Video: Entities "Kickball" Tutorial walkthrough (55 minutes)
This tutorial project demonstrates basic Unity.Entities usage.
- Obstacles (grey cylinders) and players (orange capsules) are spawned on a field.
- Directional input moves the players, but players cannot walk through the obstacles.
- Hitting enter spawns a yellow ball at each player capsule's location.
- Hitting space kicks the balls that are near a player.
- The balls bounce off the obstacles and lose momentum over time.
The text below describes the general idea of each step, but you're strongly encouraged to study the code and read the comments.
In Step 1, the main scene contains an embedded 'sub scene', meaning a separate scene asset which is referenced by a SubScene MonoBehaviour in the main scene.
- At build time, the GameObjects in a sub scene are baked into entities that are serialized.
- When the main scene is loaded at runtime, the serialized entities are loaded along with the GameObjects of the main scene.
- The GameObjects of the sub scene are NOT loaded at runtime!
In the Step 1 scene, the sub scene contains a rendered plane GameObject for the ground "Plane" and an un-rendered GameObject called "Config" which has the ConfigAuthoring MonoBehaviour. Again, be clear that the GameObjects of the sub scene will not be loaded at runtime: the plane you see rendered in play mode is an entity, not a GameObject.
In baking, ConfigAuthoring adds a Config component to the baked entity. This Config component stores an assortment of game parameters, such as how many obstacles and players to spawn, plus the entity prefabs that we'll instantiate at runtime.
At the start of play mode, the ObstacleSpawnerSystem creates instances of the obstacle prefab. Because spawning should only happen once, the system disables itself to stop subsequent updates.
After the obstacles are spawned, the PlayerSpawnerSystem creates instances of the player prefab, one next to each obstacle.
Each frame, the PlayerMovementSystem reads the player's directional input and moves all of the players accordingly. Using a simple radius collision check, players are prevented from penetrating into the obstacles.
When the user hits the enter key, the BallSpawnerSystem spawns a ball at the location of each player with an initial velocity.
Every frame, the BallMovementSystem moves each ball based on its current velocity, deflects the velocity if the ball hits an obstacle, and diminishes the velocity over time.
When the user hits the space key, the BallKickingSystem applies an impact velocity to all balls within a short distance from a player.
These new systems duplicate the functionality of the originals, but they do the heavy lifting in jobs rather than on the main thread.
Note that the BallMovementJob and BallKickingJob both have the same query, so it might be more optimal if they were combined into one job, but this is just speculation. In practice, you should profile carefully to see whether consolidating them is actually faster!
Also note that when we schedule the IJobEntity jobs, we write:
myJob.ScheduleParallel(); ...but these schedule calls are modified by source-gen to pass and return a job handle:
state.Dependency = myJob.ScheduleParallel(state.Dependency); // result of source-genThis is necessary to correctly handle entity job dependencies, as explained here.
END OF TUTORIAL