[SOLVED] WorldTransform rotation issues

[fonta.romain]

Hello !

 

I'm having some trouble using WorldTransform class for a rotation only movement.

 

My code is :

 

/**
* Rotates an object around given axis in the given time
* @param[in] o Object to translate
* @param[in] axis Rotation axis
* @param[in] angle Rotation angle
* @param[in] time Time to travel
*/
void RotateObject(Object o, vec3 axis, float angle, float time)
{
 // Valid time and object ?
 if (o != NULL && time > 0.0f && length(axis) > 0.0f)
 {
  // Declare a world transform
  WorldTransform wtr = node_remove(new WorldTransform()) ;

  // Build a frame in the transform for start point
  int frameId = wtr.addFrame() ;
  wtr.setFrameTransform(frameId, o.getTransform()) ;
  wtr.setFrameTime(frameId, 0) ;

  // Build a new frame for end point
  frameId = wtr.addFrame() ;
  wtr.setFrameTransform(frameId, o.getTransform() * rotate(axis, angle)) ;
  wtr.setFrameTime(frameId, time) ;

  // Add child to this tranform
  wtr.addChild(o) ;

  // And then play !
  wtr.play() ;
 }
}

 

The rotation appears to be done from (0;0;0) coordinates instead of the center of my object.

 

However, this code :

o.setTransform(o.getTransform() * rotate(axis, angle))

produce the correct behavior (rotate around the object's center not depending on its space position).

 

Could you please explain what I'm doing wrong ?

 

Thanks !

[unclebob]

Hi,

 

That is probably because child transformation.

 

Lets put your object transform as T_obj and WorldTransform as T_wt. When you add your object as WorldTransform child it will have T_wt * T_obj world transform.

T_wt in your sample is equal to T_obj * rotate(axis,angle), so child world transform will be T_obj * rotate(axis,angle) * T_obj and that is not what you want.

 

Try to set child transformation to identity matrix. Here I modified your code sample:

 

/**
* Rotates an object around given axis in the given time
* @param[in] o Object to translate
* @param[in] axis Rotation axis
* @param[in] angle Rotation angle
* @param[in] time Time to travel
*/
void RotateObject(Object o, vec3 axis, float angle, float time)
{
 // Valid time and object ?
 if (o != NULL && time > 0.0f && length(axis) > 0.0f)
 {
  // Declare a world transform
  WorldTransform wtr = node_remove(new WorldTransform()) ;

  // Build a frame in the transform for start point
  int frameId = wtr.addFrame() ;
  wtr.setFrameTransform(frameId, o.getTransform()) ;
  wtr.setFrameTime(frameId, 0) ;

  // Build a new frame for end point
  frameId = wtr.addFrame() ;
  wtr.setFrameTransform(frameId, o.getTransform() * rotate(axis, angle)) ;
  wtr.setFrameTime(frameId, time) ;

  // Add child to this tranform
  wtr.addChild(o) ;
  o.setTransform(mat4_identity); // NEW!

  // And then play !
  wtr.play() ;
 }
}

 

Hope this was not complicated. :)

[fonta.romain]

Hello,

 

I understand perfectly :)

 

In fact, it's my models that are not correctly built under 3DS Max and lead to this incorrect behavior to my eyes.

 

 

Thanks for your time !