Support horizontal centering in view commands (using m)

Fixes #442

src/normal.cc

@@ -239,19 +239,23 @@ void view_commands(Context& context, NormalParams params)
         if (not cp or not context.has_window())
             return;
 
-        LineCount cursor_line = context.selections().main().cursor().line;
+        const ByteCoord cursor = context.selections().main().cursor();
         Window& window = context.window();
         switch (tolower(*cp))
         {
         case 'v':
         case 'c':
-            context.window().center_line(cursor_line);
+            context.window().center_line(cursor.line);
+            break;
+        case 'm':
+            context.window().center_column(
+                context.buffer()[cursor.line].char_count_to(cursor.column));
             break;
         case 't':
-            context.window().display_line_at(cursor_line, 0);
+            context.window().display_line_at(cursor.line, 0);
             break;
         case 'b':
-            context.window().display_line_at(cursor_line, window.dimensions().line-1);
+            context.window().display_line_at(cursor.line, window.dimensions().line-1);
             break;
         case 'h':
             context.window().scroll(-std::max<CharCount>(1, params.count));
@@ -267,7 +271,8 @@ void view_commands(Context& context, NormalParams params)
             break;
         }
     }, "view",
-    "v,c:  center cursor   \n"
+    "v,c:  center cursor (vertically)\n"
+    "m:    center cursor (horzontally)\n"
     "t:    cursor on top   \n"
     "b:    cursor on bottom\n"
     "h:    scroll left     \n"

src/window.cc

@@ -40,6 +40,11 @@ Window::~Window()
     options().unregister_watcher(*this);
 }
 
+void Window::scroll(LineCount offset)
+{
+    m_position.line = std::max(0_line, m_position.line + offset);
+}
+
 void Window::display_line_at(LineCount buffer_line, LineCount display_line)
 {
     if (display_line >= 0 or display_line < m_dimensions.line)
@@ -51,16 +56,22 @@ void Window::center_line(LineCount buffer_line)
     display_line_at(buffer_line, m_dimensions.line/2_line);
 }
 
-void Window::scroll(LineCount offset)
-{
-    m_position.line = std::max(0_line, m_position.line + offset);
-}
-
 void Window::scroll(CharCount offset)
 {
     m_position.column = std::max(0_char, m_position.column + offset);
 }
 
+void Window::display_column_at(CharCount buffer_column, CharCount display_column)
+{
+    if (display_column >= 0 or display_column < m_dimensions.column)
+        m_position.column = std::max(0_char, buffer_column - display_column);
+}
+
+void Window::center_column(CharCount buffer_column)
+{
+    display_column_at(buffer_column, m_dimensions.column/2_char);
+}
+
 size_t Window::compute_hash(const Context& context) const
 {
     size_t res = hash_values(m_position, context.ui().dimensions(), context.buffer().timestamp());

src/window.hh

@@ -23,10 +23,13 @@ public:
     const CharCoord& dimensions() const { return m_dimensions; }
     void set_dimensions(CharCoord dimensions);
 
+    void scroll(LineCount offset);
     void center_line(LineCount buffer_line);
     void display_line_at(LineCount buffer_line, LineCount display_line);
-    void scroll(LineCount offset);
+
     void scroll(CharCount offset);
+    void center_column(CharCount buffer_column);
+    void display_column_at(CharCount buffer_column, CharCount display_column);
 
     const DisplayBuffer& update_display_buffer(const Context& context);