From 640814fdf67dc83a97a387522b939da45ec77709 Mon Sep 17 00:00:00 2001
From: AJ Isaacs <ajisaacs27@gmail.com>
Date: Thu, 9 Apr 2026 10:41:18 -0400
Subject: [PATCH] fix: marshal timer callbacks to UI thread to prevent GDI+
 threading exception

System.Timers.Timer fires on thread pool threads, causing GraphicsPath
objects to be accessed concurrently by hover detection and OnPaint,
triggering "Object is currently in use elsewhere" in DrawParts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 OpenNest/Controls/PlateView.cs | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/OpenNest/Controls/PlateView.cs b/OpenNest/Controls/PlateView.cs
index 1c11ff8..387f781 100644
--- a/OpenNest/Controls/PlateView.cs
+++ b/OpenNest/Controls/PlateView.cs
@@ -621,30 +621,30 @@ namespace OpenNest.Controls
 
         private void redrawTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
         {
-            Invalidate();
+            if (IsDisposed || !IsHandleCreated) return;
+            BeginInvoke(new System.Action(Invalidate));
         }
 
         private void hoverTimer_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
+        {
+            if (IsDisposed || !IsHandleCreated) return;
+            BeginInvoke(new System.Action(HoverCheck));
+        }
+
+        private void HoverCheck()
         {
             var graphPt = PointControlToGraph(hoverPoint);
             LayoutPart hitPart = null;
-            try
+
+            for (var i = parts.Count - 1; i >= 0; --i)
             {
-                for (var i = parts.Count - 1; i >= 0; --i)
+                if (parts[i].Path.GetBounds().Contains(graphPt) &&
+                    parts[i].Path.IsVisible(graphPt))
                 {
-                    if (parts[i].Path.GetBounds().Contains(graphPt) &&
-                        parts[i].Path.IsVisible(graphPt))
-                    {
-                        hitPart = parts[i];
-                        break;
-                    }
+                    hitPart = parts[i];
+                    break;
                 }
             }
-            catch (InvalidOperationException)
-            {
-                // GraphicsPath in use by paint thread — skip this hover tick
-                return;
-            }
 
             hoveredPart = hitPart;
             showTooltip = hitPart != null;