/*****************/
/* Shading stuff */
/*****************/

#include <libgimp/gimp.h>

#include <gck/gck.h>

#include "mapobject_apply.h"
#include "mapobject_main.h"
#include "mapobject_image.h"
#include "mapobject_shade.h"

gdouble            bx1, by1, bx2, by2;
get_ray_color_func get_ray_color;

typedef struct
{
  gdouble     u, v;
  gdouble     t;
  GimpVector3 s;
  GimpVector3 n;
  gint        face;
} FaceIntersectInfo;

/*****************/
/* Phong shading */
/*****************/

static GckRGB
phong_shade (GimpVector3 *pos,
	     GimpVector3 *viewpoint,
	     GimpVector3 *normal,
	     GimpVector3 *light,
	     GckRGB      *diff_col,
	     GckRGB      *spec_col,
	     gint         type)
{
  GckRGB ambientcolor, diffusecolor, specularcolor;
  gdouble NL, RV, dist;
  GimpVector3 L, NN, V, N;

  /* Compute ambient intensity */
  /* ========================= */

  N = *normal;
  ambientcolor = *diff_col;
  gck_rgb_mul (&ambientcolor, mapvals.material.ambient_int);

  /* Compute (N*L) term of Phong's equation */
  /* ====================================== */

  if (type == POINT_LIGHT)
    gimp_vector3_sub (&L, light, pos);
  else
    L = *light;

  dist = gimp_vector3_length (&L);

  if (dist != 0.0)
    gimp_vector3_mul (&L, 1.0 / dist);

  NL = 2.0 * gimp_vector3_inner_product (&N, &L);

  if (NL >= 0.0)
    {
      /* Compute (R*V)^alpha term of Phong's equation */
      /* ============================================ */

      gimp_vector3_sub (&V, viewpoint, pos);
      gimp_vector3_normalize (&V);

      gimp_vector3_mul (&N, NL);
      gimp_vector3_sub (&NN, &N, &L);
      RV = gimp_vector3_inner_product (&NN, &V);
      RV = pow (RV, mapvals.material.highlight);

      /* Compute diffuse and specular intensity contribution */
      /* =================================================== */

      diffusecolor = *diff_col;
      gck_rgb_mul (&diffusecolor, mapvals.material.diffuse_ref);
      gck_rgb_mul (&diffusecolor, NL);

      specularcolor = *spec_col;
      gck_rgb_mul (&specularcolor, mapvals.material.specular_ref);
      gck_rgb_mul (&specularcolor, RV);

      gck_rgb_add (&diffusecolor, &specularcolor);
      gck_rgb_mul (&diffusecolor, mapvals.material.diffuse_int);
      gck_rgb_clamp (&diffusecolor);

      gck_rgb_add (&ambientcolor, &diffusecolor);
    }

  return ambientcolor;
}

static gint
plane_intersect (GimpVector3 *dir,
		 GimpVector3 *viewp,
		 GimpVector3 *ipos,
		 gdouble     *u,
		 gdouble     *v)
{
  static gdouble det, det1, det2, det3, t;

  imat[0][0] = dir->x;
  imat[1][0] = dir->y;
  imat[2][0] = dir->z;

  /* Compute determinant of the first 3x3 sub matrix (denominator) */
  /* ============================================================= */

  det = (imat[0][0] * imat[1][1] * imat[2][2] +
	 imat[0][1] * imat[1][2] * imat[2][0] +
	 imat[0][2] * imat[1][0] * imat[2][1] -
	 imat[0][2] * imat[1][1] * imat[2][0] -
	 imat[0][0] * imat[1][2] * imat[2][1] -
	 imat[2][2] * imat[0][1] * imat[1][0]);

