Added ansi_show_unknown(bool) (default off)

It may be useful to some to have the terminal emit an error character
to show unknown escape sequences. Off by default, unknown escape sequences
are silently ignored. If enabled, '¿' is inserted instead.

FL/Fl_Simple_Terminal.H

@@ -161,7 +161,6 @@ private:
 private:
   int  history_lines_;      // max lines allowed in screen history
   bool stay_at_bottom_;     // lets scroller chase last line in buffer
-  bool ansi_;               // enables ANSI sequences
   // scroll management
   int  lines_;              // #lines in buffer (optimization: Fl_Text_Buffer slow to calc this)
   bool scrollaway_;         // true when user changed vscroll away from bottom
@@ -175,7 +174,10 @@ private:
   int  normal_style_index_;  // "normal" style used by "\033[0m" reset sequence
   int  current_style_index_; // current style used for drawing text
   char current_style_;       // current 'style char' (e.g. 'A' = first style entry)
+  // ANSI escape seq
   Fl_Escape_Seq escseq;      // escape sequence state handler
+  bool ansi_;                // enables ANSI sequences
+  bool ansi_show_unknown_;   // show '¿' for unknown ESC sequences (default: off)
   // String parsing vars initialized/used by append(), used by handle_backspace() etc.
   char *ntm_;                // new text memory  (ntm) - malloc()ed by append() for output text
   char *ntp_;                // new text ptr     (ntp) - points into ntm buffer
@@ -193,6 +195,8 @@ public:
   int  history_lines() const;
   void ansi(bool val);
   bool ansi() const;
+  void ansi_show_unknown(bool val);
+  bool ansi_show_unknown() const;
   void style_table(Fl_Text_Display::Style_Table_Entry *stable, int stable_size, int normal_style_index=0);
   const Fl_Text_Display::Style_Table_Entry *style_table() const;
   int style_table_size() const;
@@ -234,6 +238,7 @@ protected:
   void backspace_buffer(unsigned int count);
   void handle_backspace();
   void append_ansi(const char *s, int len);
+  void unknown_escape();
 };
 
 #endif

src/Fl_Simple_Terminal.cxx

@@ -287,7 +287,6 @@ void Fl_Simple_Terminal::vscroll_cb(Fl_Widget *w, void *data) {
 Fl_Simple_Terminal::Fl_Simple_Terminal(int X,int Y,int W,int H,const char *l) : Fl_Text_Display(X,Y,W,H,l) {
   history_lines_ = 500;         // something 'reasonable'
   stay_at_bottom_ = true;
-  ansi_ = false;
   lines_ = 0;                    // note: lines!=mNBufferLines when lines are wrapping
   scrollaway_ = false;
   scrolling_ = false;
@@ -312,6 +311,9 @@ Fl_Simple_Terminal::Fl_Simple_Terminal(int X,int Y,int W,int H,const char *l) :
   normal_style_index_  = builtin_normal_index;
   current_style_index_ = builtin_normal_index;
   current_style_       = 'A' + 0;
+  // ANSI escape seq
+  ansi_ = false;
+  ansi_show_unknown_ = false;
   // Intercept vertical scrolling
   orig_vscroll_cb_     = mVScrollBar->callback();
   orig_vscroll_data_   = mVScrollBar->user_data();
@@ -470,6 +472,23 @@ void Fl_Simple_Terminal::ansi(bool val) {
   redraw();
 }
 
+/**
+ See if we should show unknown ANSI sequences with '¿' or not.
+ \see ansi_show_unknown(bool)
+*/
+bool Fl_Simple_Terminal::ansi_show_unknown(void) const {
+  return ansi_show_unknown_;
+}
+
+/**
+ Enable showing unknown ESC sequences with the '¿' character.
+ By default this is off, and unknown escape sequences are silently ignored.
+ \see ansi_show_unknown()
+*/
+void Fl_Simple_Terminal::ansi_show_unknown(bool val) {
+  ansi_show_unknown_ = val;
+}
+
 /**
  Return the current style table being used.
 
@@ -760,6 +779,16 @@ void Fl_Simple_Terminal::handle_backspace() {
   backspace_buffer(1);
 } 
 
+// Handle unknown esc sequences
+void Fl_Simple_Terminal::unknown_escape() {
+  if ( ansi_show_unknown() ) {
+    for ( const char *s = "¿"; *s; s++ ) {
+      *ntp_++ = *s;                        // emit utf-8 encoded char
+      *nsp_++ = current_style();           // use current style
+    }
+  }
+}
+
 /**
  Handle appending string with ANSI escape sequences, and other 'special'
  character processing (such as backspaces).
@@ -782,6 +811,7 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
       if ( escseq.parse_in_progress() ) {   // ESC sequence in progress?
         switch ( escseq.parse(*sp) ) {      // parse until completed or fail
           case Fl_Escape_Seq::fail:         // parsing error?
+            unknown_escape();
             escseq.reset();                 // ..reset and continue
             ++sp;
             continue;
@@ -801,10 +831,10 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
             case 'J':                       // ESC[#J
               switch (val) {
                 case 0:                     // ESC[0J -- clear to eol
-                  // unsupported
+                  unknown_escape();
                   break;
                 case 1:                     // ESC[1J -- clear to sol
-                  // unsupported
+                  unknown_escape();
                   break;
                 case 2:                     // ESC[2J -- clear visible screen
                   // NOTE: Currently we clear the /entire screen history/, and
@@ -817,6 +847,9 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
                   ntp_ = ntm_;              // clear text contents accumulated so far
                   nsp_ = nsm_;              // clear style contents ""
                   break;
+                default:                    // all other ESC[#J unsupported
+                  unknown_escape();
+                  break;
               }
               break;
             // SELECT GRAPHIC RENDITION (SGR)
@@ -831,6 +864,7 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
               break;
             // UNSUPPORTED MODES
             default:
+              unknown_escape();
               break;                         // unsupported
           }
         }