JavaECS/examples/misc/PhysicsSystem.java

package nz.ac.massey.javaecs;

public class PhysicsSystem extends ECSSystem{
    ECS gameEngine;
    public PhysicsSystem(ECS gameEngine){
        this.gameEngine = gameEngine;
    }

    @Override
    void init() {}

    @Override
    void update() {}

    void update(Double dt){
        for (Integer entity : entities) {
            Vec2D pos = (Vec2D)gameEngine.getComponentData(entity, Vec2D.class);
            RidgidBody ridgidBody = (RidgidBody)gameEngine.getComponentData(entity, RidgidBody.class);
            Gravity gravity = (Gravity)gameEngine.getComponentData(entity, Gravity.class);
            // Firstly, add the result of the accelerative forces to the ridgidbody
            ridgidBody.xdot += ridgidBody.xAcc * dt;
            ridgidBody.ydot += ridgidBody.yAcc * dt;
            
            // Special case of gravity
            if (gravity.terminalX < 0 || Math.abs(ridgidBody.xdot) < gravity.terminalX){
                ridgidBody.xdot += gravity.x * dt;
            }
            if (gravity.terminalY < 0 || Math.abs(ridgidBody.ydot) < gravity.terminalY){
                ridgidBody.ydot += gravity.y * dt;
            }
            
            // Finally, move the vec2d by the new velocity
            pos.x += ridgidBody.xdot * dt;
            pos.y += ridgidBody.ydot * dt;
        }
    }
}