A bit of cleanup and testing of the panel, then some optimization to avoid re-rendering and multiple wchar converts.

panel.cpp

@@ -1,24 +1,31 @@
 #include "panel.hpp"
 
 void Panel::resize(int width, int height) {
+  $dirty = true;
   $screen = Screen(width, height);
 }
 
 void Panel::set_renderer(std::function< Element()> render) {
+  $dirty = true;
   $component = Renderer(render);
 }
 
-Screen &Panel::render() {
+void Panel::render() {
+  $dirty = true;
   if($must_clear) $screen.Clear();
   Render($screen, $component->Render());
-  return $screen;
 }
 
-std::wstring Panel::to_string() {
-  std::string screenout = $screen.ToString();
-  return $converter.from_bytes(screenout);
+const std::wstring& Panel::to_string() {
+  if($dirty) {
+    std::string as_text = $screen.ToString();
+    $screenout = $converter.from_bytes(as_text);
+    $dirty = false;
+  }
+
+  return $screenout;
 }
 
-Screen &Panel::screen() {
+const Screen &Panel::screen() {
   return $screen;
 }