How can link a URL to a location in my world?

Often, instead of linking an object to a URL using the Anchor node, you'll want to transport the user to a new URL when they enter a particular location, whether it's visible or not. For instance, you could create a house with a number of different rooms, where each room is a separate file. When the user walks into a doorway, you can transport them to another URL, rather than having to have them click on the door to go there.

So, how could we do this? Well, let's define what we want to get at the end of the day. We want something that we can use just like an Anchor, but that has a position in the world instead of being linked to an object. Let's create a PROTO that will allow us to do that:

PROTO ProximityAnchor [
  exposedField SFVec3f  center     0 0 0
  exposedField SFVec3f  size       0 0 0
  exposedField SFBool   enabled    TRUE
  exposedField MFString parameter  []
  exposedField MFString url        []
]

This gives us everything we need. It has the field required to position it in the world, and also enable and disable it (might be useful). It also has the fields we need to load a URL. It's kind of a combination of a ProximitySensor and an Anchor, and in fact, that's almost exactly what we're going to do.

The first thing we're going to pu in the implementation is the ProximitySensor part. This means that from the outside of the PROTO, the ProximityAnchor looks like a normal ProximitySensor, and so can be used in any of the same places, which is good.

PROTO ProximityAnchor [
  exposedField SFVec3f  center     0 0 0
  exposedField SFVec3f  size       0 0 0
  exposedField SFBool   enabled    TRUE
  exposedField MFString parameter  []
  exposedField MFString url        []
]
{
  DEF SENSOR ProximitySensor {
    center  IS center
    size    IS size
    enabled IS enabled
  }
}

This gives us the means to detect when someone has entered the space. But what do we do then? Well, we need to load the URL with the appropriate parameters. Now, we can't use an Anchor for this, as we can't trigger an Anchor from outside. We're going to have to do it ourselves, using a Script node.

What does the Script node need to do? Well, in theory, it just need to be triggered when the ProximitySensor's enterTime event goes off, and load a URL. That'll be just fine. Let's try it.

PROTO ProximityAnchor [
  exposedField SFVec3f  center     0 0 0
  exposedField SFVec3f  size       0 0 0
  exposedField SFBool   enabled    TRUE
  exposedField MFString parameter  []
  exposedField MFString url        []
]
{
  DEF SENSOR ProximitySensor {
    center  IS center
    size    IS size
    enabled IS enabled
  }
  DEF ANCHOR Script {
    eventIn      SFTime   trigger
    exposedField MFString parameter  IS parameter
    exposedField MFString url        IS url
    url "javascript:
      function trigger(value,time) {
        Browser.loadURL(url,parameter);
      }
    "
  }
  ROUTE SENSOR.enterTime TO ANCHOR.trigger
}

And that's it! The sensor trigger the script, which loads a URL. However, can anyone spot the deliberate mistakes? Yes, that's right. Scripts can't have exposed fields. So, we have to change our PROTO and our Script. We want to keep the behaviour, as it's really useful sometimes, so we have to add eventIns and eventOuts. Also, we've got a duplicate field in our Script (i.e. two fields called 'url'), so we'll have to get rid of that as well. Let's do it.

PROTO ProximityAnchor [
  eventIn      MFString set_parameter
  eventIn      MFString set_url
  exposedField SFVec3f  center     0 0 0
  exposedField SFVec3f  size       0 0 0
  exposedField SFBool   enabled    TRUE
  field        MFString parameter  []
  field        MFString url        []
  eventOut     MFString parameter_changed
  eventOut     MFString url_changed
[
}
  DEF SENSOR ProximitySensor {
    center  IS center
    size    IS size
    enabled IS enabled
  }
  DEF ANCHOR Script {
    eventIn      SFTime   trigger
    eventIn      MFString set_parameter     IS set_parameter
    eventIn      MFString set_URL           IS set_url
    field        MFString parameter         IS parameter
    field        MFString URL               IS url
    eventOut     MFString parameter_changed IS parameter_changed
    eventOut     MFString URL_changed       IS url_changed
    url "javascript:
      function set_parameter(value,time) {
        parameter = value;
        parameter_changed = value;
      }
      function set_url(value,time) {
        URL = value;
        URL_changed = value;
      }
      function trigger(value,time) {
        Browser.loadURL(URL,parameter);
      }
    "
  }
  ROUTE SENSOR.enterTime TO ANCHOR.trigger
}

That should take care of it. Now, let's try it out. We'll create a simple world, with a cubicle in it, and then stick a ProximityAnchor inside the cubicle. We'll use a very simple URL, just one to open a javascript window to show it's working. Take a look at the result - when you walk into the cubicle, a javascript alert window should open up, telling you that the teleporter has been triggered. Also, take a look at the complete source code of the example, to see how we use our new node.