structure InputMessage =
struct
  datatype t =
    MOUSE_MOVE of {x: Real32.real, y: Real32.real}
  | MOUSE_LEFT_CLICK
  | MOUSE_LEFT_RELEASE
  | RESIZE_WINDOW of {width: int, height: int}
  | UNDO_ACTION
  | REDO_ACTION
  | KEY_R
  | KEY_G
  | KEY_B
  | KEY_T
  | KEY_A
  | KEY_W
  | KEY_H
  | KEY_M
  | KEY_C
  | KEY_L
  | KEY_F
  | KEY_BACKSPACE
  | KEY_CTRL_S
  | KEY_CTRL_L
  | KEY_CTRL_E
  | KEY_CTRL_C
  | KEY_ESC
  | NUM of int
  | ARROW_UP
  | ARROW_LEFT
  | ARROW_RIGHT
  | ARROW_DOWN
  | KEY_ENTER
  | KEY_SPACE
  | USE_LAYERS of {tree: LayerTree.t, canvasWidth: int, canvasHeight: int}
  | SQUARES_LOAD_ERROR
end