Send creatures another way when the bridge they were using is sold

source/entities/Creature.cpp

@@ -968,6 +968,14 @@ void Creature::doUpkeep()
         return;
     }
 
+    // The ground the creature is standing on, or the ground it is walking towards, may have
+    // stopped being walkable since it last decided anything. Selling or destroying a bridge
+    // is what does that: the tiles it covered go back to being lava or water, and nothing
+    // told the creatures using them. Both checks have to happen before the creature acts, so
+    // that it acts on where it can actually go.
+    checkStandsOnWalkableTile();
+    checkWalkPathIsStillValid();
+
     // Check to see if we have earned enough experience to level up.
     checkLevelUp();
 
@@ -2480,6 +2488,86 @@ bool Creature::setDestination(Tile* tile)
     return true;
 }
 
+void Creature::checkWalkPathIsStillValid()
+{
+    if(mWalkQueue.empty())
+        return;
+
+    bool isPathBlocked = false;
+    for(const Ogre::Vector2& step : mWalkQueue)
+    {
+        Tile* tile = getGameMap()->getTile(Helper::round(step.x), Helper::round(step.y));
+        if(canGoThroughTile(tile))
+            continue;
+
+        // A building that will not let the creature through, a closed door or a prison, is
+        // another matter: those are meant to stop it where it is, and it was already
+        // walking towards one knowing what it would find. Only the ground going away from
+        // under the path is unexpected.
+        if((tile != nullptr) && (tile->getCoveringBuilding() != nullptr))
+            continue;
+
+        isPathBlocked = true;
+        break;
+    }
+
+    if(!isPathBlocked)
+        return;
+
+    const Ogre::Vector2& lastStep = mWalkQueue.back();
+    Tile* destination = getGameMap()->getTile(Helper::round(lastStep.x), Helper::round(lastStep.y));
+
+    OD_LOG_INF("creature=" + getName() + " cannot walk its path anymore, destination="
+        + Tile::displayAsString(destination));
+
+    // Stop where we are rather than walk into what is now lava or water. If there is no
+    // other way to the destination, the action that started the walk gets to decide what
+    // to do instead, exactly as it would have done had the creature arrived.
+    clearDestinations(EntityAnimation::idle_anim, true, true);
+
+    if(!canGoThroughTile(destination))
+        return;
+
+    std::list<Tile*> result = getGameMap()->path(this, destination);
+    if(result.size() <= 1)
+        return;
+
+    std::vector<Ogre::Vector2> path;
+    tileToVector2(result, path, true, 0.0);
+    setWalkPath(EntityAnimation::walk_anim, EntityAnimation::idle_anim, true, true, path, true);
+}
+
+void Creature::checkStandsOnWalkableTile()
+{
+    Tile* myTile = getPositionTile();
+    if(canGoThroughTile(myTile))
+        return;
+
+    // Prisons, fenced rooms and locked doors give a null speed on purpose, to hold the
+    // creature where it is. What we are after here is the ground going away from under
+    // it, which leaves the tile covered by nothing at all.
+    if(myTile->getCoveringBuilding() != nullptr)
+        return;
+
+    // And a bridge is the only thing that can be taken away from under a creature, so
+    // water and lava are the only ground it can be left standing on. Anything else that
+    // gives a null speed is left alone rather than guessed at.
+    if((myTile->getTileVisual() != TileVisual::waterGround) &&
+       (myTile->getTileVisual() != TileVisual::lavaGround))
+    {
+        return;
+    }
+
+    // The creature cannot go through this tile, or canGoThroughTile above would have
+    // accepted it, so it cannot live in what it is now standing in. It does not get
+    // fished out or teleported ashore: it drowns, or burns.
+    OD_LOG_INF("creature=" + getName() + " lost the ground under its feet on tile="
+        + Tile::displayAsString(myTile) + " and dies");
+
+    clearDestinations(EntityAnimation::idle_anim, true, true);
+    takeDamage(nullptr, getHP(), 0.0, 0.0, 0.0, myTile, false);
+}
+
 bool Creature::wanderRandomly(const std::string& animationState)
 {
     // We pick randomly a visible tile far away (at the end of visible tiles)

source/entities/Creature.h

@@ -218,6 +218,17 @@ class Creature: public MovableGameEntity, public Subject
 
     bool setDestination(Tile* tile);
 
+    //! \brief Server side. Checks that the creature can still walk the path it is following and,
+    //! if it cannot, looks for another way to the same destination. Tiles the creature could walk
+    //! on when the path was computed can stop being walkable while it is on its way, which is what
+    //! happens to a bridge over lava or water that is sold or destroyed.
+    void checkWalkPathIsStillValid();
+
+    //! \brief Server side. Checks that the creature is standing somewhere it can stand and, if
+    //! the ground has turned into water or lava it cannot live in, kills it. A creature on a
+    //! tile it cannot walk on has a null move speed, so it could never leave by itself anyway.
+    void checkStandsOnWalkableTile();
+
     //! \brief Picks a destination far away in the visible tiles and goes there
     //! Returns true if a valid Tile was found. The creature will go there
     //! Returns false if no reachable Tile was found

source/network/ODClient.cpp

@@ -608,8 +608,13 @@ bool ODClient::processMessage(ServerNotificationType cmd, ODPacket& packetReceiv
 
             OD_ASSERT_TRUE(packetReceived >> objName >> dest);
             MovableGameEntity *obj = gameMap->getAnimatedObject(objName);
+            if (obj == nullptr)
+            {
+                OD_LOG_ERR("Server told us to teleport unknown entity name=" + objName);
+                break;
+            }
             obj->setPosition(dest);
-            
+
             break;
         }
         case ServerNotificationType::entitySlapped: