Projectile Collision Detection

Engines, Libraries and Tools Java 3D
#1

I have the following code:

            Transform3D localToVWorld = new Transform3D();
            this.getTransform(localToVWorld);  //was getlocalToVWorld();
            bounds = box.getBounds();
            bounds.transform(localToVWorld);

where box is an object that extneds Shape3D and has 24 vertices. It has a BoundingBox shell as well.
then later…

         public boolean hasCollided(GameObject obj) {
            if(bounds.intersect(obj.getShell())) {
                  return true;
            }
            else {
                  return false;
            }
            
      }

where getShell() rerturns the box’s boundingbox.
This code seems to work 50/50. If an opponent moves x distance away, every shot may collide, then another x distance and all shots pass right thru. Rotate 3 degrees and voila, hits again, rotate a littler further and pass thru. AM I not properly updated the boundingbox location? This is true detection and not avoidance.
Thanks

#2

bounds = box.getBounds();
bounds.transform(localToVWorld);

I think that you are stepping on xith3d toes here, by modifying it’s internal bounds. You should create your own copy of bounds and then play with it.

#3

actually it is my own, pure java3d, no xith. I create my opwn bounds, then transform it, then apply it to the actual object shape3d.

#4

From what I see here I cannot guess what might be wrong.

Generally working with bound requires some in-depth thinking. Normally the local bounds of an object it static, so I wonder what you mean by [quote]I create my opwn bounds, then transform it, then apply it to the actual object shape3d.
[/quote]
What kind of bounds does getShell() return? Global, local? With ‘this.getLocalToVWorld()’ … who is ‘this’? And where is it located in the scenegraph with respect to the bounds that is transformed?

#5

My apologies, did kinda skimp on the code details…here is the class:

package server;

import javax.media.j3d.*;
import javax.vecmath.*;

public abstract class GameObject extends TransformGroup {

      float x,y,z;
      double rotation;
      int objID;

      private double adjust = 2.356194490192345;

      private double moveRate = 0.2;
        private double speed = 0.7;

      Transform3D tf;
      Vector3f loc;
      Transform3D rotator;
      Matrix3d m;
      Box box;
      Bounds bounds;
      BranchGroup parent = null;
      boolean parentIsSet = false;
      CollisionDetector cd;
      BoundingSphere cBounds;

      public static ServerUniverseManager universe;

      GameObject(int id, float xx, float yy, float zz, double rot, Box b, int type) {
            objID = id;
            x = xx;
            y = yy;
            z = zz;
            rotation = rot;
            box = b;
            box.setCapability(Shape3D.ALLOW_GEOMETRY_READ);

            this.setCapability(TransformGroup.ALLOW_TRANSFORM_READ);
            this.setCapability(TransformGroup.ALLOW_TRANSFORM_WRITE);
            this.setCapability(Node.ALLOW_LOCAL_TO_VWORLD_READ);
            this.addChild(box);
            bounds = box.getBounds();
            //cd = new CollisionDetector(this);
            //cBounds = new BoundingSphere(new Point3d(0.0,0.0,0.0), Double.POSITIVE_INFINITY);
            //cd.setSchedulingBounds(cBounds);

            tf = new Transform3D();
            loc = new Vector3f();
            rotator = new Transform3D();
            m = new Matrix3d();
            universe.addGameObject(this, type);
            //universe.addWorldObject(cd);
            if(this.isLive()) {
                  setLocation(x,y,z,rotation);
            }

      }

      public static void setUniverse(ServerUniverseManager u) {
            universe = u;
      }

      protected void setParent(BranchGroup bg) {
            parent = bg;
            parentIsSet = true;
      }

      protected boolean hasParent() {
            return parentIsSet;
      }

      protected boolean removeMe(int type) {
            if(hasParent()) {
                  parent.detach();
                  System.out.println("detached from parent on server...");
                  universe.removeGameObject(this, type);
                  return true;
            }
            return false;
      }

      protected boolean removeMe(int type, String msg) {
                  if(hasParent()) {
                        parent.detach();
                        System.out.println(msg);
                        universe.removeGameObject(this, type);
                        return true;
                  }
                  return false;
      }