  /* If the determinant is non-zero, a intersection point exists */
  /* =========================================================== */

  if (det != 0.0)
    {
      /* Now, lets compute the numerator determinants (wow ;) */
      /* ==================================================== */

      det1 = (imat[0][3] * imat[1][1] * imat[2][2] +
	      imat[0][1] * imat[1][2] * imat[2][3] +
	      imat[0][2] * imat[1][3] * imat[2][1] -
	      imat[0][2] * imat[1][1] * imat[2][3] -
	      imat[1][2] * imat[2][1] * imat[0][3] -
	      imat[2][2] * imat[0][1] * imat[1][3]);
 
      det2 = (imat[0][0] * imat[1][3] * imat[2][2] +
	      imat[0][3] * imat[1][2] * imat[2][0] +
	      imat[0][2] * imat[1][0] * imat[2][3] -
	      imat[0][2] * imat[1][3] * imat[2][0] -
	      imat[1][2] * imat[2][3] * imat[0][0] -
	      imat[2][2] * imat[0][3] * imat[1][0]);
 
      det3 = (imat[0][0] * imat[1][1] * imat[2][3] +
	      imat[0][1] * imat[1][3] * imat[2][0] +
	      imat[0][3] * imat[1][0] * imat[2][1] -
	      imat[0][3] * imat[1][1] * imat[2][0] -
	      imat[1][3] * imat[2][1] * imat[0][0] -
	      imat[2][3] * imat[0][1] * imat[1][0]);

      /* Now we have the simultanous solutions. Lets compute the unknowns */
      /* (skip u&v if t is <0, this means the intersection is behind us)  */
      /* ================================================================ */

      t = det1 / det;

      if (t > 0.0)
        {
          *u = 1.0 + ((det2 / det) - 0.5);
          *v = 1.0 + ((det3 / det) - 0.5);

      	  ipos->x = viewp->x + t * dir->x;
          ipos->y = viewp->y + t * dir->y;
          ipos->z = viewp->z + t * dir->z;

          return TRUE;
        }
    }

  return FALSE;
}

/*****************************************************************************
 * These routines computes the color of the surface
 * of the plane at a given point
 *****************************************************************************/

GckRGB
get_ray_color_plane (GimpVector3 *pos)
{
  GckRGB color = background;
  static gint inside = FALSE;
  static GimpVector3 ray, spos;
  static gdouble vx, vy;

  /* Construct a line from our VP to the point */
  /* ========================================= */

  gimp_vector3_sub (&ray, pos, &mapvals.viewpoint);
  gimp_vector3_normalize (&ray);

  /* Check for intersection. This is a quasi ray-tracer. */
  /* =================================================== */

  if (plane_intersect (&ray, &mapvals.viewpoint, &spos, &vx, &vy) == TRUE)
    {
      color = get_image_color (vx, vy, &inside);

      if (color.a!=0.0 && inside == TRUE &&
	  mapvals.lightsource.type != NO_LIGHT)
        {
          /* Compute shading at this point */
          /* ============================= */

          color = phong_shade (&spos,
			       &mapvals.viewpoint,
			       &mapvals.normal,
			       &mapvals.lightsource.position,
			       &color,
			       &mapvals.lightsource.color,
			       mapvals.lightsource.type);

          gck_rgb_clamp (&color);
        }
    }
  
  if (color.a == 0.0)
    color = background;

  return color;
}

/***********************************************************************/
/* Given the NorthPole, Equator and a third vector (normal) compute    */
/* the conversion from spherical oordinates to image space coordinates */
/***********************************************************************/

static void
sphere_to_image (GimpVector3 *normal,
		 gdouble     *u,
		 gdouble     *v)
{
  static gdouble alpha, fac;
  static GimpVector3 cross_prod;

  alpha = acos (-gimp_vector3_inner_product (&mapvals.secondaxis, normal));

  *v = alpha / G_PI;

  if (*v == 0.0 || *v == 1.0)
    *u = 0.0;
  else
    {
      fac = (gimp_vector3_inner_product (&mapvals.firstaxis, normal) /
	     sin (alpha));

