TwistyPuzzleLib

    private boolean mRotAxisIsNormal;

    private final float[] mNormalTouchPoint;

    private float mNormalRotAngle;

      if( !mRotAxisIsNormal )

        {

        float dx = x-mStartRotX;

        float dy = y-mStartRotY;

        float alpha = dx*mAxis[0] + dy*mAxis[1];

        float x2 = dx - alpha*mAxis[0];

        float y2 = dy - alpha*mAxis[1];

        float len = (float)Math.sqrt(x2*x2 + y2*y2);

        // we have the length of 1D vector 'angle', now the direction:

        float tmp = mAxis[1]==0 ? -mAxis[0]*y2 : mAxis[1]*x2;

        float angle = (tmp>0 ? 1:-1)*len*mRotationFactor;

        mCurrentAngle = SWIPING_SENSITIVITY*angle;

        mPreRender.getObject().continueRotation(mCurrentAngle);

        addSpeedProbe(x2,y2);

        }

      else

        {

        float rotAngle = computeNormalRotAngle(mNormalTouchPoint[0]-x,mNormalTouchPoint[1]-y);

        mCurrentAngle = rotAngle - mNormalRotAngle;

        mPreRender.getObject().continueRotation(mCurrentAngle);

        }

      }

///////////////////////////////////////////////////////////////////////////////////////////////////

    private void correctRotationAxis()

      {

      if( mAxis[0]==0 && mAxis[1]==0 )

        {

        mRotAxisIsNormal = true;

        // 0. get face center in object space

        // 1. multiply it by mQuat

        // 2. multiply if by mObjectRatio. Let the result be (x,y,z)

        // 3. let D be CAMERA_POINT.Z

        // 4. then compute the point on the screen (X,Y) the face center maps to:

        //    (X,Y) = (Ax,Ay) where A = D/(D-z)

        float[] faceCenter = mTouchControl.getTouchedPuzzleCenter();

        float D = CAMERA_POINT.get2();

        float[] rotated = new float[4];

        QuatHelper.rotateVectorByQuat(rotated, faceCenter[0],faceCenter[1],faceCenter[2],faceCenter[3],mQuat);

        TwistyObject object = getObject();

        float ratio = object.getObjectRatio();

        float x = rotated[0] * ratio;

        float y = rotated[1] * ratio;

        float z = rotated[2] * ratio;

        float A = D / (D-z);

        mNormalTouchPoint[0] = A*x;

        mNormalTouchPoint[1] = A*y;

        }

      else

        {

        mRotAxisIsNormal = false;

        }

      }

///////////////////////////////////////////////////////////////////////////////////////////////////

// in degrees

    private float computeNormalRotAngle(float vx, float vy)

      {

      return 0;  // TODO

      correctRotationAxis();

      if( mRotAxisIsNormal ) mNormalRotAngle = computeNormalRotAngle(mNormalTouchPoint[0]-x,mNormalTouchPoint[1]-y);

      mNormalTouchPoint = new float[2];