Hopefully a workaround for crashes and hang ups at closing on Windows.

Release the OpenGL contexts not by a destructor of a static class,
but explicitely (predictively).

src/PrusaSlicer.cpp

@@ -48,6 +48,7 @@
 #ifdef SLIC3R_GUI
     #include "slic3r/GUI/GUI.hpp"
     #include "slic3r/GUI/GUI_App.hpp"
+    #include "slic3r/GUI/3DScene.hpp"
 #endif /* SLIC3R_GUI */
 
 using namespace Slic3r;
@@ -505,7 +506,10 @@ int CLI::run(int argc, char **argv)
             if (! m_extra_config.empty())
                 gui->mainframe->load_config(m_extra_config);
         });
-        return wxEntry(argc, argv);
+        int result = wxEntry(argc, argv);
+        //FIXME this is a workaround for the PrusaSlicer 2.1 release.
+		_3DScene::destroy();
+        return result;
 #else /* SLIC3R_GUI */
         // No GUI support. Just print out a help.
         this->print_help(false);

src/slic3r/GUI/3DScene.cpp

@@ -2007,6 +2007,11 @@ bool _3DScene::init(wxGLCanvas* canvas)
     return s_canvas_mgr.init(canvas);
 }
 
+void _3DScene::destroy()
+{
+    s_canvas_mgr.destroy();
+}
+
 GUI::GLCanvas3D* _3DScene::get_canvas(wxGLCanvas* canvas)
 {
     return s_canvas_mgr.get_canvas(canvas);

src/slic3r/GUI/3DScene.hpp

@@ -647,6 +647,7 @@ public:
     static void remove_all_canvases();
 
     static bool init(wxGLCanvas* canvas);
+    static void destroy();
 
     static GUI::GLCanvas3D* get_canvas(wxGLCanvas* canvas);
 

src/slic3r/GUI/GLCanvas3DManager.cpp

@@ -197,11 +197,7 @@ GLCanvas3DManager::GLCanvas3DManager()
 
 GLCanvas3DManager::~GLCanvas3DManager()
 {
-    if (m_context != nullptr)
+	this->destroy();
-    {
-        delete m_context;
-        m_context = nullptr;
-    }
 }
 
 bool GLCanvas3DManager::add(wxGLCanvas* canvas, Bed3D& bed, Camera& camera, GLToolbar& view_toolbar)
@@ -282,6 +278,15 @@ bool GLCanvas3DManager::init(wxGLCanvas* canvas)
         return false;
 }
 
+void GLCanvas3DManager::destroy()
+{
+    if (m_context != nullptr)
+    {
+        delete m_context;
+        m_context = nullptr;
+    }
+}
+
 GLCanvas3D* GLCanvas3DManager::get_canvas(wxGLCanvas* canvas)
 {
     CanvasesMap::const_iterator it = do_get_canvas(canvas);

src/slic3r/GUI/GLCanvas3DManager.hpp

@@ -91,6 +91,7 @@ public:
     void init_gl();
 
     bool init(wxGLCanvas* canvas);
+    void destroy();
 
     GLCanvas3D* get_canvas(wxGLCanvas* canvas);