astro2049 / dead-island

Zombie apocalypse!

Dead Island

Scenario 2: Zombie Apocalypse

Environment: Ocean Islands

The scene is set on some connected ocean islands. A squad of survivors begins on one island and must navigate through zones populated with wandering zombies to reach a safe zone.

Playthrough Video https://youtu.be/tfhC5Rpoukg

0. Scene Overview (Unity)

• Canvas. Where the buttons at.
• Map. A container for tiles, ocean background etc.
• Game Manager. Holds LevelGenerator, GameManager, and the NavMeshSurface.
• UI. Legends and indicators.
• Music Player. Plays the background music. I added music only because it makes the gunfire sounds a lot less 'out of nowhere'...

1. Map Generation

Map Overview

• Playable area is a 64 * 64 tile grid, with each tile = 1.5 * 1.5m.

• Three types of tiles: Ocean (won't be rendered to scene), Beach, and Forest.

• Ocean islands generated with a binary space trees (BSP), a cellular automata (CA), and a post processor (I'll call it PP).

Generation Overview

The map starts out with all Ocean tiles public TileType[,] grid;.

Terminology: As we know the partition unit in BSP is "room", while in code "room" is class Island, so I might refer to "room" as "island" as well.

1. Partitioning. BSP partitions the map into rooms. Leaf rooms are recorded in the process.
2. Generate individual islands. For every leaf room,
   1. CA evolves the island landscape, starting with an initial 3 * 3 Forest tile square.
   2. PP generates the coastlines, by turning some Forest tiles on land edges (adjacent to the ocean) into Beach tiles.
3. Connect the islands. PP connects the islands, creating pathways between islands by writing the tiles along a direct line connecting the centers of each island 3 tiles wide, all to Beach/Forest tiles.
4. Render the tile grid to scene.
5. Build the nav mesh on the map.
6. Place survivors and zombies.

1.0 Generator Design

So, as mentioned before, there is a

• Binary space trees (BSP), class BinarySpaceTrees
  • And room/island, class Island
• Cellular automata (CA), class CellularAutomata
• Post processor (PP), class PostProcessor
• and, a level generator, which organizes the generation process, class LevelGenerator

1.0.0 Level Generator

public void Generate() fires up the generation.

1.0.1 Binary Space Trees (BSP)

Splits the map into rooms.

public void Partition(Island island)

Recursively partition the rooms.

• A leaf island is formed when width <= maxWidth || height <= maxHeight.
• If both width and height are bigger than max, there's a 50/50 chance of splitting horizontally/vertically.

private void SplitHorizontally(Island island)

private void SplitVertically(Island island)

Split an island horizontally/vertically. Initial split at the central line, and there's a m_splitWiggle = 12, which shifts the divider a bit.

1.0.2 Cellular Automata

Creates the actual landscape of an island.

private void InitializeIsland(Island island)

Set the center 3 * 3 tiles of an island to Forest tiles.

public void GenerateIsland(Island island)

private TileType GetNewState(int x, int y)

Evolve the initial tiles square: gradually expand the island landscape.

I made up the evolution rule: What's the new state for an Ocean cell? - If it has >= 3 land Moore neighbors, it has a 50% chance of becoming a Forest cell.

1.0.3 Post Processor

Generates coastlines for an island, and connects the islands.

public void GenerateCoastlines(Island island)

Given an island, generate its coastlines, by transforming some of the Forest tiles adjacent (or close) to water to Beach (Again, the algorithm is made-up, by me).

public void ConnectIslands(Island island)

Given the root island, connect the islands' centers. The direction is top-down, so we're connecting the largest rooms first and the leaf rooms last, as we are doing a depth-first search just like void BinarySpaceTrees::Partition(Island island).

2. Agents

Agents Overview

Agents,

• There are survivors and zombies
• have perceptions: visual, and aural
• act with behavior trees, using NPBehave
• all steering through NavMeshAgent
• in code, both derived from class IndividualAgent
• Survivors are in a squad, manager is class SquadAgent
• Prefabs next to scene (under Assets/Main.unity)

2.0 Individuals

2.0.0 Perceptions, class AIPerception

Visual

• Forward sight
• angle: 180 degrees
• distance: 10m
• Collision present: A collision rectangle (square)

Aural

• All-directional hearing
• angle: 360 degrees
• radius = 15m (zombies) / 7m (survivors)
• Collision present: A collision sphere (circle)

2.0.1 Individual Agents

Individual Agent, class IndividualAgent

m_targets, and m_target

An individual always maintains a list of enemies observed, in m_targets, and selects the closest enemy, as m_target.

