Separate out state for new_frame() into a local variable

terminaldisplay.hpp

@@ -4,22 +4,29 @@
 #include "terminalframebuffer.hpp"
 
 namespace Terminal {
+  /* variables used within a new_frame */
+  class FrameState {
+  public:
+    int x, y;
+    std::string str;
+
+    FrameState() : x(0), y(0), str() {}
+    void append( std::string s ) { str.append( s ); }
+  };
+
   class Display {
   private:
     bool initialized;
     Framebuffer last_frame;
     std::string current_rendition_string;
     int cursor_x, cursor_y;
-    int x, y;
-    std::string str;
 
-    void put_cell( Framebuffer &f );
+    void put_cell( FrameState &frame, Framebuffer &f );
 
   public:
     Display( int width, int height )
       : initialized( false ), last_frame( width, height ),
-	current_rendition_string(), cursor_x( -1 ), cursor_y( -1 ),
-	x( 0 ), y( 0 ), str( "" )
+	current_rendition_string(), cursor_x( -1 ), cursor_y( -1 )
     {}
 
     std::string new_frame( Framebuffer &f );