      /* Make sure that we map to -1.0..1.0 (take care of rounding errors) */
      /* ================================================================= */

      fac = CLAMP (fac, -1.0, 1.0);

      *u = acos (fac) / (2.0 * G_PI);

      cross_prod = gimp_vector3_cross_product (&mapvals.secondaxis,
					       &mapvals.firstaxis);

      if (gimp_vector3_inner_product (&cross_prod, normal) < 0.0)
        *u = 1.0 - *u;
    }
}

/***************************************************/
/* Compute intersection point with sphere (if any) */
/***************************************************/

static gint
sphere_intersect (GimpVector3 *dir,
		  GimpVector3 *viewp,
		  GimpVector3 *spos1,
		  GimpVector3 *spos2)
{
  static gdouble alpha, beta, tau, s1, s2, tmp;
  static GimpVector3 t;

  gimp_vector3_sub (&t, &mapvals.position, viewp);

  alpha = gimp_vector3_inner_product (dir, &t);
  beta  = gimp_vector3_inner_product (&t, &t);

  tau = alpha * alpha - beta + mapvals.radius * mapvals.radius;

  if (tau >= 0.0)
    {
      tau = sqrt (tau);
      s1 = alpha + tau;
      s2 = alpha - tau;

      if (s2 < s1)
        {
          tmp = s1;
          s1 = s2;
          s2 = tmp;
        }

      spos1->x = viewp->x + s1 * dir->x;
      spos1->y = viewp->y + s1 * dir->y;
      spos1->z = viewp->z + s1 * dir->z;
      spos2->x = viewp->x + s2 * dir->x;
      spos2->y = viewp->y + s2 * dir->y;
      spos2->z = viewp->z + s2 * dir->z;

      return TRUE ;
    }

  return FALSE;
}

/*****************************************************************************
 * These routines computes the color of the surface
 * of the sphere at a given point
 *****************************************************************************/

GckRGB
get_ray_color_sphere (GimpVector3 *pos)
{
  GckRGB color=background;
  static GckRGB color2;
  static gint inside=FALSE;
  static GimpVector3 normal,ray,spos1,spos2;
  static gdouble vx,vy;

  /* Check if ray is within the bounding box */
  /* ======================================= */
  
  if (pos->x<bx1 || pos->x>bx2 || pos->y<by1 || pos->y>by2)
    return(color);

  /* Construct a line from our VP to the point */
  /* ========================================= */

  gimp_vector3_sub (&ray, pos, &mapvals.viewpoint);
  gimp_vector3_normalize (&ray);

  /* Check for intersection. This is a quasi ray-tracer. */
  /* =================================================== */

  if (sphere_intersect (&ray, &mapvals.viewpoint, &spos1, &spos2) == TRUE)
    {
      /* Compute spherical to rectangular mapping */
      /* ======================================== */

      gimp_vector3_sub (&normal, &spos1, &mapvals.position);
      gimp_vector3_normalize (&normal);
      sphere_to_image (&normal, &vx, &vy);
      color=get_image_color (vx, vy, &inside);

      /* Check for total transparency... */
      /* =============================== */

      if (color.a < 1.0)
        {
          /* Hey, we can see  through here!      */
          /* Lets see what's on the other side.. */
          /* =================================== */

          color = phong_shade (&spos1,
			       &mapvals.viewpoint,
			       &normal,
			       &mapvals.lightsource.position,
			       &color,
			       &mapvals.lightsource.color,
			       mapvals.lightsource.type);

          gck_rgba_clamp (&color);

          gimp_vector3_sub (&normal, &spos2, &mapvals.position);
          gimp_vector3_normalize (&normal);
          sphere_to_image (&normal, &vx, &vy); 
          color2 = get_image_color (vx, vy, &inside);

