diff --git a/libsrc/include/nginterface.h b/libsrc/include/nginterface.h
index 71adea2f..7e71cea7 100644
--- a/libsrc/include/nginterface.h
+++ b/libsrc/include/nginterface.h
@@ -324,7 +324,7 @@ extern "C" {
   /// delete gridfunctions
   DLL_HEADER void Ng_ClearSolutionData();
   // redraw 
-  DLL_HEADER void Ng_Redraw();
+  DLL_HEADER void Ng_Redraw(bool blocking = false);
   ///
   DLL_HEADER void Ng_SetMouseEventHandler (netgen::MouseEventHandler * handler);
   ///
diff --git a/libsrc/meshing/meshtype.hpp b/libsrc/meshing/meshtype.hpp
index f3c340c2..2aca460c 100644
--- a/libsrc/meshing/meshtype.hpp
+++ b/libsrc/meshing/meshtype.hpp
@@ -1110,11 +1110,11 @@ namespace netgen
     // void CopyFrom(const MeshingParameters & other);
     
 
-    void (*render_function)() = NULL;
-    void Render()
+    void (*render_function)(bool) = NULL;
+    void Render(bool blocking = false)
     {
       if (render_function) 
-        (*render_function)();
+        (*render_function)(blocking);
     }
   };
 
diff --git a/libsrc/visualization/mvdraw.cpp b/libsrc/visualization/mvdraw.cpp
index 3975585b..5a8d934f 100644
--- a/libsrc/visualization/mvdraw.cpp
+++ b/libsrc/visualization/mvdraw.cpp
@@ -112,10 +112,16 @@ namespace netgen
   }
 
 
-  extern DLL_HEADER void Render();
-  DLL_HEADER void Render ()
+  extern DLL_HEADER void Render(bool blocking);
+  DLL_HEADER void Render (bool blocking)
   {
-    multithread.redraw = 1;
+    if (blocking)
+      {
+        multithread.redraw = 2;
+        while (multithread.redraw == 2) ; 
+      }
+    else
+      multithread.redraw = 1;
   }
 
 
diff --git a/libsrc/visualization/vssolution.cpp b/libsrc/visualization/vssolution.cpp
index 496155a6..c39341f7 100644
--- a/libsrc/visualization/vssolution.cpp
+++ b/libsrc/visualization/vssolution.cpp
@@ -4609,14 +4609,14 @@ void Ng_SetSolutionData (Ng_SolutionData * soldata)
 
 namespace netgen
 {
-  extern void Render ();
+  extern void Render (bool blocking);
 }
 
-void Ng_Redraw ()
+void Ng_Redraw (bool blocking)
 {
 #ifdef OPENGL
   netgen::vssolution.UpdateSolutionTimeStamp();
-  netgen::Render();
+  netgen::Render(blocking);
 #endif
 }
 
diff --git a/ng/menustat.tcl b/ng/menustat.tcl
index e71efd06..54155f69 100644
--- a/ng/menustat.tcl
+++ b/ng/menustat.tcl
@@ -971,6 +971,7 @@ proc timer2 { } {
     Ng_ReadStatus 
 
     if { $multithread_redraw == 1 } {
+        # non-blocking redraw
 	set multithread_redraw 0;
 	redraw;
         
@@ -980,6 +981,20 @@ proc timer2 { } {
             .ndraw Ng_VideoClip addframe
         }
     }
+    if { $multithread_redraw == 2 } {
+        # blocking redraw
+	redraw;
+	set multithread_redraw 0;
+        
+        global videoactive
+        if { $videoactive == 1 } {
+            puts "addframe"
+            .ndraw Ng_VideoClip addframe
+        }
+        after 1 { timer2 }
+        return
+    }
+
 
     # global mem_moveable
     # set mem_moveable [Ng_MemInfo moveable]
diff --git a/ng/ngpkg.cpp b/ng/ngpkg.cpp
index 08e2ac5a..2f5afa54 100644
--- a/ng/ngpkg.cpp
+++ b/ng/ngpkg.cpp
@@ -1364,7 +1364,7 @@ namespace netgen
     multithread.running = 1;
     multithread.terminate = 0;
     
-    extern void Render();
+    extern void Render(bool blocking);
     mparam.render_function = &Render;
 
     for (int i = 0; i < geometryregister.Size(); i++)