Pane_background_color = {r=0.9, g=0.9, b=0, a=0.1}
Cursor_pane_background_color = {r=0.5, g=0.5, b=0, a=0.1}

  Cursor_pane = nil  -- surface column and row index, along with some cached data

  for _, column in ipairs(Surface) do

  for column_index, column in ipairs(Surface) do

      for _, pane in ipairs(column) do

      for pane_index, pane in ipairs(column) do

          App.color(Editor_background_color)

          if Cursor_pane and column_index == Cursor_pane.col and pane_index == Cursor_pane.row then
            App.color(Cursor_pane_background_color)
          else
            App.color(Pane_background_color)
          end

  -- duplicate some logic from App.draw

        end
        y = y + Margin_above + Cache[pane.id].height + Margin_below + Padding_vertical
      end
    end
    x = x + Margin_left + Display_settings.column_width + Margin_right + Padding_horizontal
  end
  return false
end
function to_pane(x,y)
  -- duplicate some logic from App.draw
  local sx,sy = to_surface(x,y)
  local x = Padding_horizontal
  for column_idx, column in ipairs(Surface) do
    if sx < x then
      return nil
    end
    if sx < x + Margin_left + Display_settings.column_width + Margin_right then
      local y = Margin_top
      for pane_idx, pane in ipairs(column) do
        if sy < y then
          return nil

        if sy < y + Margin_above + Cache[pane.id].height + Margin_below then
          return {col=column_idx, row=pane_idx}
        end

  if not in_pane(x,y) then

  if in_pane(x,y) then
    Cursor_pane = to_pane(sx,sy)
  else

Editor_background_color = {r=0.9, g=0.9, b=0, a=0.1}