Collision Node

If you're not familiar to grouping nodes in VRML see the section Creating Hierarchical Node Structures for general information on grouping.

By default, all objects in the scene are collidable, i.e. you shouldn't be allowed to walk through walls and all that stuff. This is the theory, in practice some browsers still allow you to play ghosts.

So why do you need a collision node if collision is by default detected? Here are a few reasons to use this node:

turn off collision: This may seem a dumb thing to do but it will provide better performance.

provide alternative representations for collision: collision detection is hard work for the browser, complex worlds have lots of faces. This node allows you to provide an alternative graphical representation for collision. If this alternative representation is simpler than the real thing, then collision detection is easier to do. The alternative representation is not drawn, it is only used for collision detection purposes.

do something when collision occurs: The Collision node outputs an event collideTime, which outputs the time of collision. For example, this event can be routed to an AudioClip node to play a sound when the user collides with an object. The example at the bottom of this page shows the code to implement this.

The following fields are present:

children which contains all the nodes included in the group.

collide, a boolean field which specifies if the children nodes are eligible for collision detection.

proxy specifies an alternative geometric representation for collision detection. This field takes as value any node, except those which can only appear inside another node as AudioClip, MovieTexture, geometry nodes, etc...

bboxCenter specifies the center of a box that encloses the nodes in the group. The value for this field is a 3D point.

bboxSize specifies where the size of a box that encloses the nodes in the group. By default this field has a value of -1 -1 -1, which implies that no box is defined. The values for this field must be greater than or equal to zero. If the children nodes do not fit inside the box defined the results are undefined.

Detecting collision in a complex object

The latter two fields are optional. They can be used by the browser for optimization purposes.

Syntax:

Collision {

children [ ]

collide TRUE

proxy NULL

bboxCenter 0 0 0

bboxSize -1 -1 -1

}

In the following example, when the user collides with the sphere a sound will be heard.

Example:

#VRML V2.0 utf8

DEF col Collision {

children [

Sound { source DEF ac AudioClip { loop FALSE pitch 1.0 url "ouch.wav" } }

Shape {

appearance Appearance { material Material {}}

geometry Sphere {}

}

]

}

ROUTE col.collideTime TO ac.set_startTime