      protected int getObjID() {
            return objID;
      }

      protected boolean match(int id) {
            return id == objID;
      }

      //public TransformGroup getTG() {
      //      return group;
      //}
      public Shape3D getShape() {
            return box;
      }

      public Bounds getShell() {
            return bounds;
      }

      public void setLocation(float x, float y, float z, double rot) {
            rotation = rot;
            rotator.rotY(rot);
            tf.setTranslation(new Vector3f(x,y,z));
            // now rotate the transform
            tf.mul(rotator);
            // aplly to transform group so shape3d is moved for collision detection
            this.setTransform(tf);
            //set new location into Vector3f and Matrix3d
            tf.get(loc);
            tf.get(m);
            //now set the transform to the bounding box
            //getShell().transform(tf);
            Transform3D localToVWorld = new Transform3D();
            this.getTransform(localToVWorld);  //was getlocalToVWorld();
            bounds = box.getBounds();
            bounds.transform(localToVWorld);
            getShell().set(bounds);
            //System.out.println(getShell().toString());
      }

      public float getX() {
            return loc.x;
      }

      public float getY() {
            return loc.y;
      }

      public float getZ() {
            return loc.z;
      }

      public double getRot() {
            //return (double)Math.atan2 (m.m22 - m.m02, m.m20 - m.m00) - adjust;
            return rotation;
      }

      public void doMove(Vector3d theMove) {
            Transform3D toMove = new Transform3D();
            toMove.setTranslation(theMove);
            tf.mul(toMove);
            this.setTransform(tf);
            tf.get(loc);
            tf.get(m);
            //now set the transform to the bounding box
            //getShell().transform(tf);
            Transform3D localToVWorld = new Transform3D();
            this.getTransform(localToVWorld);  //was getlocalToVWorld();
            bounds = box.getBounds();
            bounds.transform(localToVWorld);
            getShell().set(bounds);
            //System.out.println(bounds.toString());
      }

        protected void moveForward()
        {
          doMove(new Vector3d(0.0,0.0, -getMovementRate()));
        }

         protected double getMovementRate()
    {
       return moveRate * speed;
        }

         public void setMovementRate(double meters)
         {
           moveRate = meters; // Travel rate in meters/frame
         }

      public CollisionDetector getCollider() {
            return cd;
      }

         // collision detection???
         public boolean hasCollided(GameObject obj) {
            if(bounds.intersect(obj.getShell())) {
                  return true;
            }
            else {
                  return false;
            }
            //System.out.println("This: " + getX() + " other: " + obj.getX());
            //if(getX() == obj.getX() && getZ() == obj.getZ())
            //      return true;
            //return false;
      }


//eof
}

The code from my first post is call the above class to get the bounds.

Again, Box is a Shape3d that I do this in:

      BoundingPolytope poly = null;
      BoundingBox shell = null;
      shell = new BoundingBox(verts[0], verts[7]); // was 4  16
      poly = new BoundingPolytope(shell);
      setBounds(poly);

from 24 verts of a quadarray.

#6

Did you try slowing down your bullets? Perhaps they move too fast and pass through other objects without collision.

#7

That is not an issue with java3d cause it can detect collisions by expanding a cylinder from the players pos to the new pos. So whatever the speed it takes, if that cylinder collides with anything then its not a free movement.

#8

When talking generally about a different approach, I suggest using the pick utility. Thats the way the FlyingGuns machinegun works.

#9

so you run a short pick ray in front of the projectile?

#10

Yes and no … FlyingGuns bullets are of an ‘immediate hit’ type (highly valuable in network handling!). So I have a long pick ray starting at the weapon.

In any case the pick rays should be longer than the distance a bullet can make during one frame :slight_smile:

#11

long pick ray = if ray crosses target, its a hit?

Projectile should have a ray that is 1 meter long if you move half meter per frame…

#12

[quote]long pick ray = if ray crosses target, its a hit?
[/quote]
Yes. Very easy.

… if the projectile moves half a meter…