if (!mon->visible())

        if (!you.can_see(mon))

            - ((!act || act->visible()) ? 0 : 10)

            - ((!act || act->visible_to(&you)) ? 0 : 10)

    if (monster->visible())

    if (monster->observable())

actor.o \

    attacker_visible   = attacker->visible() || crawl_state.arena;

    attacker_visible   = attacker->observable();

    defender_visible   = (defender && (defender->visible()
                                       || crawl_state.arena));

    defender_visible   = defender && defender->observable();

        if (!mon->visible())

        if (!you.can_see(mon))

    // Would looker be able to see the actor when in LOS?

    // Is the given cell within LOS of the actor?

    // Can the actor actually see the target?

    // Visibility as required by messaging. In usual play:
    //   Does the player know what's happening to the actor?
    virtual bool observable();

#include "AppHdr.h"
#include "actor.h"
#include "player.h"
#include "state.h"
bool actor::observable()
{
    return (crawl_state.arena || this == &you || you.can_see(this));
}