SteeringSystem.java

package com.gdxjam.systems;

import com.badlogic.ashley.core.Entity;
import com.badlogic.ashley.core.Family;
import com.badlogic.ashley.systems.IteratingSystem;
import com.badlogic.gdx.ai.steer.SteeringAcceleration;
import com.badlogic.gdx.ai.steer.SteeringBehavior;
import com.badlogic.gdx.math.Vector2;
import com.badlogic.gdx.physics.box2d.Body;
import com.gdxjam.GameManager;
import com.gdxjam.components.Components;
import com.gdxjam.components.SteerableComponent;
import com.gdxjam.components.SteeringBehaviorComponent;

public class SteeringSystem extends IteratingSystem {

	private static final SteeringAcceleration<Vector2> steeringOutput = new SteeringAcceleration<Vector2>(new Vector2());

	public SteeringSystem() {
		super(Family.all(SteeringBehaviorComponent.class).one(SteerableComponent.class).get());
	}

	@Override
	protected void processEntity(Entity entity, float deltaTime) {
		SteeringBehavior<Vector2> behavior = Components.STEERING_BEHAVIOR.get(entity).getBehavior();
		SteerableComponent steerable = Components.STEERABLE.get(entity);

		if (behavior == null)
			return;
		if (steerable.getBody() == null)
			return; // We shouldn't need this
		behavior.calculateSteering(steeringOutput);
		boolean anyAccelerations = false;
		Body body = steerable.getBody();

		if (!steeringOutput.linear.isZero()) {
			Vector2 force = steeringOutput.linear.scl(deltaTime);
			body.applyForceToCenter(force, true);
			anyAccelerations = true;
		}

		// Update orientation and angular velocity
		if (steerable.isIndependentFacing()) {
			if (steeringOutput.angular != 0) {
				body.applyTorque(steeringOutput.angular * deltaTime, true);
				anyAccelerations = true;
			}
		}

		else {
			// If we haven't got any velocity, then we can do nothing.
			Vector2 linVel = body.getLinearVelocity();
			if (!linVel.isZero(steerable.getZeroLinearSpeedThreshold())) {
				float newOrientation = steerable.vectorToAngle(linVel);
				body.setAngularVelocity((newOrientation - steerable.getAngularVelocity()) * deltaTime); // this
																			// is
																			// superfluous
																			// if
																			// independentFacing
																			// is
																			// always
																			// true
				body.setTransform(body.getPosition(), newOrientation);
			}
		}

		if (anyAccelerations) {
			// Cap the linear speed
			Vector2 velocity = body.getLinearVelocity();
			float currentSpeedSquare = velocity.len2();
			float maxLinearSpeed = steerable.getMaxLinearSpeed();
			if (currentSpeedSquare > maxLinearSpeed * maxLinearSpeed) {
				body.setLinearVelocity(velocity.scl(maxLinearSpeed / (float) Math.sqrt(currentSpeedSquare)));
			}

			// Cap the angular speed
			float maxAngVelocity = steerable.getMaxAngularSpeed();
			if (body.getAngularVelocity() > maxAngVelocity) {
				body.setAngularVelocity(maxAngVelocity);
			}
		}
	}

	@Override
	public boolean checkProcessing() {
		return !GameManager.isPaused();
	}

}