through the OpenGEX and COLLADA formats. This enables the use of content from a large number of digital content creation programs such as Autodesk Maya or 3D Studio Max. Script editor The World Editor tool includes a graphical script editor designed to be accessible to artists and level designers as well as programmers. The script editor allows the user to place various "methods" into a directed graph connected by "fibers" representing action dependencies and the order of execution. Scripts support loops through the creation of cycles in the graph structure, and conditional execution is supported by marking fibers to be followed or not followed based on the result value output by the methods at which they start. The engine ships with several standard script methods that perform simple actions such as enabling or disabling a scene node (for example, to turn a light on or off) and more complex actions such as evaluating an arbitrary mathematical expression. New script methods can be defined by the game code, and they appear in the script editor as custom actions that can be used by a level designer. Panel editor The World Editor tool includes a sub-editor called the "panel editor" providing for the creation of 2D interface panels that can be placed inside a 3D world. The panel editor lets the user place various types of widgets such as text and images in a panel effect node that is rendered as part of the scene. Panels can also include a special camera widget that displays the scene that is visible to a camera placed anywhere else in the same world. Interface panels are both dynamic and interactive. The engine provides an extensible set of "mutators" that can be applied to individual panel items to induce various forms of animation such as scrolling, rotation, or color change. A character in a game can interact with a panel by approaching it and clicking the mouse inside interactive items. Script can be attached to such items, causing a sequence of actions to occur when the player activates them. Licensing The C4 Engine is licensed for $100 per person, and this includes all future updates at no additional cost. Academics The C4 Engine has been licensed by many universities in connection with games-oriented software engineering curricula or for special research projects. These universities include MIT, Georgia Tech, Worcester Polytechnic Institute (WPI), McMaster University, and the University