          /* Make the normal point inwards */
          /* ============================= */

          gimp_vector3_mul (&normal, -1.0);

          color2=phong_shade (&spos2,
			      &mapvals.viewpoint,
			      &normal,
			      &mapvals.lightsource.position,
			      &color2,
			      &mapvals.lightsource.color,
			      mapvals.lightsource.type);

          gck_rgba_clamp (&color2);

          if (mapvals.transparent_background == FALSE && color2.a < 1.0)
            {
              color2.r = (color2.r*color2.a)+(background.r*(1.0-color2.a));
              color2.g = (color2.g*color2.a)+(background.g*(1.0-color2.a));
              color2.b = (color2.b*color2.a)+(background.b*(1.0-color2.a));
              color2.a = 1.0;
            }

          /* Compute a mix of the first and second colors */
          /* ============================================ */

          color.r = color.r*color.a+(1.0-color.a)*color2.r;
          color.g = color.g*color.a+(1.0-color.a)*color2.g;
          color.b = color.b*color.a+(1.0-color.a)*color2.b; 
          color.a = color.a+color2.a;

          gck_rgba_clamp (&color);
        }
      else if (color.a!=0.0 &&
	       inside==TRUE &&
	       mapvals.lightsource.type!=NO_LIGHT)
        {
          /* Compute shading at this point */
          /* ============================= */

          color = phong_shade (&spos1,
			       &mapvals.viewpoint,
			       &normal,
			       &mapvals.lightsource.position,
			       &color,
			       &mapvals.lightsource.color,
			       mapvals.lightsource.type);

          gck_rgba_clamp (&color);
        }
    }
  
  if (color.a == 0.0)
    color = background;
  
  return color;
}

/***************************************************/
/* Transform the corners of the bounding box to 2D */
/***************************************************/

void
compute_bounding_box (void)
{
  GimpVector3 p1,p2;
  gdouble t;
  GimpVector3 dir;

  p1=mapvals.position;
  p1.x-=(mapvals.radius+0.01);
  p1.y-=(mapvals.radius+0.01);

  p2=mapvals.position;
  p2.x+=(mapvals.radius+0.01);
  p2.y+=(mapvals.radius+0.01);

  gimp_vector3_sub (&dir, &p1, &mapvals.viewpoint);
  gimp_vector3_normalize (&dir);

  if (dir.z!=0.0)
    {
      t=(-1.0*mapvals.viewpoint.z)/dir.z;
      p1.x=(mapvals.viewpoint.x+t*dir.x);
      p1.y=(mapvals.viewpoint.y+t*dir.y);
    }

  gimp_vector3_sub (&dir, &p2, &mapvals.viewpoint);
  gimp_vector3_normalize (&dir);

  if (dir.z!=0.0)
    {
      t=(-1.0*mapvals.viewpoint.z)/dir.z;
      p2.x=(mapvals.viewpoint.x+t*dir.x);
      p2.y=(mapvals.viewpoint.y+t*dir.y);
    }

  bx1=p1.x;
  by1=p1.y;
  bx2=p2.x;
  by2=p2.y;
}

/* These two were taken from the Mesa source. Mesa is written   */
/* and is (C) by Brian Paul. vecmulmat() performs a post-mul by */
/* a 4x4 matrix to a 1x4(3) vector. rotmat() creates a matrix   */
/* that by post-mul will rotate a 1x4(3) vector the given angle */
/* about the given axis.                                        */
/* ============================================================ */

void
vecmulmat (GimpVector3 *u,
	   GimpVector3 *v,
	   gfloat       m[16])
{
   gfloat v0=v->x, v1=v->y, v2=v->z;
#define M(row,col)  m[col*4+row]
   u->x = v0 * M(0,0) + v1 * M(1,0) + v2 * M(2,0) + M(3,0);
   u->y = v0 * M(0,1) + v1 * M(1,1) + v2 * M(2,1) + M(3,1);
   u->z = v0 * M(0,2) + v1 * M(1,2) + v2 * M(2,2) + M(3,2);
#undef M
}

