Error when using setKinematic(true)!

In tutorials jMonkeyEngine has a code of Physics that has up to a brick wall to be knocked down, so I thought: If the ground that supports the bricks should not be affected by any force rather than creation with mass 0, I’ll try to make it does a Kinematic object, which is for this purpose. But when running the code bricks simply cross the floor. What is wrong?

I have a piece of string in my hand. How long is it?


Your answers help me a lot. ‘-’

package jme3test.helloworld;

import com.jme3.asset.TextureKey;
import com.jme3.bullet.BulletAppState;
import com.jme3.bullet.control.RigidBodyControl;
import com.jme3.font.BitmapText;
import com.jme3.input.MouseInput;
import com.jme3.input.controls.ActionListener;
import com.jme3.input.controls.MouseButtonTrigger;
import com.jme3.material.Material;
import com.jme3.math.Vector2f;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.shape.Box;
import com.jme3.scene.shape.Sphere;
import com.jme3.scene.shape.Sphere.TextureMode;
import com.jme3.texture.Texture;
import com.jme3.texture.Texture.WrapMode;

 * Example 12 - how to give objects physical properties so they bounce and fall.
 * @author base code by double1984, updated by zathras
public class HelloPhysics extends SimpleApplication {

  public static void main(String args[]) {
    HelloPhysics app = new HelloPhysics();

  /** Prepare the Physics Application State (jBullet) */
  private BulletAppState bulletAppState;

  /** Prepare Materials */
  Material wall_mat;
  Material stone_mat;
  Material floor_mat;

  /** Prepare geometries and physical nodes for bricks and cannon balls. */
  private RigidBodyControl    brick_phy;
  private static final Box    box;
  private RigidBodyControl    ball_phy;
  private static final Sphere sphere;
  private RigidBodyControl    floor_phy;
  private static final Box    floor;

  /** dimensions used for bricks and wall */
  private static final float brickLength = 0.48f;
  private static final float brickWidth  = 0.24f;
  private static final float brickHeight = 0.12f;

  static {
    /** Initialize the cannon ball geometry */
    sphere = new Sphere(32, 32, 0.4f, true, false);
    /** Initialize the brick geometry */
    box = new Box(Vector3f.ZERO, brickLength, brickHeight, brickWidth);
    box.scaleTextureCoordinates(new Vector2f(1f, .5f));
    /** Initialize the floor geometry */
    floor = new Box(Vector3f.ZERO, 10f, 0.1f, 5f);
    floor.scaleTextureCoordinates(new Vector2f(3, 6));

  public void simpleInitApp() {
    /** Set up Physics Game */
    bulletAppState = new BulletAppState();

    /** Configure cam to look at scene */
    cam.setLocation(new Vector3f(0, 4f, 6f));
    cam.lookAt(new Vector3f(2, 2, 0), Vector3f.UNIT_Y);
    /** Add InputManager action: Left click triggers shooting. */
            new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
    inputManager.addListener(actionListener, "shoot");
    /** Initialize the scene, materials, and physics space */

   * Every time the shoot action is triggered, a new cannon ball is produced.
   * The ball is set up to fly from the camera position in the camera direction.
  private ActionListener actionListener = new ActionListener() {
    public void onAction(String name, boolean keyPressed, float tpf) {
      if (name.equals("shoot") && !keyPressed) {

  /** Initialize the materials used in this scene. */
  public void initMaterials() {
    wall_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    TextureKey key = new TextureKey("Textures/Terrain/BrickWall/BrickWall.jpg");
    Texture tex = assetManager.loadTexture(key);
    wall_mat.setTexture("ColorMap", tex);

    stone_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    TextureKey key2 = new TextureKey("Textures/Terrain/Rock/Rock.PNG");
    Texture tex2 = assetManager.loadTexture(key2);
    stone_mat.setTexture("ColorMap", tex2);

    floor_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    TextureKey key3 = new TextureKey("Textures/Terrain/Pond/Pond.jpg");
    Texture tex3 = assetManager.loadTexture(key3);
    floor_mat.setTexture("ColorMap", tex3);

  /** Make a solid floor and add it to the scene. */
  public void initFloor() {
    Geometry floor_geo = new Geometry("Floor", floor);
    floor_geo.setLocalTranslation(0, -0.1f, 0);
    /* HERE MY ASK! */
    floor_phy = new RigidBodyControl();
    floor_phy.setKinematic(true); // THIS

  /** This loop builds a wall out of individual bricks. */
  public void initWall() {
    float startpt = brickLength / 4;
    float height = 0;
    for (int j = 0; j < 15; j++) {
      for (int i = 0; i < 6; i++) {
        Vector3f vt =
         new Vector3f(i * brickLength * 2 + startpt, brickHeight + height, 0);
      startpt = -startpt;
      height += 2 * brickHeight;

  /** This method creates one individual physical brick. */
  public void makeBrick(Vector3f loc) {
    /** Create a brick geometry and attach to scene graph. */
    Geometry brick_geo = new Geometry("brick", box);
    /** Position the brick geometry  */
    /** Make brick physical with a mass > 0.0f. */
    brick_phy = new RigidBodyControl(2f);
    /** Add physical brick to physics space. */

  /** This method creates one individual physical cannon ball.
   * By defaul, the ball is accelerated and flies
   * from the camera position in the camera direction.*/
   public void makeCannonBall() {
    /** Create a cannon ball geometry and attach to scene graph. */
    Geometry ball_geo = new Geometry("cannon ball", sphere);
    /** Position the cannon ball  */
    /** Make the ball physcial with a mass > 0.0f */
    ball_phy = new RigidBodyControl(1f);
    /** Add physical ball to physics space. */
    /** Accelerate the physcial ball to shoot it. */

  /** A plus sign used as crosshairs to help the player with aiming.*/
  protected void initCrossHairs() {
    guiFont = assetManager.loadFont("Interface/Fonts/Default.fnt");
    BitmapText ch = new BitmapText(guiFont, false);
    ch.setSize(guiFont.getCharSet().getRenderedSize() * 2);
    ch.setText("+");        // fake crosshairs :)
    ch.setLocalTranslation( // center
      settings.getWidth() / 2 - guiFont.getCharSet().getRenderedSize() / 3 * 2,
      settings.getHeight() / 2 + ch.getLineHeight() / 2, 0);

Like I said, when you run this code, the blocks just fall and cross the floor

1 Like

You never set any mass for the floor, the empty constructor is not meant to be used.

Ok, I did not realize it

object with mass 0 = optimized to be an non moving “force immune” object
kinematics = optimized to be an moving “force immune” object
rigid body = moving non immune to forces object

so what is more precise ?

mass0 > kinematics > rigidbody

What is your doubt about it ?

Damn, a lot of people are doing this mistake. Do not make an object kinematic just because it is not going to move. Just set it’s mass to 0 and use kinematic for moving objetcs, like @wagfeliz said.