From 1bb8df69a917f0102dbe96370a46a5d02cb19709 Mon Sep 17 00:00:00 2001
From: Keith Winstein <keithw@mit.edu>
Date: Thu, 13 Oct 2011 15:37:26 -0400
Subject: [PATCH] Only flag (underline) predictions on long echo delay

---
 terminaloverlay.cpp | 8 +++++++-
 terminaloverlay.hpp | 7 +++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/terminaloverlay.cpp b/terminaloverlay.cpp
index 71f54d8..efaa10d 100644
--- a/terminaloverlay.cpp
+++ b/terminaloverlay.cpp
@@ -22,7 +22,9 @@ void OverlayCell::apply( Framebuffer &fb ) const
 
   if ( !(*(fb.get_mutable_cell( row, col )) == replacement) ) {
     *(fb.get_mutable_cell( row, col )) = replacement;
-    fb.get_mutable_cell( row, col )->renditions.bold = true; /* XXX */
+    if ( flag ) {
+      fb.get_mutable_cell( row, col )->renditions.underlined = true;
+    }
   }
 }
 
@@ -122,6 +124,9 @@ void PredictionEngine::cull( const Framebuffer &fb )
       i++;
     }
   }
+
+  if ( SRTT > 150 ) flagging = true; /* start underlining predicted chars */
+  if ( SRTT < 100 ) flagging = false; /* use some hysterisis to avoid annoying flicker */
 }
 
 OverlayCell::OverlayCell( uint64_t expiration_time, int s_row, int s_col, int background_color )
@@ -342,6 +347,7 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
     coc->replacement = *existing_cell;
     coc->replacement.contents.clear();
     coc->replacement.contents.push_back( the_byte );
+    coc->flag = flagging;
 
     ccm->new_col++;
     ccm->expiration_time = now + prediction_len();
diff --git a/terminaloverlay.hpp b/terminaloverlay.hpp
index d1f0be0..95fd592 100644
--- a/terminaloverlay.hpp
+++ b/terminaloverlay.hpp
@@ -21,12 +21,14 @@ namespace Overlay {
   class OverlayElement {
   public:
     uint64_t prediction_time, expiration_time;
+    bool flag; /* whether to bold for the user */
 
     virtual void apply( Framebuffer &fb ) const = 0;
     virtual Validity get_validity( const Framebuffer & ) const;
 
     OverlayElement( uint64_t s_expiration_time ) : prediction_time( timestamp() ),
-						   expiration_time( s_expiration_time ) {}
+						   expiration_time( s_expiration_time ),
+						   flag( false ) {}
     virtual ~OverlayElement() {}
   };
 
@@ -112,6 +114,7 @@ namespace Overlay {
     /* use the TCP timeout algorithm to measure appropriate echo prediction timeout */
     bool RTT_hit;
     double SRTT, RTTVAR;
+    bool flagging;
     int prediction_len( void );
 
   public:
@@ -119,7 +122,7 @@ namespace Overlay {
     void new_user_byte( char the_byte, const Framebuffer &fb );
     void calculate_score( const Framebuffer &fb );
 
-    PredictionEngine() : score( 0 ), RTT_hit( false ), SRTT( 1000 ), RTTVAR( 500 ) {}
+    PredictionEngine() : score( 0 ), RTT_hit( false ), SRTT( 1000 ), RTTVAR( 500 ), flagging( false ) {}
 
     int get_score( void ) { return score; }
   };