LiteCraft/src/main/java/io/github/hydos/ginger/engine/particle/ParticleSystem.java

package io.github.hydos.ginger.engine.particle;

import java.lang.Math;
import java.util.Random;

import org.joml.*;

import io.github.hydos.ginger.engine.io.Window;
import io.github.hydos.ginger.engine.math.Maths;

public class ParticleSystem
{
	private float pps, averageSpeed, gravityComplient, averageLifeLength, averageScale;
	private float speedError, lifeError, scaleError = 0;
	private boolean randomRotation = false;
	private Vector3f direction;
	private float directionDeviation = 0;
	private ParticleTexture texture;
	private Random random = new Random();

	public ParticleSystem(ParticleTexture texture, float pps, float speed, float gravityComplient, float lifeLength, float scale)
	{
		this.pps = pps / 100000;
		this.averageSpeed = speed;
		this.gravityComplient = gravityComplient;
		this.averageLifeLength = lifeLength;
		this.averageScale = scale;
		this.texture = texture;
	}

	/** @param direction - The average direction in which particles are emitted.
	 * @param deviation - A value between 0 and 1 indicating how far from the chosen direction particles can deviate. */
	public void setDirection(Vector3f direction, float deviation)
	{
		this.direction = new Vector3f(direction);
		this.directionDeviation = (float) (deviation * Math.PI);
	}

	public void randomizeRotation()
	{ randomRotation = true; }

	/** @param error
	 *              - A number between 0 and 1, where 0 means no error margin. */
	public void setSpeedError(float error)
	{ this.speedError = error * averageSpeed; }

	/** @param error
	 *              - A number between 0 and 1, where 0 means no error margin. */
	public void setLifeError(float error)
	{ this.lifeError = error * averageLifeLength; }

	/** @param error
	 *              - A number between 0 and 1, where 0 means no error margin. */
	public void setScaleError(float error)
	{ this.scaleError = error * averageScale; }

	public void generateParticles(Vector3f systemCenter)
	{
		float delta = (float) Window.getTime();
		float particlesToCreate = pps * delta;
		int count = (int) Math.floor(particlesToCreate);
		float partialParticle = particlesToCreate % 1;
		for (int i = 0; i < count; i++)
		{ emitParticle(systemCenter); }
		if (Math.random() < partialParticle)
		{ emitParticle(systemCenter); }
	}

	private void emitParticle(Vector3f center)
	{
		Vector3f velocity = null;
		if (direction != null)
		{
			velocity = generateRandomUnitVectorWithinCone(direction, directionDeviation);
		}
		else
		{
			velocity = generateRandomUnitVector();
		}
		velocity.normalize();
		Maths.scale(velocity, generateValue(averageSpeed, speedError));
		float scale = generateValue(averageScale, scaleError);
		float lifeLength = generateValue(averageLifeLength, lifeError);
		new Particle(texture, new Vector3f(center), velocity, gravityComplient, lifeLength, generateRotation(), new Vector3f(scale, scale, scale));
	}

	private float generateValue(float average, float errorMargin)
	{
		float offset = (random.nextFloat() - 0.5f) * 2f * errorMargin;
		return average + offset;
	}

	private float generateRotation()
	{
		if (randomRotation)
		{
			return random.nextFloat() * 360f;
		}
		else
		{
			return 0;
		}
	}

	private static Vector3f generateRandomUnitVectorWithinCone(Vector3f coneDirection, float angle)
	{
		float cosAngle = (float) Math.cos(angle);
		Random random = new Random();
		float theta = (float) (random.nextFloat() * 2f * Math.PI);
		float z = cosAngle + (random.nextFloat() * (1 - cosAngle));
		float rootOneMinusZSquared = (float) Math.sqrt(1 - z * z);
		float x = (float) (rootOneMinusZSquared * Math.cos(theta));
		float y = (float) (rootOneMinusZSquared * Math.sin(theta));
		Vector4f direction = new Vector4f(x, y, z, 1);
		if (coneDirection.x != 0 || coneDirection.y != 0 || (coneDirection.z != 1 && coneDirection.z != -1))
		{
			Vector3f rotateAxis = coneDirection.cross(coneDirection, new Vector3f(0, 0, 1));
			rotateAxis.normalize();
			float rotateAngle = (float) Math.acos(coneDirection.dot(new Vector3f(0, 0, 1)));
			Matrix4f rotationMatrix = new Matrix4f();
			rotationMatrix.rotate(-rotateAngle, rotateAxis);
			rotationMatrix.transform(direction, direction);
		}
		else if (coneDirection.z == -1)
		{ direction.z *= -1; }
		return Maths.Vec4ToVec3(direction);
	}

	private Vector3f generateRandomUnitVector()
	{
		float theta = (float) (random.nextFloat() * 2f * Math.PI);
		float z = (random.nextFloat() * 2) - 1;
		float rootOneMinusZSquared = (float) Math.sqrt(1 - z * z);
		float x = (float) (rootOneMinusZSquared * Math.cos(theta));
		float y = (float) (rootOneMinusZSquared * Math.sin(theta));
		return new Vector3f(x, y, z);
	}
}