Scripting Your World: The Official Guide to Second Life® Scripting

CHAPTER 5

134

BUILDING

SENSORS

DETECTION

WITH

COLLISIONS

USING

GREETERS TO

WELCOM E

VISITORS

SUMMARY

TABLE 5.1: QUERY PARAMETERS FOR llGetObjectDetails()

FLAG DESCRIPTION ALTERNATIVE FUNCTION

OBJECT_NAME

Gets the object's name as a string up to 63 characters long.

llKey2Name()

llDetectedName()

OBJECT_DESC

Gets the object's description (empty if avatar) as a string up to

127 characters long.

—

OBJECT_POS

Gets the object's position as a vector in region coordinates.

llDetectedPos()

OBJECT_ROT

Gets the object's rotation as a rotation.

llDetectedRot()

OBJECT_VELOCITY

Gets the object's velocity as a vector.

llDetectedVel()

OBJECT_OWNER

Gets an object's owner's UUID as a key. If group-owned or

avatar, a NULL_KEY is returned.

llDetectedOwner()

llGetOwnerKey()

OBJECT_GROUP

Gets the prims's group UUID as a key. If avatar, a NULL_KEY is

returned.

llDetectedGroup()

OBJECT_CREATOR

Gets the object's creator UUID as a key. If avatar, a NULL_KEY

is returned.

llGetCreator()

DET

E

CTION WITH COLLISIONS

In many situations a collision sensor is a cheaper way to detect things. You can place filters on the

collision events with llCollisionFilter(), which sets the name and/or key of the item to

detect and indicates whether to ignore or accept the collision. You can play sounds on collision via

llCollisionSound(), and use llPassCollisions() to control whether child prims tell the root

prim about collisions. The details are sketched in Table 5.2.

TABLE 5.2: COLLISION FUNCTIONS

FUNCTION BEHAVIOR

llCollisionFilter(string name,

key id, integer accept)

Filter collision events. Boolean accept; FALSE means reject collisions

from name, and TRUE means accept them.

llCollisionSound(string sound,

float volume)

Play sound on collisions instead of the default. The sound parameter

may be the name of a sound in inventory, a built-in sound, or the UUID

of a sound anywhere. If sound is an empty string ("") no sound is played.

volume ranges from 0.0 to 1.0.

llPassCollisions(integer pass)

Pass collisions to parents. If the parent is using a phantom volume detect,

then the child prim will not receive collision events and the child will also

become phantom.

Three events can be triggered—collision(), collision_start(), and collision_

end()—each taking the single parameter numDetected. Avatars and physical objects will trigger

collisions. Attachments and nonphysical objects won't.

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APPENDIC

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CHAPTER 5

collision_start(integer numDetected) {}

collision(integer numDetected) {}

collision_end(integer numDetected) {}

Events in the collision family are invoked in an object after an avatar or physical object collides with it.

collision_start() is triggered when the collision starts; collision() is triggered periodically

while the objects are colliding; collision_end() is triggered when the collision ends. Compare

to the touch() and land_collision() families of events in Chapters 2 and 7, respectively.

Additional documentation can be found on the SYW website.

numDetected — The number of objects or avatars that have collided.

EVENT

DEFINITION

Collisions are a nice, simple way to detect whether there's an avatar nearby, but the avatar will collide

with the object, and that may not be the effect you are after. However, because you can't simply make the

objects phantom so that avatars can walk through them without colliding (phantom objects don't trigger

collisions), another useful function is llVolumeDetect(), which can make the object phantom but still

trigger collision events when something enters the object.

llVolumeDetect(integer detect)

If detect is TRUE, the object becomes phantom but triggers collision_start() and

collision_end() events when other objects enter or leave the object. It will not trigger

collision() events. When FALSE, the object does not become phantom and thus can trigger all

three event types: collision(), collision_start(), and collision_end()

*

. This function

must appear in the root prim.

detect — Enables or disables phantom collision detection.

* The FALSE case makes nonphysical objects react to collisions as if they were physical. While useful, this

is undocumented behavior, so be careful if you use this feature.

DEFINITION

In comparison to llSensorRepeat(), the volume detector is a lot less expensive in terms of

computational resources, and you don't need to worry about delay. (The sensor may not catch an object if it

moves too quickly through the sensor zone.) You can use any arbitrary object (any shape, size, etc) to hold the

volume detector. That's cool because llSensorRepeat() will sense only in conical slices from spheres.

Whether the sensor or the volume detector is better for your situation depends on a variety of

factors. Table 5.3 summarizes the most common situations.