Behavioral animation

CSE 3541Matt Boggus

Material recap and trajectory

• Geometric– Artist specifies translation and rotation over time

• Physically based– Artist specifies forces acting on objects– Motion equations dictate movement

• Behavioral– Artist directs autonomous agents

• Interpolation– Artist draws the scene at the beginning and end of a an

interval of time– Intermediate positions are calculated

Behavioral Animation

• Control the motion of one or more objects using virtual actors

• Goal: realistic or believable motion so that the object appears to be autonomous

• Matt Lewis’ page on BA http://accad.osu.edu/~mlewis/Class/behavior.html

Behavioral animation

• Character or object motion based on:

– Knowledge of the environment– Aggregate behavior– Primitive behavior– Intelligent behavior– Crowd management

Actor properties (position only)

Position (x, y)

Goal (xg, yg)

V = Goal - Position

Next Position = Position + V * dt

Actor properties (position and orientation)

Position (x, y)

Goal (xg, yg)

Vtarget = Goal - Position

Orientation (ox, oy) = transform.forward

Rotate(θ)

In Unity, you can use RotateTowards()

Rotate(-θ)Determine which rotation (±θ) orients the actor closer to the goal using dot product

Sample codeclass OrientedAgent2D {

// DataVector3 position;GameObject model; // Use this for geometry and orientation

// MethodsUpdate(float deltaTime);TurnLeft();TurnRight();MoveForward();MoveBackward();

};

Knowing the environment

•Vision and other senses– Information available now

•Memory– Information stored from the past

Vision

•General vision– What can the actor see? – What is everything in sight now?•Targeted vision– Can the actor see object X?

• Computation vs. accuracy– How much of an object needs to be seen to be

identified?– Do we need to model visual perception?

Omniscience

Everything in the scene is known

Field of view

Field of view – example

Orientation Vector (O)

Vector from agent to vertex (V)

Inside the cone when the angle between O and V is less then or equal to θ/2

Angle of cone = θ

Field of view – sample code

Vector3 agentPosition, orientation, objectPosition;float visionLimit;

Vector3 agentToVertex = objectPosition – agentPosition;

agentToVertex.Normalize();if(Vector3.Dot(agentToVertex,orientation) > visionLimit)

// agent can see object

Occluded Vision

Ray casting with collision detectionSample the environment

Target-testing vision (per object)

Can the actor see X?Cast a ray

How well can the actor see X?Use multiple rays

Target-testing vision (alternative)Sample the vision cone

Cast multiple rays

Lab4 – predator-prey simulation

•Unbalanced abilities– Vision

• Distance• Field of view

– Linear speed (moving forward)– Angular or rotational speed (turning)

Spatial Occupancy

Other senses

•Hearing•Smell

•Sensors & signal propagation•Spatial occupancy approach•Applications

Memory

•What is recorded about the environment

•Spatial occupancy

•Transience of objects: time-stamps

•Memory hierarchy: short-term, long-term

Spatial Occupancy

doorway

doorway

transiency

wal

l

Aggregate Behavior:Emergent Behavior

Type Elements Physics

Env/Others

Intelligence

Particles 102-104 Much/none None

Flocking 101-103 Some/some Limited

Crowds 101-102 Little/much Little-much

Typical qualities

Emergent behavior

• Complex systems and patterns arising out of simple rules

• Aints – AI ants http://www.youtube.com/watch?v=rsqsZCH36Hk

Predator Prey vision anatomy

Prey-Predator (vision)

Prey-Predator (movement – speed and turning)

Motion – force based

Apply a force on the predator towards the prey when in view

Force = c * posprey - pospred

Motion – kinematic based

Determine the closest prey in view then turn towards it and increase forward velocity

voldvnew

Prey-Predator – environment forces

Using pure forcesMay not prevent object penetrationPrey can be ‘hidden’ by environmental repulsive forces

Flocking, Swarming, Flying

Boidshttp://www.red3d.com/cwr/boids/

Local control

Rules defined to stay with friends, but avoid bumping into each other

Need additional rules for collision avoidance with obstacles

Local information

Other flocking issues•Global control– script flock leader– global migratory urge

•Negotiating the motion– Separation, alignment, and cohesion may compete/contradict

•Collision avoidance– Once an object is in sight, start steering to avoid

•Splitting and rejoining (difficult)– Collision avoidance too strong – flock may never rejoin after split– Flock membership too strong – flock does not split and formation changes

•Modeling flight

Negotiating the motion

ForcesOr “Reasoning”(e.g. rule-based)

Navigating obstacles

Problems with repulsive forces

Navigating using bounding sphere

NavigatingTesting for being on a collision path with

(bounding) sphere

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PCs

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Given: P, V, C, r

Finding closest non-colliding point

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PC

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Calculate s,t

Modeling flight – common in flocking

Modeling flight

Geometric flight – dynamic, incremental rigid transformation of an object moving along a tangent to a three dimensional curve

Modeling Flight – Lift

Air passing above wing most travel longer than air below it. Less pressure above wing = lift

Modeling Flight – turn by rolling

Modeling Flight – summary

• Turning is effected by horizontal lift

• Increasing pitch increases drag

• Increasing speed increases lift