Bumper
tested with 
+
+
This lesson deals about how to add and
remove children of nodes. Transform nodes have events
addChildren and removeChildren and you can add or remove
nodes (surprise!) with them.
We start with a setup of three boxes:
DEF leftBox Transform {
translation -5 0 0
children [
Shape {
appearance Appearance {
material Material { diffuseColor 1 0 0 }
}
geometry Box {}
}
]
}
DEF rightBox Transform {
translation 5 0 0
children [
Shape {
appearance Appearance {
material Material { diffuseColor 0 0 1 }
}
geometry Box {}
}
]
}
DEF onoff Transform {
translation 0 -5 0
children [
Shape {
appearance Appearance {
material Material { diffuseColor 0 1 0 }
}
geometry Box {}
}
]
}
We add a child called 'SphereChild' to the 'leftBox' Transform:
DEF leftBox Transform {
translation -5 0 0
children [
Shape {
appearance Appearance {
material Material { diffuseColor 1 0 0 }
}
geometry Box {}
}
DEF SphereChild Shape {
appearance Appearance {
material Material { diffuseColor 1 0 1 }
}
geometry Sphere { radius 1.2 }
}
]
}
The child has to be DEFed (DEF SphereChild) in order to use it later
in a script. The middle lower box gets a TouchSensor 'TS':
Transform {
translation 0 -5 0
children [
Shape {
appearance Appearance {
material Material { diffuseColor 1 0 1 }
}
geometry Box {}
}
DEF TS TouchSensor {}
]
}
So far everything is straightforward and easy. Take a quick look at the
bumper.wrl and the
bumper source. Next we have to
think about the script. To use the eventIns
addChildren/removeChildren we need corresponding
eventOuts which we will get from a Script node. The triggering
eventIn of the Script node is simply the isActive
eventOut of the TouchSensor. The Script's
eventOut is called 'child' and has to be of type MFNode
to be compatible with the eventIn/eventOuts
addChildren/removeChildren:
DEF S Script {
eventIn SFBool isActive
eventOut MFNode child
field MFNode testNode USE SphereChild
url "javascript:
function isActive(value) {
if(value) child = testNode;
}
"
}
Once the TouchSensor has fired its eventOut 'isActive' to the
Script node 'S' it will trigger the eventOut 'child' which
the MFNode 'testNode' has been assigned to. This field uses the node
'SphereChild' to pass a reference to the eventOut 'child'. The
ROUTEing now needs to go from the eventOut 'child' to the
eventIn removeChildren of the Transform 'leftBox' and
then to the eventIn addChildren of the Transform 'rightBox'.
ROUTE TS.isActive TO S.isActive
ROUTE S.child TO leftBox.removeChildren
ROUTE S.child TO rightBox.addChildren
When you click on the purple box you will see how the sphere will jump (bump)
to the right box. (
bumper.wrl
and the bumper source). You might
say that you could get the same effect with a translation but when e.g.
the 'parents' are moving you need to be able to add/remove children. You can
also experiment with commenting out the 'removeChildren' ROUTE or an
animated parent object as in bumper.wrl.
Copyright © 1996-98
Markus Roskothen. All rights reserved.