Original Link (now dead) - http://acdm.turbinegames.com/featuredarticles/?action=view&article_id=142
Quest Implementation: Rolling Ball of Death
By Alicia Brown
Many players tend to think of NPCs as those cuddly vendors we sell our junk to after a long day's hunt. But in the Gaerlan quest, NPCs were set up to try to kill them. Not that the players ever see them! As part of our series about the creation of the Gaerlan quest we present an "insider's view" into the creation of the Rolling Ball of Death (RBoD) used in the Proving Grounds within the Gaerlan quest.
The first complication came when the balls were not sizing correctly, so that players would have been able to run around (and easily avoid) them. At this point, the art and tech teams jumped in to correct this problem. As you can now see below, the RBoD came into existence because an invisible NPC actually casts a spell (and no, in case you were wondering, players cannot attack them because they have no physics, i.e., physical aspects). So the RBoDs are actually spells. However, when the RBoDs were sized to fill the hallway, its physics caused problems by getting stuck in the hallway.
Here an explanation is in order. When any physical game object is created, two models are created; one is what the players see and the other is something more simple (like a sphere, cylinder or cube) that, while invisible to the players, defines the object's physics. This latter is what players actually collide with and cannot walk through. So, to continue, when they tried to size the physics down, the RBoD would get stuck on players - but would not "hit" them.
An ever increasing amount of time - about an hour a day for close to a week, then four hours on the last day - was spent trying to understand and find a fix for the problem, until finally it was realized that the physics object was not sizing with the visible model. Just 20 minutes later and they fixed and integrated it: All they had to do was ascertain what the scale was for the invisible physical object. That allowed them to make the physical model and the visible model exactly the same size - which meant the RBoD now rolled down the hallway killing everyone it touched!
Speed recalls: "Huxt and I beat our heads against the computer trying to get them to work correctly. We'd just about given up hope when we finally figured out what was happening with the spells. It felt really good to get those evil spells working correctly! *Evil Laugh*"
Once that hurdle was cleared, Speed decided he wanted to spice things up and added several variants of the short corridor ball rolling. "I was unhappy to hear about those spells killing players at the portal in the spot for the 'hallway of death'," he added. "That Proving Ground was supposed to kill the unwary player, but not right on entry. Still, it's one of the coolest interactive traps in the game so far and I was proud that I helped make it happen.
