using System.Diagnostics;
public partial class AsteroidSpawnSystem : SystemBase
//This will be our query for Asteroids
private EntityQuery m_AsteroidQuery;
//We will use the BeginSimulationEntityCommandBufferSystem for our structural changes
private BeginSimulationEntityCommandBufferSystem m_BeginSimECB;
//This will be our query to find GameSettingsComponent data to know how many and where to spawn Asteroids
private EntityQuery m_GameSettingsQuery;
//This will save our Asteroid prefab to be used to spawn Asteroids
protected override void OnCreate()
//This is an EntityQuery for our Asteroids, they must have an AsteroidTag
m_AsteroidQuery = GetEntityQuery(ComponentType.ReadWrite<AsteroidTag>());
//This will grab the BeginSimulationEntityCommandBuffer system to be used in OnUpdate
m_BeginSimECB = World.GetOrCreateSystem<BeginSimulationEntityCommandBufferSystem>();
//This is an EntityQuery for the GameSettingsComponent which will drive how many Asteroids we spawn
m_GameSettingsQuery = GetEntityQuery(ComponentType.ReadWrite<GameSettingsComponent>());
//This says "do not go to the OnUpdate method until an entity exists that meets this query"
//We are using GameObjectConversion to create our GameSettingsComponent so we need to make sure
//The conversion process is complete before continuing
RequireForUpdate(m_GameSettingsQuery);
protected override void OnUpdate()
//Here we set the prefab we will use
if (m_Prefab == Entity.Null)
//We grab the converted PrefabCollection Entity's AsteroidAuthoringComponent
//and set m_Prefab to its Prefab value
m_Prefab = GetSingleton<AsteroidAuthoringComponent>().Prefab;
//we must "return" after setting this prefab because if we were to continue into the Job
//we would run into errors because the variable was JUST set (ECS funny business)
//comment out return and see the error
//Because of how ECS works we must declare local variables that will be used within the job
//You cannot "GetSingleton<GameSettingsComponent>()" from within the job, must be declared outside
var settings = GetSingleton<GameSettingsComponent>();
//Here we create our commandBuffer where we will "record" our structural changes (creating an Asteroid)
var commandBuffer = m_BeginSimECB.CreateCommandBuffer();
//This provides the current amount of Asteroids in the EntityQuery
var count = m_AsteroidQuery.CalculateEntityCountWithoutFiltering();
//We must declare our prefab as a local variable (ECS funny business)
var asteroidPrefab = m_Prefab;
//We will use this to generate random positions
var rand = new Unity.Mathematics.Random((uint)Stopwatch.GetTimestamp());
for (int i = count; i < settings.numAsteroids; ++i)
// this is how much within perimeter asteroids start
// we are going to have the asteroids start on the perimeter of the level
// choose the x, y, z coordinate of perimeter
// so the x value must be from negative levelWidth/2 to positive levelWidth/2 (within padding)
var xPosition = rand.NextFloat(-1f*((settings.levelWidth)/2-padding), (settings.levelWidth)/2-padding);
// so the y value must be from negative levelHeight/2 to positive levelHeight/2 (within padding)
var yPosition = rand.NextFloat(-1f*((settings.levelHeight)/2-padding), (settings.levelHeight)/2-padding);
// so the z value must be from negative levelDepth/2 to positive levelDepth/2 (within padding)
var zPosition = rand.NextFloat(-1f*((settings.levelDepth)/2-padding), (settings.levelDepth)/2-padding);
//We now have xPosition, yPostiion, zPosition in the necessary range
//With "chooseFace" we will decide which face of the cube the Asteroid will spawn on
var chooseFace = rand.NextFloat(0,6);
//Based on what face was chosen, we x, y or z to a perimeter value
//(not important to learn ECS, just a way to make an interesting prespawned shape)
if (chooseFace < 1) {xPosition = -1*((settings.levelWidth)/2-padding);}
else if (chooseFace < 2) {xPosition = (settings.levelWidth)/2-padding;}
else if (chooseFace < 3) {yPosition = -1*((settings.levelHeight)/2-padding);}
else if (chooseFace < 4) {yPosition = (settings.levelHeight)/2-padding;}
else if (chooseFace < 5) {zPosition = -1*((settings.levelDepth)/2-padding);}
else if (chooseFace < 6) {zPosition = (settings.levelDepth)/2-padding;}
//we then create a new translation component with the randomly generated x, y, and z values
var pos = new Translation{Value = new float3(xPosition, yPosition, zPosition)};
//on our command buffer we record creating an entity from our Asteroid prefab
var e = commandBuffer.Instantiate(asteroidPrefab);
//we then set the Translation component of the Asteroid prefab equal to our new translation component
commandBuffer.SetComponent(e, pos);
//We will now set the PhysicsVelocity of our asteroids
//here we generate a random Vector3 with x, y and z between -1 and 1
var randomVel = new Vector3(rand.NextFloat(-1f, 1f), rand.NextFloat(-1f, 1f), rand.NextFloat(-1f, 1f));
//next we normalize it so it has a magnitude of 1
//now we set the magnitude equal to the game settings
randomVel = randomVel * settings.asteroidVelocity;
//here we create a new VelocityComponent with the velocity data
var vel = new PhysicsVelocity{Linear = new float3(randomVel.x, randomVel.y, randomVel.z)};
//now we set the velocity component in our asteroid prefab
commandBuffer.SetComponent(e, vel);
//This will add our dependency to be played back on the BeginSimulationEntityCommandBuffer
m_BeginSimECB.AddJobHandleForProducer(Dependency);