Figure 31.8 A Boolean-filter node type.
31fig08.wrl	Click on the image to view the VRML scene.

#VRML V2.0 utf8
# The VRML 2.0 Sourcebook
# Copyright (c) 1997
# Andrea L. Ames, David R. Nadeau, and John L. Moreland
PROTO BooleanFilter [
    eventIn  SFBool set_boolean
    eventOut SFBool true_changed
    eventOut SFBool false_changed
] {
    Script {
        eventIn  SFBool set_boolean   IS set_boolean
        eventOut SFBool true_changed  IS true_changed
        eventOut SFBool false_changed IS false_changed
        url "javascript:
            function set_boolean( bool, eventTime ) {
                if ( bool == true ) { true_changed  = true; }
                else                { false_changed = true; }
            }"
    }
}