(m_target won't be updated unless m_target cannot be sensed anymore/is dead. So while this is cool for zombies, it's indeed not that perfect for survivors)

Zombie, class ZombieAI : IndividualAgent

A zombie

• Roams at 2m/s. Picks a random location within a radius, goes there, waits, and repeats.
• When sees a survivor, chases at 8m/s.
  • If the survivor is within attack range = 3m, attacks.

Survivor, class SurvivorAI : IndividualAgent

A survivor

• Navigates at 5m/s if everything's fine
  • if is Leader, to the safe zone
  • or else, follow the leader
• If senses a zombie,
  • turn to face the zombie with angular speed = 360 deg/s
  • if is facing the target (<= 10 deg) and rifle is loaded (currentFireCooldown <= 0s), it shoots (cooldown = 1.2s)
  • else, and if the zombie is too close (<= 7m), back up to create some distance

2.1 The Squad

Squad Overview

• Survivors are organized in a squad.
• All survivors belong to a squad.
• Squad assigns roles.
• Individual survivors perform those roles.
• Roles are behaviors.
• There are two roles: Leader, and Follower.
• Leader's direction is squad's direction.
• Squad advances in formation.
• Leader navigates to the safe zone, while followers follow and maintain the formation.
• A squad member engages zombies upon spotting any and returns to formation if all targets are cleared.

More on Squad Coordination

New Leader

If the leader is dead, the last follower becomes the leader (if there are still followers).

Killing a Zombie

When a squad member kills a zombie, it is notified across the squad, other squad members will remove the zombie from m_targets, saving shots.

References

Cellular Automata

1. White Box Dev (2020) 'Cellular Automata | Procedural Generation | Game Development Tutorial', YouTube, 19 September. Available at: https://www.youtube.com/watch?v=slTEz6555Ts (Accessed 27 March 2024).

Binary Space Trees/Partitioning

2. 'Basic BSP Dungeon generation' (2023) RogueBasin. Available at: https://www.roguebasin.com/index.php/Basic_BSP_Dungeon_generation (Accessed 31 March 2024).

3. Sunny Valley Studio (2020) 'Binary Space Partitioning Algorithm - P13 - Unity Procedural Generation of a 2D Dungeon', YouTube, 19 December. Available at: https://www.youtube.com/watch?v=nbi88hY9hcw (Accessed 31 March 2024).

4. Uribe, G. (2019) 'Dungeon Generation using Binary Space Trees', Medium, 2 June. Available at: https://medium.com/@guribemontero/dungeon-generation-using-binary-space-trees-47d4a668e2d0 (Accessed 31 March 2024).

Ocean Texture

5. 'Shallow Ocean Terrain Texture' (2019) Don't Starve Wiki. Available at: https://dontstarve.fandom.com/wiki/Ocean?file=Shallow_Ocean_Terrain_Texture.png#Shipwrecked (Accessed 1 April 2024).

Unity Packages

6. Nilspferd (2019) NPBehave - Event Driven Code Based Behaviour Trees, v. 1.2.3. Available at: https://assetstore.unity.com/packages/tools/behavior-ai/npbehave-event-driven-code-based-behaviour-trees-75884 (Accessed 30 Jan 2024).

7. Alstra Infinite (2021) Planes & Choppers - PolyPack, v. 1.2. Available at: https://assetstore.unity.com/packages/3d/vehicles/air/planes-choppers-polypack-194946 (Accessed 9 April 2024).

8. Sound Earth Game Audio (2023) Post Apocalypse Guns Demo, v. 1.1.1. Available at: https://assetstore.unity.com/packages/audio/sound-fx/weapons/post-apocalypse-guns-demo-33515 (Accessed 11 April 2024).

9. Muz Station Productions (2017) FREE Energy Hard Rock Music Pack, v. 1.2. Available at: https://assetstore.unity.com/packages/audio/music/rock/free-energy-hard-rock-music-pack-54012 (Accessed 11 April 2024).

Squad Coordination

10. Karlsson, T. (2022) 'Squad Coordination in "Days Gone"', YouTube, 7 February. Available at: https://www.youtube.com/watch?v=7TQ-WS3MPlE (Accessed: 20 March 2024).