Interpolation Techniques

This blog will spotlight the various linear, spline and slerp interpolations found in World of Warcraft.  Being such a large game there are multitudes of interpolation uses found in the game.  I will go over several of the more prominent and noticeable applications.

First, being an MMO there are thousands of enemies scattered throughout Azeroth and beyond.  While questing out in the world your character is often beset upon by these monsters when you enter within a certain range of them.  Once in combat, the enemy will proceed to move toward your character using linear interpolation pathfinding.  They will find the most direct route and head toward you.

 







Lerp is also used for the thousands of character and object animations in WoW.  A very good example of the lerp (with skeletal-based skinning) is the dancing animations for the various races of Azeroth.  The model smoothly move from pose to pose in a rather intricate show of model morphing.

Another key feature (and important mechanic-wise) is the camera in WoW.  It defaults as 3rd person but can be zoomed in fully to present you with a 1st person view.  In almost every situation you're going to want it fully zoomed out though.  It follows the same principle as a car: you want to be aware of your surroundings at all times.  The camera is instrumental  because it allows you to view the necessary areas around your character to keep you informed of what is happening.

(servers are down so screenshots are not my own)

The camera in WoW must use Quaternion Slerp for this as it is an essential tool for the player.  In real time you can zoom in and out, and rotate the camera around your character to view anything you want.  The rotations are smooth and there are no problems with Gimbal Lock (does not use Euler Angles!!)  With an intuitive and flexible camera system, the world of Azeroth would be a much more difficult place to explore.

Spline interpolations are also found in many different parts of WoW.  Because all projectiles in WoW will auto-hit their target regardless of its location, projectiles will often curve midair to reach their goal.  Spline interpolation dictates that the projectile will follow a smooth curve from its target to its destination (ouch!).  If the enemy moves, the spline is automatically re-calculated to compensate for all changing factors.  Watch for the blue projectiles in the following video.

This is just a few examples, but in a game of WoW's scale there are many different uses for interpolation and the World of Warcraft would not be the same without it.