void
rotatemat (gfloat       angle,
	   GimpVector3 *v,
	   gfloat       m[16])
{
   /* This function contributed by Erich Boleyn (erich@uruk.org) */
   gfloat mag, s, c;
   gfloat xx, yy, zz, xy, yz, zx, xs, ys, zs, one_c;
   gfloat IdentityMat[16];
   gint cnt;

   s = sin( angle * (G_PI / 180.0) );
   c = cos( angle * (G_PI / 180.0) );

   mag = sqrt( v->x*v->x + v->y*v->y + v->z*v->z );

   if (mag == 0.0) {
      /* generate an identity matrix and return */

      for (cnt=0;cnt<16;cnt++)
        IdentityMat[cnt]=0.0;
    
      IdentityMat[0] = 1.0;
      IdentityMat[5] = 1.0;
      IdentityMat[10] = 1.0;
      IdentityMat[15] = 1.0;

      memcpy(m, IdentityMat, sizeof(gfloat)*16);
      return;
   }

   v->x /= mag;
   v->y /= mag;
   v->z /= mag;

#define M(row,col)  m[col*4+row]

   xx = v->x * v->x;
   yy = v->y * v->y;
   zz = v->z * v->z;
   xy = v->x * v->y;
   yz = v->y * v->z;
   zx = v->z * v->x;
   xs = v->x * s;
   ys = v->y * s;
   zs = v->z * s;
   one_c = 1.0F - c;

   M(0,0) = (one_c * xx) + c;
   M(0,1) = (one_c * xy) - zs;
   M(0,2) = (one_c * zx) + ys;
   M(0,3) = 0.0F;

   M(1,0) = (one_c * xy) + zs;
   M(1,1) = (one_c * yy) + c;
   M(1,2) = (one_c * yz) - xs;
   M(1,3) = 0.0F;

   M(2,0) = (one_c * zx) - ys;
   M(2,1) = (one_c * yz) + xs;
   M(2,2) = (one_c * zz) + c;
   M(2,3) = 0.0F;

   M(3,0) = 0.0F;
   M(3,1) = 0.0F;
   M(3,2) = 0.0F;
   M(3,3) = 1.0F;

#undef M
}

/* Transpose the matrix m. If m is orthogonal (like a rotation matrix), */
/* this is equal to the inverse of the matrix.                          */
/* ==================================================================== */

void
transpose_mat (gfloat m[16])
{
  gint i,j;
  gfloat t;

  for (i=0;i<4;i++)
    {
      for (j=0;j<i;j++)
        {
          t = m[j*4+i];
          m[j*4+i] = m[i*4+j];
          m[i*4+j] = t;
        }
    }
}

/* Compute the matrix product c=a*b */
/* ================================ */

void
matmul (gfloat a[16],
	gfloat b[16],
	gfloat c[16])
{
  gint   i,j,k;
  gfloat value;
  
#define A(row,col)  a[col*4+row]
#define B(row,col)  b[col*4+row]
#define C(row,col)  c[col*4+row]

  for (i=0;i<4;i++)
    {
      for (j=0;j<4;j++)
        {
	  value = 0.0;
	  for (k=0;k<4;k++)
	    value += A(i,k)*B(k,j);
          
          C(i,j) = value;
        }
    }

#undef A
#undef B
#undef C
}

void
ident_mat (gfloat m[16])
{
  gint   i,j;
  
#define M(row,col)  m[col*4+row]
  
  for (i=0;i<4;i++)
    {
      for (j=0;j<4;j++)
        {
          if (i==j)
            M(i,j) = 1.0;
          else
            M(i,j) = 0.0;
        }
    }  

