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?
3 Likes
Your answers help me a lot. ‘-’
package jme3test.helloworld;
import com.jme3.app.SimpleApplication;
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();
app.start();
}
/** 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);
sphere.setTextureMode(TextureMode.Projected);
/** 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));
}
@Override
public void simpleInitApp() {
/** Set up Physics Game */
bulletAppState = new BulletAppState();
stateManager.attach(bulletAppState);
//bulletAppState.getPhysicsSpace().enableDebug(assetManager);
/** 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. */
inputManager.addMapping("shoot",
new MouseButtonTrigger(MouseInput.BUTTON_LEFT));
inputManager.addListener(actionListener, "shoot");
/** Initialize the scene, materials, and physics space */
initMaterials();
initWall();
initFloor();
initCrossHairs();
}
/**
* 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) {
makeCannonBall();
}
}
};
/** 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");
key.setGenerateMips(true);
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");
key2.setGenerateMips(true);
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");
key3.setGenerateMips(true);
Texture tex3 = assetManager.loadTexture(key3);
tex3.setWrap(WrapMode.Repeat);
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.setMaterial(floor_mat);
floor_geo.setLocalTranslation(0, -0.1f, 0);
this.rootNode.attachChild(floor_geo);
/* HERE MY ASK! */
floor_phy = new RigidBodyControl();
floor_phy.setKinematic(true); // THIS
floor_geo.addControl(floor_phy);
bulletAppState.getPhysicsSpace().add(floor_phy);
}
/** 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);
makeBrick(vt);
}
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);
brick_geo.setMaterial(wall_mat);
rootNode.attachChild(brick_geo);
/** Position the brick geometry */
brick_geo.setLocalTranslation(loc);
/** Make brick physical with a mass > 0.0f. */
brick_phy = new RigidBodyControl(2f);
/** Add physical brick to physics space. */
brick_geo.addControl(brick_phy);
bulletAppState.getPhysicsSpace().add(brick_phy);
}
/** 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);
ball_geo.setMaterial(stone_mat);
rootNode.attachChild(ball_geo);
/** Position the cannon ball */
ball_geo.setLocalTranslation(cam.getLocation());
/** Make the ball physcial with a mass > 0.0f */
ball_phy = new RigidBodyControl(1f);
/** Add physical ball to physics space. */
ball_geo.addControl(ball_phy);
bulletAppState.getPhysicsSpace().add(ball_phy);
/** Accelerate the physcial ball to shoot it. */
ball_phy.setLinearVelocity(cam.getDirection().mult(25));
}
/** A plus sign used as crosshairs to help the player with aiming.*/
protected void initCrossHairs() {
guiNode.detachAllChildren();
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);
guiNode.attachChild(ch);
}
}
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.