window: support scrolling

src/main.cc

@@ -11,12 +11,14 @@ using namespace Kakoune;
 
 void draw_window(Window& window)
 {
-    window.update_display_buffer();
-
     int max_x,max_y;
     getmaxyx(stdscr, max_y, max_x);
     max_y -= 1;
 
+    window.set_dimensions(LineAndColumn(max_y, max_x));
+    window.update_display_buffer();
+
+
     LineAndColumn position;
     for (const DisplayAtom& atom : window.display_buffer())
     {

src/window.cc

@@ -170,4 +170,29 @@ void Window::set_dimensions(const LineAndColumn& dimensions)
     m_dimensions = dimensions;
 }
 
+void Window::scroll_to_keep_cursor_visible_ifn()
+{
+    if (m_cursor.line < 0)
+    {
+        m_position.line = std::max(m_position.line + m_cursor.line, 0);
+        m_cursor.line = 0;
+    }
+    else if (m_cursor.line >= m_dimensions.line)
+    {
+        m_position.line += m_cursor.line - (m_dimensions.line - 1);
+        m_cursor.line = m_dimensions.line - 1;
+    }
+
+    if (m_cursor.column < 0)
+    {
+        m_position.column = std::max(m_position.column + m_cursor.column, 0);
+        m_cursor.column = 0;
+    }
+    else if (m_cursor.column >= m_dimensions.column)
+    {
+        m_position.column += m_cursor.column - (m_dimensions.column - 1);
+        m_cursor.column = m_dimensions.column - 1;
+    }
+}
+
 }

src/window.hh

@@ -57,6 +57,7 @@ public:
     void update_display_buffer();
 
 private:
+    void scroll_to_keep_cursor_visible_ifn();
 
     std::shared_ptr<Buffer> m_buffer;
     LineAndColumn           m_position;