[SOLVED] Jme3 Beginner: Understanding the rotation Concept

Troubleshooting General Help
1

so if u have a spatial created at (0,0,0) if you rotate 180 degrees around the y axis using something like

spatial.rotate(0,3.14,0) the spatial turns around in 180 degrees.

Now if that spatial is created at (5,0,0) , and using the same rotation function it will rotate around the same y axis in a circular motion around it. How do I go about making the spatial rotate around itself (i.e. staying at the same location but rotating in 180 degrees like its located at 0,0,0 )?

2

You could translate the box to the origin, perform the rotation and translate back to it’s position.



Or you could have a node attached to the origin (center) of the box and perform the rotation.

3

Tried both no luck… can’t tell what i’m doing wrong. I do prefer the 2nd option tho



so now working on the rotation translation and l would do something like:



[java]spatial.setLocalTranslation(5,0,0);

spatial.rotate(0,(float) 1.1,0);

spatial.setLocalTranslation(-5,0,0); [/java]



won’t do it , still rotates in a circular way, what am I doing wrong?

4

Can you post the rest of the code you’re working with? I think something else is getting fudged up… I’m actually getting the rotation around the origin of the cube without extra translation or having to attach an extra node.

Here’s what I have based off of simpleapplication:



NOTE: Even using your method of rotation, I get a rotation about the origin of the box

[java]package mygame;

import com.jme3.app.SimpleApplication;

import com.jme3.material.Material;

import com.jme3.math.ColorRGBA;

import com.jme3.math.FastMath;

import com.jme3.math.Matrix3f;

import com.jme3.math.Vector3f;

import com.jme3.math.Quaternion;

import com.jme3.renderer.RenderManager;

import com.jme3.scene.Geometry;

import com.jme3.scene.shape.Box;

/**

  • test
  • @author normenhansen

    */

    public class Main extends SimpleApplication {

    Box b;

    Geometry geom;

    Material mat;

    public static void main(String[] args) {

    Main app = new Main();

    app.start();

    }

    @Override

    public void simpleInitApp() {

    b = new Box(Vector3f.ZERO, 1, 1, 1);

    geom = new Geometry("Box", b);

    geom.setLocalTranslation(5,0,0);

    geom.updateModelBound();

    mat = new Material(assetManager, "Common/MatDefs/Misc/SolidColor.j3md");

    mat.setColor("m_Color", ColorRGBA.Blue);

    geom.setMaterial(mat);

    rootNode.attachChild(geom);

    }

    @Override

    public void simpleUpdate(float tpf) {

    //TODO: add update code

    Quaternion quatA = new Quaternion();

    quatA = quatA.fromAngleAxis(FastMath.HALF_PI * tpf, Vector3f.UNIT_Y);

    geom.rotate(quatA);

    }

    }

    [/java]
5

weird…

This is where I create my spatials first spatial model[0] is 0,0,0 and 2nd one model[1] is 5,0,0

[java]

public void create3dObjects(AnimationEvent[] eArray) {

for (int i=0; i<= spatialsNumber - 1; i++)

{

Box d_unit = new Box(new Vector3f(eArray.x, eArray.y, eArray.z), 1, .25f, .5f);

model = new Geometry(eArray.id, d_unit );

if(assetManager == null)

{

System.out.println("WARNING: Asset Manager is null");

}

AssetManager assetManager = null;

assetManager = JmeSystem.newAssetManager(Thread.currentThread().getContextClassLoader().getResource("com/jme3/asset/Desktop.cfg"));

Material mat1 = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");

mat1.setColor("Color", ColorRGBA.Orange);

model.setMaterial(mat1);

rootNode.attachChild(model);

}

}

[/java]

and here is when I am attempting the rotation

[java]

float[] rotation = {0, 3, 0};

cinematic.addCinematicEvent(4, new RotationTrack(model[1], rotation, 1));[/java]

this will rotate aorund the main Y axis (circular and not around itself)

I tried nodes and translation same thing

6

as i said in the other post, create the box at 0,0,0 then translate the geometry.



the thing is new Box(new Vector3f(eArray.x, eArray.y, eArray.z), 1, .25f, .5f); offsets the vertices of the mesh according to the given center, but it’s not the center of the geometry.

I admit this is quite confusing, i never understood why the box constructor takes the “center” as a parameter.

1 Like
7

Great! Thanks