#undef M
}

static gboolean
intersect_rect (gdouble            u,
		gdouble            v,
		gdouble            w,
		GimpVector3        viewp,
		GimpVector3        dir,
		FaceIntersectInfo *face_info)
{
  gboolean result = FALSE;
  gdouble u2,v2;
  
  if (dir.z!=0.0)
    {
      u2 = u / 2.0;
      v2 = v / 2.0;

      face_info->t = (w-viewp.z)/dir.z;
      face_info->s.x = viewp.x + face_info->t*dir.x;
      face_info->s.y = viewp.y + face_info->t*dir.y;
      face_info->s.z = w;

      if (face_info->s.x>=-u2 && face_info->s.x<=u2 && 
          face_info->s.y>=-v2 && face_info->s.y<=v2)
        {
          face_info->u = (face_info->s.x + u2)/u;
          face_info->v = (face_info->s.y + v2)/v;
          result = TRUE;
        }
    }
  
  return(result);
}

static gboolean
intersect_box (GimpVector3        scale,
	       GimpVector3        viewp,
	       GimpVector3        dir,
	       FaceIntersectInfo *face_intersect)
{
  GimpVector3 v,d,tmp,axis[3];
  FaceIntersectInfo face_tmp;
  gboolean result = FALSE;
  gfloat m[16];
  gint i = 0;

  gimp_vector3_set(&axis[0], 1.0,0.0,0.0);
  gimp_vector3_set(&axis[1], 0.0,1.0,0.0);
  gimp_vector3_set(&axis[2], 0.0,0.0,1.0);

  /* Front side */
  /* ========== */

  if (intersect_rect(scale.x,scale.y,scale.z/2.0,viewp,dir,&face_intersect[i])==TRUE)
    {
      face_intersect[i].face = 0;
      gimp_vector3_set(&face_intersect[i++].n, 0.0,0.0,1.0);
      result = TRUE;
    }

  /* Back side */
  /* ========= */

  if (intersect_rect(scale.x,scale.y,-scale.z/2.0,viewp,dir,&face_intersect[i])==TRUE)
    {
      face_intersect[i].face = 1;
      face_intersect[i].u = 1.0 - face_intersect[i].u;
      gimp_vector3_set(&face_intersect[i++].n, 0.0,0.0,-1.0);
      result = TRUE;
    }

  /* Check if we've found the two possible intersection points */
  /* ========================================================= */
  
  if (i<2)
    {
      /* Top: Rotate viewpoint and direction into rectangle's local coordinate system */
      /* ============================================================================ */
  
      rotatemat(90, &axis[0], m);
      vecmulmat(&v,&viewp,m);
      vecmulmat(&d,&dir,m);
    
      if (intersect_rect(scale.x,scale.z,scale.y/2.0,v,d,&face_intersect[i])==TRUE)
        {
          face_intersect[i].face = 2;

          transpose_mat(m);
          vecmulmat(&tmp, &face_intersect[i].s, m);
          face_intersect[i].s = tmp;
          
          gimp_vector3_set(&face_intersect[i++].n, 0.0,-1.0,0.0);
          result = TRUE;
        } 
    }

  /* Check if we've found the two possible intersection points */
  /* ========================================================= */
  
  if (i<2)
    {
      /* Bottom: Rotate viewpoint and direction into rectangle's local coordinate system */
      /* =============================================================================== */
    
      rotatemat(90, &axis[0], m);  
      vecmulmat(&v,&viewp,m);
      vecmulmat(&d,&dir,m);
    
      if (intersect_rect(scale.x,scale.z,-scale.y/2.0,v,d,&face_intersect[i])==TRUE)
        {
          face_intersect[i].face = 3;

          transpose_mat(m);

          vecmulmat(&tmp, &face_intersect[i].s, m);
          face_intersect[i].s = tmp;

          face_intersect[i].v = 1.0 - face_intersect[i].v;

          gimp_vector3_set(&face_intersect[i++].n, 0.0,1.0,0.0);

          result = TRUE;
        }
    }

  /* Check if we've found the two possible intersection points */
  /* ========================================================= */
  
