MOTION PLANNING IN REAL AND VIRTUAL ENVIRONMENTSFALL 2007

Second Life: Second Life: IntroductionIntroduction

Russell GayleComp 790-058 – Robot Motion Planning

Fall 2007

September 24, 2007

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

What is Second Life?

• The Grid: The hardware behind the SL Metaverse

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

What is Second Life?

• The Grid is organized into Simulators » Single server instances

Simulators

Isle 2 Isle 3

Isle 6Isle 5Isle 4

Isle 1

Connecting to Isle 1

Side connections to adjacent simulators

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

What is Second Life?

• Simulators are where the real work happens» Each simulator is responsible for its avatars

Isle 1

Communications (chat/IM)Physical State, Collisions

InventoryAnimationsSL Identifier

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

What is Second Life?

• Simulators are where the real work happens» Each simulator stores and distributes its prims

Isle 1

TransformationsTexturesPhysics

Embedded items

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

What is Second Life?

• Primitives can hold any type of object» Primitives, scripts, animations, sounds, etc

• LSL makes the world interactive» Embedded into prims

LSL ScriptsChange primitive appearanceInteract with other primitives

Interact with avatarsPhysics

Query remote resourcesMany more!

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

What’s missing?What’s missing?

• Important features of SL that we will not cover» Economy

• Linden Dollars• Content creation • and IP rights• Land ownership

» In world attractions• Virtual sightseeing• “Live” music

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

The Grid

• Collectively can be considered “The World”» A large array of Debian servers

• Each server can support several simulations

» Centralized network topology• All communications goes through the Grid

» Beta Grid: A test bed for upcoming technologies

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Simulators

• Also referred to as a Region» e.g. Natoma, UNC CH I, UNC CH II

• Typically has a dedicated CPU• Each region is 256 m by 256 m

» Larger islands are made by connecting several regions

• Responsibilities» Geometry / Prims

» Avatars

» Local messaging (whisper, say, shout)

» Voice-chat

» Client-server networking

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

SimulatorsSimulators

• SLUIDs» Every object (prims, avatars, animations,

audio, etc) has a (global) SL Unique ID number

» Each simulator also has local references to avatars and primitives

• Multi-simulator islands» In reality, connected to multiple island

simultaneously in case you cross borders

» Note: You may need to keep track of this in your work!

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Avatars

• Your virtual representation (or your bot’s)» Stored in a central database

• Important features» Appearance

• How you look

(height, clothing, etc)

» Inventory• What you can use

and what you can DO

• Local animations

• Local sounds

• Other primitives or scripts

» Communication» State and Motion

• Position, orientation, velocity, colliding, physics, etc

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Avatars: What they can doAvatars: What they can do

• Create primitives• Interact with (touch) primitives

» This often activates scripts

• Attach prims to themselves• Chat (whisper, say, shout)

» This can also activate scripts

• Navigate » Ground-based (walk, run)

» Air-based (fly) • Predefined animations

» Instant navigation (teleportation) • You may not always end up where you expect!

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Avatars: LimitationsAvatars: Limitations

• Precision» Not easy to reach a specific location

» Occasionally collisions are missed

• Bandwidth» Not always enough to update all objects

» May cause missed collisions or stalled motion

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Primitives

• Belongs to a Region (simulator)• 7 base types

» Box, cylinder, prism, sphere, torus, tube, ring

» All items built by transformations of these

• 1 special type» Sculpted prim

• Prim whose shape is determined by a “Sculpt Texture”

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

PrimitivesPrimitives

• Seven base material types» Stone, metal, glass, wood, flesh, plastic,

rubber

• Has several other state parameters» Physical

» Flexible (automatically non-physical)

» Texture

» Color

» Bumpiness

» Lighting

» Transparency

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Linden Script Language (LSL)

• Embedded in a prim (or a group of prims)» Not in avatars

» Each prim in a group can have a script

» Scripts between linked prims are faster

» All scripts in a prim are run

• Similar to C or Java • But with an emphasis on states and events

» Events trigger behaviors (functions)

» Can also cause a change of state

• And now for a crash course in LSL!

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

LSL: Getting StartedLSL: Getting Started

• Creating a script1. Open the prim “Create” menu

2. Select a prim

3. Find the contents of the prim

4. Select “Create a new script”

• The default script

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default {

state_entry() {

llSay(0, "Hello, Avatar!"); }

touch_start(integer total_number) {

llSay(0, "Touched."); }

}

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

LSL: StatesLSL: States

• State is used to determine which “behavior” should be used

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default //default state is mandatory {

state_entry() {

llSay(0, "turning on!"); llSetColor(<1.0, 1.0, 1.0>, ALL_SIDES);

}

touch_start(integer total_number) {

state off;}

}

state off {

state_entry() {

llSay(0, "turning off!"); llSetColor(<0.0, 0.0, 0.0>, ALL_SIDES);

}

touch_start(integer total_number) {

state default; }

}

Triggers a change of state

A new state

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

LSL: EventsLSL: Events

• We’ve seen two events» state_entry - When a state is activated

» touch_start – When an object is touched

• A few others which may be usefulat_target – when a prim reaches its target

collision – when a prim collides

http_response – response to http request (used when working with remote resources)

sensor – when a sensor call returns something

» Note: Sensors are useful for tracking and following

Documentation: http://wiki.secondlife.com/wiki/LSL_Portal

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Live Demo!Live Demo!

• Overview of the main features in Second Life

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SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

Introduction: Robots in SL

• Two varieties» LSL (primitives)

» Simulated network traffic (avatars)

• Tradeoffs» LSL is stored and run on the simulator (server-

side) • Only works with prims

» Network traffic is subject to missed packets and limited by client performance

• Note» Both can access remote utilities!

SL OVERVIEW

THE GRID

SIMULATORS

AVATARS

PRIMITIVES

SCRIPTING (LSL)

LIVE DEMO

INTRO: SL BOTS

LIBSecondLifeLIBSecondLife

• http://www.libsecondlife.org• Reverse engineering of SL network protocol

» Inspect, insert, or remove packets from the client

» Create your own client• We will control an autonomous avatar this way

• More of this next time

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