Support for breeding

One party initiates the breeding; the other party exerts most of the
energy if its breeding key matches. It is that party's responsibility to
set up the newborn agent's connection (but the father can pass it an
arbitrary message). Newborn is spawned immediately but can be
renegotiated on first connect.

agent.cc

@@ -91,6 +91,53 @@ agent::attack_dir(int dir_x, int dir_y)
 	return attack_roll >= defense_roll;
 }
 
+bool
+agent::breed_dir(int dir_x, int dir_y, std::string info)
+{
+	if (dead || !tile)
+		return false;
+
+	class tile *t2 = &tile->tile_in_dir(dir_x, dir_y);
+	class agent *a = t2->agent;
+	if (!a || a->dead || !a->conn)
+		return false;
+
+	/* Self-breeding may not be a bad thing, but there is just
+	 * a technical problem with in/out buf locking. */
+	assert(a != this);
+
+	if (abs(a->attr.breeding_key - attr.breeding_key) > world::breeding_kappa)
+		return false;
+
+	chenergy(world::breed_out_cost);
+	a->chenergy(world::breed_in_cost);
+	if (a->dead)
+		return false;
+
+	/* Grab a tile. */
+	int spawn_dirs[][2] = {
+		{0,-1}, {1,-1}, {1,0}, {1,1}, {0,1}, {-1,1}, {-1,0}, {-1,-1},
+	};
+	int spawn_dir_n = sizeof(spawn_dirs) / sizeof(spawn_dirs[0]);
+	class tile *tb = NULL;
+	for (int i = 0; i < spawn_dir_n; i++) {
+		class tile *t = &tile->tile_in_dir(spawn_dirs[i][0], spawn_dirs[i][1]);
+		if (!t->agent) {
+			tb = t;
+			break;
+		}
+	}
+	if (!tb)
+		return false; // still-born
+
+	/* New agent, yay. */
+	class agent *ab = new class agent(agent_id++, NULL, map);
+	agents.push_back(ab);
+	ab->spawn_at(*tb);
+	a->conn->bred(ab->id, info);
+	return true;
+}
+
 bool
 agent::secrete(int id, double intensity)
 {