fix M_dual

panda/src/pgraph/cullResult.cxx

@@ -140,7 +140,7 @@ add_object(CullableObject *object, const CullTraverser *traverser) {
 #ifndef NDEBUG
       check_flash_transparency(object->_state, flash_dual_color);
 #endif
-      if (m_dual) {
+      if (!m_dual) {
         // If m_dual is configured off, it becomes M_alpha.
         break;
       }