BufferView updates cursor screen row to follow moved cursor

src/core/BufferView.cc

@@ -34,12 +34,14 @@ BufferView::Iterator BufferView::vert_iter()
     return Iterator(*this);
 }
 
-/**************************************************************************
- * Internal functions
- *************************************************************************/
-
 void BufferView::update()
 {
+    /* Update the cursor screen row in case the cursor position changed. */
+    m_cursor_screen_row = determine_new_cursor_screen_row();
+
+    /* Limit the cursor screen row taking into account view dimensions,
+     * available buffer contents above and below the current line, and scroll
+     * offset. */
     std::list<std::pair<int, std::shared_ptr<Buffer::Iterator>>> backward_lines;
     auto start_of_line = std::make_shared<Buffer::Iterator>(*m_iterator);
     start_of_line->go_start_of_line();
@@ -93,6 +95,34 @@ void BufferView::update()
     }
 }
 
+/**************************************************************************
+ * Internal functions
+ *************************************************************************/
+
+int BufferView::determine_new_cursor_screen_row()
+{
+    if (m_lines.size() > 0)
+    {
+        if (m_iterator->line() < m_lines.begin()->line->line())
+        {
+            return 0;
+        }
+        if (m_iterator->line() > m_lines.rbegin()->line->line())
+        {
+            return m_height;
+        }
+        for (const LineDescriptor & screen_line : m_lines)
+        {
+            if (screen_line.line->line() == m_iterator->line())
+            {
+                calculate_rows_in_cursor_line(screen_line.line);
+                return screen_line.row_offset + m_cursor_row_offset;
+            }
+        }
+    }
+    return 0;
+}
+
 int BufferView::calculate_rows_in_line(std::shared_ptr<Buffer::Iterator> start_of_line)
 {
     int saved_row_offset = 0;

src/core/BufferView.h

@@ -89,6 +89,7 @@ protected:
     {
         return std::min(m_scroll_offset, (m_height - 1) / 2);
     }
+    int determine_new_cursor_screen_row();
     int calculate_rows_in_line(std::shared_ptr<Buffer::Iterator> start_of_line);
     int calculate_rows_in_cursor_line(std::shared_ptr<Buffer::Iterator> start_of_line);
     int screen_rows_below_line(std::shared_ptr<Buffer::Iterator> line);

test/src/test_BufferView.cc

@@ -137,3 +137,55 @@ TEST(BufferViewTest, fills_view_with_last_lines_of_buffer_when_cursor_warps_to_l
     EXPECT_EQ(0, bv.cursor_screen_column());
     EXPECT_EQ(0, bv.cursor_virtual_column());
 }
+
+TEST(BufferViewTest, adjusts_cursor_row_as_cursor_moves)
+{
+    auto b = buffer1();
+    auto iterator = b->add_iterator();
+    BufferView bv(b, iterator, Cwd);
+    bv.resize(5, 5);
+    bv.update();
+    EXPECT_EQ(0, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 1
+    bv.update();
+    EXPECT_EQ(1, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 2
+    bv.update();
+    EXPECT_EQ(2, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 3
+    bv.update();
+    EXPECT_EQ(3, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 4
+    bv.update();
+    EXPECT_EQ(4, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 5
+    bv.update();
+    EXPECT_EQ(4, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 6
+    bv.update();
+    EXPECT_EQ(4, bv.cursor_screen_row());
+    iterator->go_next_line(); // to 7
+    bv.update();
+    EXPECT_EQ(4, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 6
+    bv.update();
+    EXPECT_EQ(2, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 5
+    bv.update();
+    EXPECT_EQ(1, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 4
+    bv.update();
+    EXPECT_EQ(0, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 3
+    bv.update();
+    EXPECT_EQ(0, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 2
+    bv.update();
+    EXPECT_EQ(0, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 1
+    bv.update();
+    EXPECT_EQ(0, bv.cursor_screen_row());
+    iterator->go_previous_line(); // to 0
+    bv.update();
+    EXPECT_EQ(0, bv.cursor_screen_row());
+}