/*******************************************************************************
*
* McStas, neutron ray-tracing package
*         Copyright 1997-2002, All rights reserved
*         Risoe National Laboratory, Roskilde, Denmark
*         Institut Laue Langevin, Grenoble, France
*
* Component: Pi_2_rotator
*
* %IDENTIFICATION
* Written by: Erik Knudsen (erkn@fysik.dtu.dk)
* Date: 8/4-2008
* Origin: Risoe
*
* Ideal π/2-rotator
*
* %Description
* Simple, idelized, component that turns the polarization exactly π/2 around the specified vector
* vector (rx,ry,rx).
* The geometry of the component is realized as a box, where the the spin is rotated at the z-midpoint.
*
* %PARAMETERS
* xwidth: [m]   width of the component 
* yheight: [m]  height of the component 
* zdepth: [m]   thickness of the component 
* rx: []        x-component of the rotation axis
* ry: []        y-component of the rotation axis
* rz: []        z-component of the rotation axis
*
* %LINKS
*
* %END
****************************************************************************/

DEFINE COMPONENT Pol_pi_2_rotator

SETTING PARAMETERS(xwidth=0.1, yheight=0.1, zdepth=0.01, rx=0,ry=0,rz=1)


SHARE
%{
%}

DECLARE
%{
%}

INITIALIZE
%{
  double rr = scalar_prod (rx, ry, rz, rx, ry, rz);
  if (rr != 1) {
    rx = rx / sqrt (rr);
    ry = ry / sqrt (rr);
    rz = rz / sqrt (rr);
  }
%}

TRACE
%{
  double t1, t2 = 0;
  double rxs_x, rxs_y, rxs_z, rdots;
  /*check to see if we actually hit the component*/
  if (!box_intersect (&t1, &t2, x, y, z, vx, vy, vz, xwidth, yheight, zdepth)) {
    ABSORB;
  }

  /*if so, propagate to the halfway point - i.e. the z-center fo the turner*/
  PROP_DT ((t2 - t1) / 2.0);
  /*now turn spin and set SCATTERED, This to get a reference pt in mcdisplay*/

  /*rodrigues' formula gives a rotation of v around u as: v_rot=cos(phi)v + sin(phi) u x v +(1-cos(phi)) (u.v)u*/
  rdots = scalar_prod (rx, ry, rz, sx, sy, sz);
  vec_prod (rxs_x, rxs_y, rxs_z, rx, ry, rz, sx, sy, sz);
  sx = rxs_x + rdots * rx;
  sy = rxs_y + rdots * ry;
  sz = rxs_z + rdots * rz;

  SCATTERED;
%}

MCDISPLAY
%{
  box ((double)0.0, (double)0.0, (double)0.0, (double)xwidth, (double)yheight, (double)zdepth, 0, 0, 1, 0);
%}
END