<table border="0" width="100%"> <tbody> <tr> <td align="left"> <p> Sensing viewer activity enables the scene to trigger animations. A VisibilitySensor node checks if a region is visible to the viewer, where the region is described by a center and a size. Time events are sent on entry and exit of visibility, and true/false is sent on entry and exit of visibility. A ProximitySensor node similarly checks if the viewer is within a region, also sending viewer position and orientation while within the sensed region. Collision is a grouping node that checks if the viewer has run into a shape defined by the node's children (or else simpler proxy geometry) with a collision time event sent upon contact. </p> <p> These X3D scenes are adapted directly from the <a href="http://www.wiley.com/legacy/compbooks/vrml2sbk/toc/ch27.htm" target="_Vrml2Sourcebook">original VRML 2.0 Sourcebook chapter examples</a>. Also available: <a href="http://www.sdsc.edu/~moreland/courses/Siggraph98/vrml97/slides/mt0366.htm" target="_Vrml2SourcebookCourse">Introduction to VRML97 SIGGRAPH98 course notes</a>. </p> </td> <td align="center" rowspan="2"> <a href="index.html"><img border="0" alt="Figure 27.1 Visibility Sensor Dungeon Sliding Doors" title="Figure 27.1 Visibility Sensor Dungeon Sliding Doors" hspace="10" src="Figure27_1VisibilitySensorDungeonSlidingDoors.png" width="156" height="89" align="middle"/></a> </td> </tr> </tbody> </table>