check for relative mode mouse move
-    if (!touchEmulation_ && mouseMode_ != MM_RELATIVE && (graphics_->GetExternalWindow() || (!mouseVisible_ && inputFocus_ && (flags & SDL_WINDOW_MOUSE_FOCUS))))
+    if (!touchEmulation_ && (graphics_->GetExternalWindow() || (!mouseVisible_ && inputFocus_ && (flags & SDL_WINDOW_MOUSE_FOCUS))))
     {
         IntVector2 mousePosition = GetMousePosition();
         mouseMove_ = mousePosition - lastMousePosition_;
@@ -407,21 +407,6 @@ void Input::Update()
             }
         }
     }
-
-    #ifndef EMSCRIPTEN
-    if (mouseMode_ == MM_RELATIVE)
-    {
-        IntVector2 mousePosition = GetMousePosition();
-        IntVector2 center(graphics_->GetWidth() / 2, graphics_->GetHeight() / 2);
-        if (graphics_->GetExternalWindow())
-            lastMousePosition_ = mousePosition;
-        else if (mousePosition != center)
-        {
-            SetMousePosition(center);
-            lastMousePosition_ = center;
-        }
-    }
-    #endif
 }
 
 void Input::SetMouseVisible(bool enable, bool suppressEvent)
@@ -1578,7 +1563,7 @@ void Input::HandleSDLEvent(void* sdlEvent)
         break;
 
     case SDL_MOUSEMOTION:
-        if ((mouseVisible_ || mouseMode_ == MM_RELATIVE) && !touchEmulation_)
+        if (mouseVisible_ && !touchEmulation_)
         {
             mouseMove_.x_ += evt.motion.xrel;
             mouseMove_.y_ += evt.motion.yrel;