setCcdMotionThreshold(0f)
介绍
连续碰撞检测（ccd）解决了子弹与纸张的问题。当一个快速移动的物体在一个时间步长内位于薄物体的一侧，在下一个时间步长内位于另一侧，导致物理引擎认为根本没有发生碰撞。而连续碰撞检测完全不使用时间步长，它创建整个时间步长的扫描体，并查找该扫描体是否与任何物体相交。这既昂贵又不准确（因为只使用简单的圆形碰撞形状，而非完整的碰撞形状）。
用法
连续碰撞检测是按对象设置的，您可以在同一场景中同时使用使用ccd和不使用ccd的对象。如下所示，在物理对象上设置ccd：
RigidBodyControl physicsObject = new RigidBodyControl(mass);
physicsObject.setCcdMotionThreshold(expectedWidthOfThinObject);
physicsObject.setCcdSweptSphereRadius(radiusOfSphereThatWillFullyContainObject);
完整示例
以下源代码将展示使用连续碰撞检测和使用标准碰撞检测之间的差异。它会发射两组球，一组快速，一组慢速，并在5秒的时间间隔内开启和关闭ccd。慢速球总是与纸张碰撞，只有当ccd开启时，快速球才会碰撞。
import com.jme3.app.SimpleApplication;
import com.jme3.bullet.BulletAppState;
import com.jme3.bullet.control.RigidBodyControl;
import com.jme3.font.BitmapText;
import com.jme3.material.Material;
import com.jme3.math.ColorRGBA;
import com.jme3.math.Vector3f;
import com.jme3.scene.Geometry;
import com.jme3.scene.shape.Box;
import com.jme3.scene.shape.Sphere;
public class BulletTest extends SimpleApplication {
public static void main(String args[]) {
BulletTest app = new BulletTest();
app.start();
}
/** Prepare the Physics Application State (jBullet) */
private BulletAppState bulletAppState;
/** Prepare Materials */
Material wall_mat;
Material slow_mat;
Material fast_mat;
Material floor_mat;
private RigidBodyControl brick_phy;
private static final Box box;
private static final Sphere sphere;
private RigidBodyControl floor_phy;
private static final Box floor;
/** dimensions used for wall */
private static final float brickLength = 2f;
private static final float brickWidth = 0.015f;
private static final float brickHeight = 1f;
static {
/** Initialize the cannon ball geometry */
sphere = new Sphere(32, 32, 0.1f, true, false);
/** Initialize the brick geometry */
box = new Box(brickWidth, brickHeight, brickLength);
/** Initialize the floor geometry */
floor = new Box(10f, 0.1f, 5f);
}
@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);
/** Initialize the scene, materials, and physics space */
initMaterials();
initWall();
initFloor();
setUpHUDText();
}
public static final float FIREPERIOD=0.5f;
double fireTimer=0;
public static final float SWEEPPERIOD=5f;
double sweepTimer=0;
boolean continuouslySweeping=true;
@Override
public void simpleUpdate(float tpf) {
fireTimer+=tpf;
sweepTimer+=tpf;
if (sweepTimer>SWEEPPERIOD){
sweepTimer=0;
continuouslySweeping=!continuouslySweeping;
}
hudText.setText("ContinouslySweeping=" + continuouslySweeping + "(" + (int)(SWEEPPERIOD-sweepTimer) + ")" );
if (fireTimer>FIREPERIOD){
fireTimer=0;
makeCannonBall(new Vector3f(-4,3,0),new Vector3f(6,4,0),slow_mat,continuouslySweeping); //slow arcing ball
makeCannonBall(new Vector3f(-4,3,-0.5f),new Vector3f(10,1,0),fast_mat,continuouslySweeping); //fast straight ball
}
}
public BitmapText hudText;
private void setUpHUDText(){
hudText = new BitmapText(guiFont, false);
hudText.setSize(guiFont.getCharSet().getRenderedSize()); // font size
hudText.setColor(ColorRGBA.White); // font color
hudText.setText("ContinouslySweeping=true"); // the text
hudText.setLocalTranslation(300, hudText.getLineHeight(), 0); // position
guiNode.attachChild(hudText);
}
/** Initialize the materials used in this scene. */
public void initMaterials() {
wall_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
wall_mat.setColor("Color", ColorRGBA.Blue);
fast_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
fast_mat.setColor("Color", ColorRGBA.Red);
slow_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
slow_mat.setColor("Color", ColorRGBA.Green);
floor_mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
floor_mat.setColor("Color", ColorRGBA.Gray);
}
/** 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);
/* Make the floor physical with mass 0.0f! */
floor_phy = new RigidBodyControl(0.0f);
floor_geo.addControl(floor_phy);
bulletAppState.getPhysicsSpace().add(floor_phy);
}
/** This loop builds a wall out of individual bricks. */
public void initWall() {
Vector3f location=new Vector3f(2,2,0);
Geometry brick_geo = new Geometry("brick", box);
brick_geo.setMaterial(wall_mat);
rootNode.attachChild(brick_geo);
/** Position the brick geometry */
brick_geo.setLocalTranslation(location);
//paper thin objects will fall down, mass 0 clamps it in position
brick_phy = new RigidBodyControl(0);
/** Add physical brick to physics space. */
brick_geo.addControl(brick_phy);
bulletAppState.getPhysicsSpace().add(brick_phy);
}
public void makeCannonBall(Vector3f startPoint, Vector3f initialVelocity, Material material, boolean continuouslySwept) {
/** Create a cannon ball geometry and attach to scene graph. */
Geometry ball_geo = new Geometry("cannon ball", sphere);
ball_geo.setMaterial(material);
rootNode.attachChild(ball_geo);
/** Position the cannon ball */
ball_geo.setLocalTranslation(startPoint);
/** Make the ball physcial with a mass > 0.0f */
RigidBodyControl 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(initialVelocity);
if (continuouslySwept){
ball_phy.setCcdMotionThreshold(0.015f);
ball_phy.setCcdSweptSphereRadius(0.01f);
}
}
}
通过对两组球的连续检测（从左上方进入的球），可以发现球弹跳效果正常：
关闭连续检测后，快速运动的球（红色）会像穿过空气一样穿过纸张（偶尔也有慢速球（绿色）这样做）：
注：此代码是基于Hello Physics代码并结合高级物理学中的功能进行修改的。