Physics with Bullet - jMonkeyEngine 3.0 - page 406

9. Now, we create another Node , which will be our thruster. Give it the name
Thruster to be able to identify it more easily later, as follows:
Node thruster = new Node("Thruster");
10. We set localTranslation of this so that it will end up at the bottom of the
spaceship, as shown in the following line of code:
thruster.setLocalTranslation(0, -1, 0);
11. Then, we attach it to the spaceShip node.
12. Now, we have to attach the spaceShip node to both the rootNode and
physicsSpace of bulletAppState .
13. To control the thruster and make it more reusable, we will create a class called
ThrusterControl , extending AbstractControl .
14. It'll have one field, a Spatial field called thruster , that will store the
thruster node.
15. We will override the setSpatial method and set it by calling
getChild("Thruster") on the supplied spatial.
16. Lastly, we define a new method called fireBooster() .
17. Inside this, we subtract the thruster's location from the spaceship's location and
store it in a new Vector3f field called direction as follows:
Vector3f direction =
spatial.getWorldTranslation().subtract(thruster.getWorldTranslation());
18. Then, we find the RigidBodyControl class in the spatial and call applyIm-
pulse with the direction vector. We use the inverted direction as the relative po-
sition that the impulse should originate from. This can be implemented as fol-
lows:
spatial.getControl(RigidBodyControl.class).applyImpulse(direction,
direction.negate());
19. In the application class, we have to make it call the fireBooster method. We
do this in the onAnalog method that was added when we implemented the An-
alogListener interface:
if(name.equals("boost") && value > 0){