up-editor/mouse.lua

function update_mouse()
  mouse_x, mouse_y = love.mouse.getX(), love.mouse.getY() --mouse position
  mouse_x = math.floor(mouse_x / scale)
  mouse_y = math.floor(mouse_y / scale)
  clip_mouse_x = mouse_x - mouse_x % 16
  clip_mouse_y = mouse_y - mouse_y % 16
  --edition mode
  mouse_mode = 0
  if love.mouse.isDown(1) then
    mouse_mode = 1
  elseif love.mouse.isDown(2) then
    mouse_mode = -1
  end
  if mouse_mode == 0 then buffer_x, buffer_y = 0, 0 end
  --add to layer if
  if mouse_mode == 1 and (clip_mouse_x ~= buffer_x or clip_mouse_y ~= buffer_y) then
    set_tile(tiles_char[selected_tile])
    buffer_x = clip_mouse_x
    buffer_y = clip_mouse_y
  end
  --delete of layer if
  if mouse_mode == -1 and (clip_mouse_x ~= buffer_x or clip_mouse_y ~= buffer_y) then
    set_tile('.')
    buffer_x = clip_mouse_x
    buffer_y = clip_mouse_y
  end
end

function set_tile(char)
  pos = clip_mouse_x / 16 + 1 + clip_mouse_y / 16 * 26
  selected_screen = selected_screen:sub(1, pos - 1)..char..
  selected_screen:sub(pos + 1, -1)
end