Fixed issue #2 - updating parent transformations and accessing child world transform don't return the right result

MonoGameSceneGraph/MonoGameSceneGraph.csproj

@@ -7,7 +7,7 @@
     <ProductVersion>8.0.30703</ProductVersion>
     <SchemaVersion>2.0</SchemaVersion>
     <ProjectGuid>{235539D2-2263-48F3-9DE4-70AE5E335E07}</ProjectGuid>
-    <OutputType>WinExe</OutputType>
+    <OutputType>Library</OutputType>
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>MonoGameSceneGraph</RootNamespace>
     <AssemblyName>MonoGameSceneGraph</AssemblyName>

MonoGameSceneGraph/Source/Nodes/Node.cs

@@ -329,6 +329,22 @@ namespace MonoGameSceneGraph
             _parentLastTransformVersion = newParent != null ? newParent._transformVersion - 1 : 1;
         }
 
+        /// <summary>
+        /// Return true if we need to update world transform due to parent change.
+        /// </summary>
+        private bool NeedUpdateDueToParentChange()
+        {
+            // no parent? if parent last transform version is not 0, it means we had a parent but now we don't. 
+            // still require update.
+            if (_parent == null)
+            {
+                return _parentLastTransformVersion != 0;
+            }
+
+            // check if parent is dirty, or if our last parent transform version mismatch parent current transform version
+            return (_parent._isDirty || _parentLastTransformVersion != _parent._transformVersion);
+        }
+
         /// <summary>
         /// Calc final transformations for current frame.
         /// This uses an indicator to know if an update is needed, so no harm is done if you call it multiple times.
@@ -341,14 +357,19 @@ namespace MonoGameSceneGraph
                 _localTransform = _transformations.BuildMatrix();
             }
             
-            // if local transformations are dirty, or parent transformations are out-of-date, update world transformations
-            if (_isDirty || 
-                (_parent != null && _parentLastTransformVersion != _parent._transformVersion) ||
-                (_parent == null && _parentLastTransformVersion != 0))
+            // if local transformations are dirty or parent transformations are out-of-date, update world transformations
+            if (_isDirty || NeedUpdateDueToParentChange())
             {
                 // if we got parent, apply its transformations
                 if (_parent != null)
                 {
+                    // if parent need update, update it first
+                    if (_parent._isDirty)
+                    {
+                        _parent.UpdateTransformations();
+                    }
+
+                    // recalc world transform
                     _worldTransform = _localTransform * _parent._worldTransform;
                     _parentLastTransformVersion = _parent._transformVersion;
                 }