From afd584566ce46a05f3f379f64cbfabdc22e73723 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Wed, 9 Nov 2016 22:43:04 -0500
Subject: [PATCH] avoid empty screen rows if there is buffer content to fill
 them

---
 src/gui/Window.cc | 38 +++++++++++++++++++++++++++++++++++---
 src/gui/Window.h  |  8 +++++++-
 2 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/src/gui/Window.cc b/src/gui/Window.cc
index 3bb3d84..5cda39a 100644
--- a/src/gui/Window.cc
+++ b/src/gui/Window.cc
@@ -365,13 +365,19 @@ void Window::cursor_move(int which)
 #endif
 }
 
-void Window::update_cursor_row(int cursor_row)
+void Window::update_cursor_row()
 {
-    m_cursor_row = std::max(m_scroll_offset, std::min(m_rows - m_scroll_offset - 1, cursor_row));
+    int so = effective_scroll_offset();
+    int rows_above = screen_rows_above_cursor(std::max(so, m_cursor_row));
+    int rows_below = screen_rows_below_cursor(std::max(so, m_rows - m_cursor_row - 1));
+    int min_rows_to_leave_above = std::min(rows_above, so);
+    int min_rows_to_leave_below = std::min(rows_below, so);
+    m_cursor_row = std::max(min_rows_to_leave_above, std::min(m_rows - min_rows_to_leave_below - 1, m_cursor_row));
 }
 
 void Window::draw_buffer()
 {
+    update_cursor_row();
 }
 
 void Window::draw_buffer_character(int screen_column, int screen_row, uint32_t character)
@@ -403,7 +409,6 @@ void Window::resize()
     if (m_columns < 1)
         m_columns = 1;
     m_rows = (m_height - 2) / m_font.get_line_height();
-    update_cursor_row(m_cursor_row);
 }
 
 void Window::redraw()
@@ -533,3 +538,30 @@ uint32_t Window::get_shifted(uint32_t keysym)
 
     return keysym;
 }
+
+int Window::screen_rows_below_cursor(int stop_at)
+{
+    GapBuffer::Cursor cursor = *m_cursor;
+    size_t column = cursor.column();
+    cursor.go_end_of_line(false);
+    int rows = (cursor.column() / m_columns) - (column / m_columns);
+    while ((rows < stop_at) && cursor.go_down(0u))
+    {
+        cursor.go_end_of_line(false);
+        rows += (cursor.column() / m_columns) + 1;
+    }
+    return rows;
+}
+
+int Window::screen_rows_above_cursor(int stop_at)
+{
+    GapBuffer::Cursor cursor = *m_cursor;
+    int rows = cursor.column() / m_columns;
+    while ((rows < stop_at) && cursor.go_up(0u))
+    {
+        GapBuffer::Cursor cursor2 = cursor;
+        cursor2.go_end_of_line(false);
+        rows += (cursor2.column() / m_columns) + 1;
+    }
+    return rows;
+}
diff --git a/src/gui/Window.h b/src/gui/Window.h
index ecf5a0e..7e9341b 100644
--- a/src/gui/Window.h
+++ b/src/gui/Window.h
@@ -47,11 +47,17 @@ protected:
     void draw_buffer();
     void draw_buffer_character(int screen_column, int screen_row, uint32_t character);
     void draw_character(int x, int y, uint32_t character);
-    void update_cursor_row(int cursor_row);
+    void update_cursor_row();
     void draw_rect(int x, int y, int width, int height, float r, float g, float b, float a);
     void draw_status_bar();
     uint32_t get_keyval(SDL_Keycode keysym);
     uint32_t get_shifted(uint32_t keysym);
+    int screen_rows_below_cursor(int stop_at);
+    int screen_rows_above_cursor(int stop_at);
+    int effective_scroll_offset()
+    {
+        return std::min(m_scroll_offset, (m_rows - 1) / 2);
+    }
 
     SDL_Window * m_window;
     bool m_exit_requested;