Properties panel: dont rebuild while user is mid-edit

The 4 Hz binding-value refresh in OnRenderTick was unconditionally
calling UpdatePropertiesPanel() whenever the selected node had any
property binding and the graph had dirty nodes -- which is every
single 250 ms tick on a Clock-driven graph. UpdatePropertiesPanel
calls panel.Children().Clear() then rebuilds the entire control
tree from scratch, which destroys whatever XAML control had keyboard
focus.

Symptom: with a complex graph + playing Clock + a node with bindings
selected, clicking into a TextBox / NumberBox / ComboBox to edit a
property had a < 250 ms window before the rebuild blew away the
focused control. Effective lag on first successful edit:
pseudorandom 0..20+ seconds depending on click timing.

Fix: walk the focused elements parent chain via VisualTreeHelper and
skip the periodic rebuild while any descendant of PropertiesPanel
holds focus. The user-driven rebuild paths (selection change,
property mutation) are unaffected -- they always rebuild.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Spruill-1

MainWindow.RenderTick.cpp

@@ -247,10 +247,18 @@ namespace winrt::ShaderLab::implementation
             // every frame) caused a 4 Hz rebuild of the entire properties
             // panel -- visibly jittering Slider/NumberBox widths as auto-sized
             // controls re-laid out.
+            //
+            // Additional guard: skip the rebuild when any descendant of the
+            // PropertiesPanel currently has keyboard focus (i.e. the user
+            // is mid-edit in a TextBox / NumberBox / dropdown). The clear()
+            // + recreate cycle was destroying the focused control on every
+            // 250 ms tick, making any property whose owner has a bound
+            // sibling effectively un-editable in a Clock-driven graph.
             if (m_selectedNodeId != 0 && m_graph.HasDirtyNodes())
             {
                 auto* selNode = m_graph.FindNode(m_selectedNodeId);
-                if (selNode && !selNode->propertyBindings.empty())
+                if (selNode && !selNode->propertyBindings.empty() &&
+                    !IsPropertiesPanelInteracting())
                     UpdatePropertiesPanel();
             }
             // Refresh MCP activity indicator (dot color fade + tooltip "Xs ago"

MainWindow.xaml.cpp

@@ -2644,6 +2644,31 @@ namespace winrt::ShaderLab::implementation
         args.Handled(true);
     }
 
+    bool MainWindow::IsPropertiesPanelInteracting()
+    {
+        // Walks the focused element's parent chain looking for the
+        // PropertiesPanel StackPanel. If found, the user is mid-edit on
+        // some control inside the panel and a Clear() + recreate would
+        // destroy their in-progress input. Used by the 4 Hz binding-value
+        // refresh on Clock-driven graphs.
+        try
+        {
+            auto root = this->Content().XamlRoot();
+            if (!root) return false;
+            auto focused = winrt::Microsoft::UI::Xaml::Input::FocusManager::GetFocusedElement(root);
+            auto cur = focused.try_as<winrt::Microsoft::UI::Xaml::DependencyObject>();
+            auto target = PropertiesPanel().try_as<winrt::Microsoft::UI::Xaml::DependencyObject>();
+            if (!cur || !target) return false;
+            for (int hops = 0; hops < 64 && cur; ++hops)
+            {
+                if (cur == target) return true;
+                cur = winrt::Microsoft::UI::Xaml::Media::VisualTreeHelper::GetParent(cur);
+            }
+        }
+        catch (...) {}
+        return false;
+    }
+
     void MainWindow::UpdatePropertiesPanel()
     {
         namespace Controls = winrt::Microsoft::UI::Xaml::Controls;

MainWindow.xaml.h

@@ -342,6 +342,11 @@ namespace winrt::ShaderLab::implementation
         D2D1_POINT_2F m_graphPanStart{};
         D2D1_POINT_2F m_graphPanOrigin{};
         void UpdatePropertiesPanel();
+        // True when any descendant of PropertiesPanel currently has keyboard
+        // focus (TextBox cursor, NumberBox edit, dropdown open). Used by the
+        // 4 Hz binding-value refresh path to avoid clobbering an in-progress
+        // edit by Clear() + recreate on the panel.
+        bool IsPropertiesPanelInteracting();
         void ShowCurveEditorDialog(uint32_t nodeId, const std::wstring& propertyKey, std::function<void()> markDirty);
         void AddMathExpressionInput(uint32_t nodeId);
         void RemoveMathExpressionInput(uint32_t nodeId, const std::wstring& paramName);