  if (i<2)
    {
      /* Left side: Rotate viewpoint and direction into rectangle's local coordinate system */
      /* ================================================================================== */
    
      rotatemat(90, &axis[1], m);  
      vecmulmat(&v,&viewp,m);
      vecmulmat(&d,&dir,m);

      if (intersect_rect(scale.z,scale.y,scale.x/2.0,v,d,&face_intersect[i])==TRUE)
        {
          face_intersect[i].face = 4;
    
          transpose_mat(m);
          vecmulmat(&tmp, &face_intersect[i].s, m);
          face_intersect[i].s = tmp;

          gimp_vector3_set(&face_intersect[i++].n, 1.0,0.0,0.0);
          result = TRUE;
        }
    }

  /* Check if we've found the two possible intersection points */
  /* ========================================================= */
  
  if (i<2)
    {
      /* Right side: Rotate viewpoint and direction into rectangle's local coordinate system */
      /* =================================================================================== */
  
      rotatemat(90, &axis[1], m);  
      vecmulmat(&v,&viewp,m);
      vecmulmat(&d,&dir,m);
    
      if (intersect_rect(scale.z,scale.y,-scale.x/2.0,v,d,&face_intersect[i])==TRUE)
        {
          face_intersect[i].face = 5;

          transpose_mat(m);
          vecmulmat(&tmp, &face_intersect[i].s, m);

          face_intersect[i].u = 1.0 - face_intersect[i].u;

          gimp_vector3_set(&face_intersect[i++].n, -1.0,0.0,0.0);
          result = TRUE;
        }
    }

  /* Sort intersection points */
  /* ======================== */
  
  if (face_intersect[0].t>face_intersect[1].t)
    {
      face_tmp = face_intersect[0];
      face_intersect[0] = face_intersect[1];
      face_intersect[1] = face_tmp;
    }

  return(result);  
}

GckRGB
get_ray_color_box (GimpVector3 *pos)
{
  GimpVector3 lvp,ldir,vp,p,dir,ns,nn;
  GckRGB color, color2;
  gfloat m[16];
  gint i;
  FaceIntersectInfo face_intersect[2];
  
  color=background;
  vp = mapvals.viewpoint;
  p = *pos;

  /* Translate viewpoint so that the box has its origin */
  /* at its lower left corner.                          */
  /* ================================================== */

  vp.x = vp.x - mapvals.position.x;
  vp.y = vp.y - mapvals.position.y;
  vp.z = vp.z - mapvals.position.z;

  p.x = p.x - mapvals.position.x;
  p.y = p.y - mapvals.position.y;
  p.z = p.z - mapvals.position.z;

  /* Compute direction */
  /* ================= */
  
  gimp_vector3_sub(&dir,&p,&vp);
  gimp_vector3_normalize(&dir);

  /* Compute inverse of rotation matrix and apply it to   */
  /* the viewpoint and direction. This transforms the     */
  /* observer into the local coordinate system of the box */
  /* ==================================================== */

  memcpy(m,rotmat,sizeof(gfloat)*16);
  
  transpose_mat(m);
  
  vecmulmat(&lvp,&vp,m);
  vecmulmat(&ldir,&dir,m);

  /* Ok. Now the observer is in the space where the box is located */
  /* with its lower left corner at the origin and its axis aligned */
  /* to the cartesian basis. Check if the transformed ray hits it. */
  /* ============================================================= */

  face_intersect[0].t = 1000000.0;
  face_intersect[1].t = 1000000.0;
  
  if (intersect_box(mapvals.scale,lvp,ldir,face_intersect)==TRUE)
    {
      /* We've hit the box. Transform the hit points and */
      /* normals back into the world coordinate system   */
      /* =============================================== */
      
      for (i=0;i<2;i++)
        {
          vecmulmat(&ns,&face_intersect[i].s,rotmat);
          vecmulmat(&nn,&face_intersect[i].n,rotmat);

          ns.x = ns.x + mapvals.position.x;
          ns.y = ns.y + mapvals.position.y;
          ns.z = ns.z + mapvals.position.z;
          
          face_intersect[i].s = ns;
          face_intersect[i].n = nn;
        }

      color = get_box_image_color(face_intersect[0].face,
                                  face_intersect[0].u,face_intersect[0].v);

