The setviewereffect updates or creates a viewer effect (either LookAt, PointAt, beam or sphere).

llInstantMessage(CORRADE,
    wasKeyValueEncode(
        [
            // Start a beam effect to the
            // primitive in which this
            // script is placed.
            "command", "setviewereffect",
            "group", wasURLEscape(GROUP),
            "password", wasURLEscape(PASSWORD),
            "effect", "beam",
            "item", wasURLEscape(llGetKey()),
            "range", 5,
            "callback", wasURLEscape(URL)
        ]
    )
);

With the possible parameter tree:

Parameter	Possible Value	Sub-Parameter	Possible Value	Description
effect	look	item, range or agent by UUID (agent) or by firstname and lastname		Sets a LookAt on either an item in range or an avatar by agent UUID or by firstname and lastname.
		offset	A vector describing an offset from Corrade.
		type	A LookAt type.
	point	item, range or agent by UUID (agent) or by firstname and lastname		Sets a PointAt on either an item in range or an avatar by agent UUID or by firstname and lastname.
		offset	A vector describing an offset from Corrade.
		type	A PointAt type.
	beam	item, (optional range) or agent by UUID (agent) or by firstname and lastname		Sets a beam on either an item in range or an avatar by agent UUID or by firstname and lastname.
		color	An LSL color vector.
		alpha	A value in the interval describing the color alpha.
		duration	The duration (in seconds) for the effect.
		offset	A vector describing an offset from Corrade.
	sphere	color	An LSL color vector.	Creates a particle swirl effect.
		alpha	A value in the interval describing the color alpha.
		duration	The duration (in seconds) for the effect.
		offset	A vector describing an offset from Corrade.

The command takes an optional parameter id, an UUID corresponding to an effect:

and in case id is not specified, then Corrade will generate a random UUID and, in the case of the look viewer effect, it will create a new beacon.

• The command will return an UUID referenced by the data key via the callback which represents the UUID of the effect created or modified. This UUID can be used as a reference for both ulterior setviewereffect or deteleviewereffect calls. You most likely want to track the viewer effects for LookAt and PointAt in order to be able to change them.
• LookAt beacon(s) are tracked by the other surrounding viewers that sensed the beacon and thereby LookAt beacons cannot be removed.
  • All beacons will be cleared by other viewers when the agent teleports out of the simulator.
  • Conventionally, viewers will set the effect to the look at type Idle and then move on. When looking at something else, the beacon will be moved implicitly by reusing the same UUID.
• Compared to the workings of a regular viewer, Corrade can set multiple look at beacons, if you so desire, and it is up to the user to track and manage them using the returned UUIDs.
• Corrade can also trigger the point-at selection effect when selecting objects but without selecting the object simply by setting effect to point and type to Select.

The setviewereffect is a powerful command with which you can also make Corrade look at something or someone. Suppose that your name is Leslie Resident and that you would like your Corrade to look at you. In that case, you would issue the command as:

llInstantMessage(CORRADE, 
    wasKeyValueEncode(
        [
            "command", "setviewereffect",
            "group", llEscapeURL(GROUP),
            "password", llEscapeURL(PASSWORD),
            "effect", "look",
            "firstname", "Leslie",
            "lastname", "Resident",
            "offset", ZERO_VECTOR,
            "type", "Mouselook",
            "callback", llEscapeURL(URL)
        ]
    )
);

which will make Corrade look at Leslie Resident. You can also make Corrade look at an object the same way by using the item and optional range parameter.

If the command is successful, then Corrade will return the effect UUID in the data key to the callback URL. Suppose that Corrade returned the UUID af61fb35-8f84-4e28-a8d7-dd88c33ab99f, then this UUID can be used to make Corrade look at a different object by moving the beacon:

llInstantMessage(CORRADE, 
    wasKeyValueEncode(
        [
            "command", "setviewereffect",
            "group", llEscapeURL(GROUP),
            "password", llEscapeURL(PASSWORD),
            "effect", "look",
            "item", "46eda187-9382-4333-81df-4976ac5d8031",
            "range", 5,
            "offset", ZERO_VECTOR,
            "type", "Mouselook",
            "id", "af61fb35-8f84-4e28-a8d7-dd88c33ab99f",
            "callback", llEscapeURL(URL)
        ]
    )
);

Note the id that references the previous look beacon (af61fb35-8f84-4e28-a8d7-dd88c33ab99f). It is important to track the viewer effects because they can then be manipulated and set to different objects. The setviewereffect by default creates a new beacon in case an existing UUID is not supplied as the value of the id parameter. In other words, if you do not track your effects, Corrade will just create new beacons every time setviewereffect is called - this is especially true for the look viewer effect that cannot be deleted.