if overlap(sx, sx+Display_settings.column_width, Display_settings.x, Display_settings.x + App.screen.width) then

    if overlap(sx-Margin_left, sx+Display_settings.column_width+Margin_right, Display_settings.x, Display_settings.x + App.screen.width) then

              pane.screen_top1, y_offset = schema1_of_y(pane, Display_settings.y - Margin_top)
--?               print(('%d,%d: => %d,%d'):format(column_index, pane_index, pane.screen_top1.line, pane.screen_top1.pos))

              pane.screen_top1, y_offset = schema1_of_y(pane, Display_settings.y - sy)
--?               print(('%d,%d: => %d,%d with offset %d'):format(column_index, pane_index, pane.screen_top1.line, pane.screen_top1.pos, y_offset))

--?           print(('%d,%d; %d,%d: adjusting pane top %d; screen_top is at %d,%d (max %d)'):format(column_index,pane_index, sx,sy, pane.top, pane.screen_top1.line, pane.screen_top1.pos, #pane.lines))

--?           print(('%d,%d; %d,%d: adjusting pane top %d; screen_top is at %d,%d (max %d); y_offset is %d'):format(column_index,pane_index, sx,sy, pane.top, pane.screen_top1.line, pane.screen_top1.pos, #pane.lines, y_offset))

--?   print('draw', Display_settings.x, Display_settings.y)

  assert(Cursor_pane.col)
  assert(Cursor_pane.row)
--?   print('==== draw', Display_settings.x, Display_settings.y)

--?         print('', pane_index, pane.id, 'of height', Cache[pane.id].height)

--?           print('', 'drawing', pane.top)

          pane.cursor_y = false

          pane.cursor_y = nil

    local old_top = {line=pane.screen_top1.line, pos=pane.screen_top1.pos}

    Display_settings.y = up_edge_sy(Cursor_pane.col, Cursor_pane.row) + y_of_schema1(pane, pane.screen_top1)
    Display_settings.y = Display_settings.y - Margin_top  -- don't hide under column headers
--?     print(('display settings.y is now %d'):format(Display_settings.y))
    Surface.cursor_on_screen_check = true  -- cursor was on screen before keystroke, so it should remain on screen after

--?     print('screen top after:', pane.screen_top1.line, pane.screen_top1.pos)
    if not eq(old_top, pane.screen_top1) then  -- and not eq(pane.screen_top1, {line=1, pos=1}) then
      Display_settings.y = up_edge_sy(Cursor_pane.col, Cursor_pane.row) + y_of_schema1(pane, pane.screen_top1)
      Display_settings.y = Display_settings.y - Margin_top  -- don't hide under column headers
--?       print(('display settings.y is now %d'):format(Display_settings.y))
      Surface.cursor_on_screen_check = true  -- cursor was on screen before keystroke, so it should remain on screen after
    end

  assert(y >= 0)

--?     print('--', y_offset)

--?         print(y_offset, pane.line_height, nlines)
        assert(nlines >= 0 and nlines < #pane.line_cache[i].screen_line_starting_pos)

* move mouse off any panes, press down and drag upwards. Panes don't flicker out before they go out of view.

* select a pane that isn't topmost on column, hit ctrl+x, type a key. Surface does not pan.
* select a pane that isn't topmost on column, hit ctrl+x, hit page down. Cursor remains visible.

[todo]

* select text. select some other text. first selection is no longer highlighted.
* select a pane, hit ctrl+x, hit pagedown, hit up arrow a few times. cursor continues to remain on screen.
* hit pagedown twice. Columns continue to scroll (even when cursor pane is off screen).