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DOTSoftheDead

DOTS of the Dead is a DOTS sample game project that's meant to be an example of "real gameplay" implemented fully in DOTS. It is a simple local-multiplayer top-down zombie shooter.

How to Play

On start, the game will automatically spawn one Player for the keyboard, and one more Player for each connected gamepad

Controls

• 1: spawn a wave of zombies (you can press this many times for more zombies)
• Escape: reset the game
• WASD/LeftStick: move
• IJKL/RIghtStick: aim
• Space/RightTrigger: Shoot
• LeftCTRL/LeftTrigger: Melee attack

Pickups

• Small red orbs are healthpacks
• White boxes increase your fire rate
• Red boxes add to your number of projectiles (but you need to pick up more and more of them to gain a bonus)

Overview of Implementation

Game Initialization

Game Initialization is handled in a Monobehaviour called GameInitializer in the game scene. This behaviour does the following on start:

• Convert all game prefabs to their Entity representation (characters, weapons, etc...)
• Spawn one player+character per input device
• Setup some data in the ZombieSpawningSystem, to make it ready to spawn batches

Player inputs

This is handled in PlayerInputSystem.

This system has a CreatePlayer function that spawns a Player entity, which holds a PlayerTag component, a GameplayInput component, and a buffer of associated input device IDs. It then uses the new input system’s callbacks to build arrays of all inputs with associated devices that were made during the frame. Finally, it launches a job whose purpose is to go fill the GameplayInput struct of each player with the inputs corresponding to the devices those players were given.

We end up with a bunch of Player entities who all have their GameplayInputs components up to date.

In order to use those inputs for character movement, weapon shooting, etc…. We use the OwningPlayer component in combination with jobs whose purpose is to give an entity the inputs it needs based on its owning player entity. An example of this is the PlayerInputsToCharacterInputsJob in CharacterMoveSystem. This job will, for each character with an OwningPlayer component, find the associated player entity and feed the player’s inputs into the character movement components

Character Movement

The character movement system, used both by player characters and zombies, has two main components: CharacterInputs and Character.

CharacterInputs stores the intention of the character: Move vector, look direction, whether we’re attacking or not.

Character stores the characteristics of the character: Move speed, move sharpness, orientation sharpness, etc….

CharacterMoveSystem launches a job that, for each <Character, CharacterInputs, PhysicsVelocity, Rotation> entities, will translate character inputs and character data into a velocity to apply to PhysicsVelocity, and a rotation to apply to Rotation CharacterCollisionSystem launches a ITriggerEventsJob, which is how trigger overlaps are processed. For each character-to-character trigger events, this job will apply a decollision impulse to both characters.

CharacterAnimationSystem handles making the character mesh entities bob up and down based on their current velocity

Zombies

Zombies are extremely simple, and require only the following systems.Each of those systems will launch a job that will iterate on every zombie, every frame.

AssignTargetClosestPlayerSystem finds the closest player to each zombie in a certain range, and assign them as it’s target AssignTargetRandomSystem if a zombie doesn’t have a player in it’s range as a target, this system will choose a location around the zombie, and use it as a target. This will be the zombie’s destination until it reaches it, or a player comes in it’s range.

MoveTowardTargetSystem moves every zombie toward its target, at full speed if it’s a player, slower (1/3) if not.

ZombieAutoAttackSystem if the zombie has a player target and is close enough, it will change its AttackInputs so that a melee attack will be triggered

Weapons

Weapons are assigned to the corresponding character when it is spawned. A melee weapon is assigned to the zombies, and both a range and melee weapon is assigned to the player

AttackSystem launches 4 jobs:

• PlayerInputsToRangeWeaponInputsJob feeds player inputs to weapon
• PlayerInputsToMeleeWeaponInputsJob feeds player inputs to weapon
• WeaponShootJob tests for every range weapon if the shoot input is held, and spawn a bullet if needed
• MeleeAttackJob same thing but for melee weapons

Camera

The Camera is a bit special because it’s not yet converted automatically to a DOTS entity. We use an orthographic Camera and the goal is to be able to move it and change its orthographic size so we can see all the players at the same time on screen.

First, a monobehaviour CameraManager is in charge of creating the camera entity and its main component CameraData.

Also, there is another monobehaviour CameraEntityBridge. It makes the bridge between the entity and the monobehaviour world, by setting the values of the CameraData component and getting the Translation from the entity to place the GameObject in the world.

Two entities are actually used for the camera, one for the pivot gameobject and one for the actual Camera gameobject (a system uses its world position in the entity world) To be able to focus the camera any number of entities, a CameraFocus component is assigned to the entities.

The CameraFocusSystem launches a job that gets the position of all entities with the CameraFocus component and uses them to set the position and the orthographic size of the camera.

To get those, it uses an EntityQuery which retrieve the entities with a CameraFocus and Translation component.

The BillboardSystem launches a IJobForEach<Billboard, LocalToWorld, Rotation, Translation, Parent>, making every entity with a Billboard component face the camera.

Pickups

PickUps are prefabs transformed into entities by the GameInitializer. There are two types : some are moving toward the player, others are static and the player needs to get to them to collect them.

The Health pickups are attracted to the player in a certain radius. For this, they just have the MoveToTarget and FollowingPickUp component added to them. The MoveTowardTargetSystem launches an additional job for the entities with FollowingPickUp component because they have a configurable speed.

The PickupSystem launches an ITriggerEventsJob for each type of pickup, foreach player-pickup event, the modifications to the corresponding player character components are done.

The pickup also use the DestroyAfterTime component which is used by the DestroyAfterTimeSystem jobs to destroy entities after a certain time.