Phasing is a technique commonly used in MMORPGs. This refers to the technique of having a certain area look differently to different characters.
How it Works
Data on the location of game objects, players, and NPCs is not stored in the World of Warcraft client and must be sent from the server. Phasing in a sense, decides not to send certain data based on criteria.
As a example, you may have a quest to get the head of a named NPC. After turning in the quest the server records not to send data on that NPC to you. The next time you go there despite how the NPC is still there, you will not be able to see it.
By using combinations of phasing entire areas can change from grasslands to a city by use of game object phasing and NPC phasing.
Appearance
NPC phasing is recognized by a NPC which should be at a location, but is completely gone when viewed by someone else.
Player phasing is recognized by not being able to see a player. Early uses of this was stealth and invisibility effects which caused the server to only show hidden players to certain people.
Game object phasing is the easiest to recognize and usually requires multiple phasing techniques. Game objects can be anything from a chair or chest, to a building. In most cases, players that can interact with phased buildings must also be phased, otherwise it would appear that players were walking in the air.
Current Usage in World of Warcraft
Currently phasing is used in stealth and invisibility mechanics. Events such as the opening of Ahn'Qiraj and the taking over of the Isle of Quel'danas was simply different realm databases adding game objects and NPCs for all players.
In Wrath of the Lich King
In the upcoming expansion, Blizzard is going to make full use of this system. The most well-known examples are Acherus: The Ebon Hold which looks differently to the character depending on his progress through the DK questline; and the Angrathar the Wrath Gate line of quests, ending with Quest:The Battle For The Undercity (Alliance) for Alliance and Quest:The Battle For The Undercity (Horde) for Horde characters.
To characters having completed the questline, Alexstrasza will be located in front of the Wrath Gate and Varimathras, who was killed along with Grand Apothecary Putress will no longer be in Undercity. Also, Putress will most likely have disappeared from the Apothecary Camp in Shattrath. For players on certain steps of the quest, the Undercity will also be inhabited by demons. Another example is the existence of Alliance NPCs in front of the Undercity which are not visible to players in a different phase of the quest.
Phasing is also used in:
- Nessingwary base camp - Flightpath
- The Argent Vanguard - The most quests completed for the faction, the stronger the offensive against the scourge.
- The Shadow Vault - You help take over the area from the scourge, turning it into a Knights of the Ebon Blade questhub.
- One of the horde cities changes their leader, and all players with different leaders will be phased out.
- Several kill quests use phasing to avoid griefing and make it more realistic.
- Sons of Hodir City.