Filters: add a show line numbers filter

src/filters.cc

@@ -90,4 +90,37 @@ void expand_tabulations(DisplayBuffer& display_buffer)
     }
 }
 
+void show_line_numbers(DisplayBuffer& display_buffer)
+{
+    const Buffer& buffer = display_buffer.front().begin().buffer();
+    BufferCoord coord = buffer.line_and_column_at(display_buffer.begin()->begin());
+
+    int last_line = buffer.line_and_column_at(display_buffer.back().end()-1).line;
+
+    for (; coord.line <= last_line; ++coord.line)
+    {
+        BufferIterator line_start = buffer.iterator_at(coord);
+        DisplayBuffer::iterator atom_it = display_buffer.atom_containing(line_start);
+        if (atom_it != display_buffer.end())
+        {
+            if (atom_it->begin() != line_start)
+            {
+                if (not atom_it->splitable())
+                    continue;
+
+                atom_it = display_buffer.split(atom_it, line_start) + 1;
+            }
+            atom_it = display_buffer.insert(
+                atom_it,
+                DisplayAtom(atom_it->coord(),
+                            atom_it->begin(), atom_it->begin(),
+                            Color::Black, Color::White));
+
+            char buffer[6];
+            snprintf(buffer, 6, "%3d ", coord.line);
+            display_buffer.replace_atom_content(atom_it, buffer);
+        }
+    }
+}
+
 }

src/filters.hh

@@ -13,6 +13,7 @@ void colorize_regex(DisplayBuffer& display_buffer,
 void colorize_cplusplus(DisplayBuffer& display_buffer);
 void colorize_cplusplus(DisplayBuffer& display_buffer);
 void expand_tabulations(DisplayBuffer& display_buffer);
+void show_line_numbers(DisplayBuffer& display_buffer);
 
 }
 

src/window.cc

@@ -114,6 +114,7 @@ Window::Window(Buffer& buffer)
     m_filters.push_back(colorize_cplusplus);
     m_filters.push_back(expand_tabulations);
     m_filters.push_back(HighlightSelections(*this));
+    m_filters.push_back(show_line_numbers);
 }
 
 void Window::check_invariant() const