Correctly render on terminals without BCE (fixes #56 github issue)

src/terminal/terminaldisplay.cc

@@ -244,12 +244,15 @@ void Display::put_cell( bool initialized, FrameState &frame, const Framebuffer &
 
     assert( frame.x + clear_count <= f.ds.get_width() );
 
+    bool can_use_erase = has_bce || (cell->renditions == initial_rendition());
+
     /* can we go to the end of the line? */
-    if ( frame.x + clear_count == f.ds.get_width() ) {
+    if ( (frame.x + clear_count == f.ds.get_width())
+	 && can_use_erase ) {
       frame.append( "\033[K" );
       frame.x += clear_count;
     } else {
-      if ( has_ech ) {
+      if ( has_ech && can_use_erase ) {
 	if ( clear_count == 1 ) {
 	  frame.append( "\033[X" );
 	} else {
@@ -258,6 +261,7 @@ void Display::put_cell( bool initialized, FrameState &frame, const Framebuffer &
 	}
 	frame.x += clear_count;
       } else { /* no ECH, so just print a space */
+	/* unlike erases, this will use background color irrespective of BCE */
 	frame.append( " " );
 	frame.cursor_x++;
 	frame.x++;

src/terminal/terminaldisplay.h

@@ -52,6 +52,8 @@ namespace Terminal {
     bool has_ech; /* erase character is part of vt200 but not supported by tmux
 		     (or by "screen" terminfo entry, which is what tmux advertises) */
 
+    bool has_bce; /* erases result in cell filled with background color */
+
     void put_cell( bool initialized, FrameState &frame, const Framebuffer &f ) const;
 
   public:

src/terminal/terminaldisplayinit.cc

@@ -29,7 +29,7 @@
 using namespace Terminal;
 
 Display::Display( bool use_environment )
-  : has_ech( true )
+  : has_ech( true ), has_bce( true )
 {
   if ( use_environment ) {
     int errret = -2;
@@ -52,12 +52,24 @@ Display::Display( bool use_environment )
       } 
     }
 
+    /* check for ECH */
     char ech_name[] = "ech";
     char *val = tigetstr( ech_name );
-    if ( val == (char *)-1 )
+    if ( val == (char *)-1 ) {
       throw std::string( "Invalid terminfo string capability " ) + ech_name;
+    }
     if ( val == 0 ) {
       has_ech = false;
     }
+
+    /* check for BCE */
+    char bce_name[] = "bce";
+    int bce_val = tigetflag( bce_name );
+    if ( bce_val == -1 ) {
+      throw std::string( "Invalid terminfo boolean capability " ) + bce_name;
+    }
+    if ( bce_val == 0 ) {
+      has_bce = false;
+    }
   }
 }