Dynamic Navmesh: AI in the Dynamic Environment of Splinter Cell: Conviction

Splinter Cell: ConvictionUbisoft Montréal

Martin Walsh

Dynamic Environment

Lots of objectsExplosionsLots of NPCsDynamic Traps

AI

React

Interact

Navigate

Overview

CompareDevelopmentProblemsCool Features

Current Solutions

Grid-based

Two-tiered

Two-Tiered Solutions

Detailed Inconsistent

Why a Dynamic Navmesh?

One-tier solution

NPCs instantly aware

Dynamic Cover 1

Dynamic Cover 2

Blocked Paths

Overview

CompareDevelopmentProblemsCool Features

What is a Dynamic Navmesh?

Navmesh

2D representation of a 3D world• Triangles• Vertices• Edges• Walkable area• Extra information

What Makes it Dynamic

Modified in real timeFast Robust

Basic Operations

Adding

Removing

Adding an Object : Take 1

Cutting a hole

Adding an Object -- In Action

Adding an Object -- Paradigm

Rip out a chunkCut the holeReplug the new chunks

Adding an Object -- Pipeline

Get Object Contour

Get Affected Navmesh Contours

Combine Contours and Retessellate

Plug Triangles into Navmesh

Bounding volume

Points of Volume

Points projected onto X-Y plane

Convex hull

Expanded convex hull

Retessellated Navmesh

Get Affected Navmesh Contours

Find affected TrianglesMake Homogeneous contours

Combine Contours and Retessellate

CSG OperationTessellator

Plug Triangles into Navmesh

Will match up vertex for vertexNo floating point comparisonsVertex poolsLocal border recalculation

Removing an Object

How can you plug up a hole?

Removing an Object: Take 1

Use “Undo” to remove object

Removing an Object: Take 2

Undoing is free but redoing is expensive

What about subdividing?

Removing an Object: Take 3

But first…

Adding an Object: Take 2

How do you add an object so that you can remove it later?

Hole vs. Patch

Loss of information (Hole) Information retained (Patch)

Removing an Object: Take 3

Un-tag affected “Patch” triangles

Vertex clean-up

Overview

CompareDevelopmentProblemsCool Features

Plugging Problem

Vertex too close to edge of contour

Floating point imprecision

Degenerate Triangles

Produced by tessellator (or bad input)Bad for Robustness

Output Modification

Angle-optimal triangulation

Worked at first…

Degenerate Triangles Return

Stressing the system exposed problems

Degenerate faces

Input modification

Control your intersection vertices

Use vertex welding

Robustness Recap

Input/output modificationAvoid floating point comparisonControl your vertices

Performance Recap

LocalizePoolPartitionThread

Overview

CompareDevelopmentProblemsCool Features

The “Patch” system

Allows for new solutions to AI problems

Getting Stuck

Getting Unstuck

Interaction Based on State

Patrol• Avoid small obstacles

• Open doors

Combat• Plow through small obstacles• Bash doors

Guard and Civilians

Don’t Be Omniscient

Blocked door

The Future

Full 3D navigation

Bridges

martin.walsh@ubisoft.com

www.creatorsofemotions.com

Questions and AnswersDynamic Navmesh: AI in the Dynamic Environment of Splinter Cell: Conviction