Unlock cursor from first screen row

src/gui/Window.cc

@@ -134,6 +134,7 @@ bool Window::create(std::shared_ptr<Buffer> buffer)
     m_cursor = m_buffer->piece_table->add_cursor();
     m_start_piece = m_buffer->piece_table->start_piece->next;
     m_cursor_row = 0;
+    m_scroll_offset = 5;
 
     resize();
 
@@ -234,42 +235,73 @@ void Window::handle_key(uint32_t scancode, uint32_t mod)
         m_exit_requested = true;
         break;
     case SDL_SCANCODE_H:
-        cursor_left();
+        cursor_move(CURSOR_LEFT);
         break;
     case SDL_SCANCODE_J:
-        cursor_down();
+        cursor_move(CURSOR_DOWN);
         break;
     case SDL_SCANCODE_K:
-        cursor_up();
+        cursor_move(CURSOR_UP);
         break;
     case SDL_SCANCODE_L:
-        cursor_right();
+        cursor_move(CURSOR_RIGHT);
         break;
     }
 }
 
-void Window::cursor_left()
+void Window::cursor_move(int which)
 {
-    if (m_cursor->go_left(1))
+    bool success = false;
+    int current_row_offset = m_cursor->column / m_columns;
+    int row_offset = 0;
+
+    switch (which)
+    {
+    case CURSOR_LEFT:
+        success = m_cursor->go_left(1);
+        break;
+    case CURSOR_RIGHT:
+        success = m_cursor->go_right(1);
+        break;
+    case CURSOR_UP:
+        success = m_cursor->go_up(1, m_cursor->column);
+        break;
+    case CURSOR_DOWN:
+        success = m_cursor->go_down(1, m_cursor->column);
+        break;
+    }
+    if (success)
+    {
+        switch (which)
+        {
+        case CURSOR_LEFT:
+        case CURSOR_RIGHT:
+            row_offset = m_cursor->column / m_columns - current_row_offset;
+            break;
+        case CURSOR_UP:
+            {
+                PieceTable::Cursor c = *m_cursor;
+                c.go_end_of_line();
+                row_offset = m_cursor->column / m_columns - c.column / m_columns - 1 - current_row_offset;
+            }
+            break;
+        case CURSOR_DOWN:
+            {
+                PieceTable::Cursor c = *m_cursor;
+                c.go_up(1, 0u);
+                c.go_end_of_line();
+                row_offset = c.column / m_columns - current_row_offset + 1 + m_cursor->column / m_columns;
+            }
+            break;
+        }
+        update_cursor_row(m_cursor_row + row_offset);
         redraw();
     }
-
-void Window::cursor_right()
-{
-    if (m_cursor->go_right(1))
-        redraw();
 }
 
-void Window::cursor_up()
+void Window::update_cursor_row(int cursor_row)
 {
-    if (m_cursor->go_up(1, m_cursor->column))
+    m_cursor_row = std::max(m_scroll_offset, std::min(m_rows - m_scroll_offset - 1, cursor_row));
-        redraw();
-}
-
-void Window::cursor_down()
-{
-    if (m_cursor->go_down(1, m_cursor->column))
-        redraw();
 }
 
 std::pair<int, PieceTable::Cursor> Window::calculate_start_position()

src/gui/Window.h

@@ -16,18 +16,24 @@ public:
     void run_event_loop();
 
 protected:
+    enum
+    {
+        CURSOR_LEFT,
+        CURSOR_RIGHT,
+        CURSOR_UP,
+        CURSOR_DOWN,
+    };
+
     void resize();
     void redraw();
     void draw_cursor(int screen_column, int screen_row);
     void handle_event(SDL_Event & event);
     void handle_key(uint32_t scancode, uint32_t mod);
-    void cursor_left();
+    void cursor_move(int which);
-    void cursor_right();
-    void cursor_up();
-    void cursor_down();
     std::pair<int, PieceTable::Cursor> calculate_start_position();
     void draw_text();
     void draw_character(int screen_column, int screen_row, uint32_t character);
+    void update_cursor_row(int cursor_row);
 
     SDL_Window * m_window;
     bool m_exit_requested;
@@ -43,6 +49,7 @@ protected:
     int m_columns;
     int m_rows;
     int m_cursor_row;
+    int m_scroll_offset;
 
     std::shared_ptr<Buffer> m_buffer;