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## Display Update

Usually the interface's display is controlled by the player, but when `run_game` is executing, it will frequently change the state of an object in a way that needs to be reflected in the display immediately. Examples include units leaving or entering a cell, sides losing or winning, and so forth. The interface must define a set of callbacks that will be invoked by the kernel.

- `update_cell_display(side, x, y, rightnow)` [introduce area (radius or rect) update routines?]
- `update_side_display(side, side2, rightnow)`
- `update_unit_display(side, unit, rightnow)`
- `update_unit_acp_display(side, unit, rightnow)`
- `update_turn_display(side, rightnow)`
- `update_action_display(side, rightnow)`
- `update_action_result_display(side, unit, rslt, rightnow)`
- `update_fire_at_display(side, unit, unit2, m, rightnow)`
- `update_fire_at_display(side, unit, x, y, z, m, rightnow)`
- `update_event_display(side, hevt, rightnow)`
- `update_all_progress_displays(str, s)`
- `update_clock_display(side, rightnow)`
- `update_message_display(side, sender, str, rightnow)`
- `update_everything()`

Each of these routines has a flag indicating whether the change may be buffered or not. To ensure that buffered data is actually onscreen, the kernel may call `flush_display_buffers()`, which the interface must define.

- `flush_display_buffers()`

These may or may not be called on reasonable sides, so the interface should always check first that `side` actually exists and has an active display. [If side has a "remote" display, then interface has to forward?? No, because remote copy of game is synchronized and does own update_xxx calls more-or-less simultaneously]

Note that this is as much as the kernel interests itself in displays. Map, list, etc drawing and redrawing are under the direct control of the interface code.

Unix-hosted versions must provide `void close_displays()` for signal handlers to call.

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