      /* Check for total transparency... */
      /* =============================== */

      if (color.a<1.0)
        {
          /* Hey, we can see  through here!      */
          /* Lets see what's on the other side.. */
          /* =================================== */
          
          color = phong_shade (&face_intersect[0].s,
			       &mapvals.viewpoint,
			       &face_intersect[0].n,
			       &mapvals.lightsource.position,
			       &color,
			       &mapvals.lightsource.color,
			       mapvals.lightsource.type);      
    
          gck_rgba_clamp(&color);

          color2 = get_box_image_color(face_intersect[1].face,
                                       face_intersect[1].u,face_intersect[1].v);

          /* Make the normal point inwards */
          /* ============================= */

          gimp_vector3_mul(&face_intersect[1].n,-1.0);

          color2 = phong_shade (&face_intersect[1].s,
				&mapvals.viewpoint,
				&face_intersect[1].n,
				&mapvals.lightsource.position,
				&color2,
				&mapvals.lightsource.color,
				mapvals.lightsource.type);      

          gck_rgba_clamp(&color2);
          
          if (mapvals.transparent_background==FALSE && color2.a<1.0)
            {
              color2.r = (color2.r*color2.a)+(background.r*(1.0-color2.a));
              color2.g = (color2.g*color2.a)+(background.g*(1.0-color2.a));
              color2.b = (color2.b*color2.a)+(background.b*(1.0-color2.a));
              color2.a = 1.0;
            }

          /* Compute a mix of the first and second colors */
          /* ============================================ */
          
          color.r = color.r*color.a+(1.0-color.a)*color2.r;
          color.g = color.g*color.a+(1.0-color.a)*color2.g;
          color.b = color.b*color.a+(1.0-color.a)*color2.b; 
          color.a = color.a+color2.a;

          gck_rgba_clamp(&color);
        }
      else if (color.a!=0.0 && mapvals.lightsource.type!=NO_LIGHT)
        {
           color = phong_shade (&face_intersect[0].s,
				&mapvals.viewpoint,
				&face_intersect[0].n,
				&mapvals.lightsource.position,
				&color,
				&mapvals.lightsource.color,
				mapvals.lightsource.type);      
    
           gck_rgba_clamp (&color);
        }
    }
  else
    {
      if (mapvals.transparent_background == TRUE)
        color.a = 0.0;
    }

  return color;
}

static gboolean
intersect_circle (GimpVector3        vp,
		  GimpVector3        dir,
		  gdouble            w,
		  FaceIntersectInfo *face_info)
{
  gboolean result = FALSE;
  gdouble r,d;
  
#define sqr(a) a*a

  if (dir.y!=0.0)
    {
      face_info->t = (w-vp.y)/dir.y;
      face_info->s.x = vp.x + face_info->t*dir.x;
      face_info->s.y = w;
      face_info->s.z = vp.z + face_info->t*dir.z;

      r = sqrt(sqr(face_info->s.x) + sqr(face_info->s.z));
      
      if (r<=mapvals.cylinder_radius)
        {
          d = 2.0*mapvals.cylinder_radius;
          face_info->u = (face_info->s.x+mapvals.cylinder_radius)/d;
          face_info->v = (face_info->s.z+mapvals.cylinder_radius)/d;
          result = TRUE;
        }
    }

#undef sqr
  
  return(result);  
}

static gboolean
intersect_cylinder (GimpVector3        vp,
		    GimpVector3        dir,
		    FaceIntersectInfo *face_intersect)
{
  gdouble a,b,c,d,e,f,tmp,l;
  gboolean result = FALSE;
  gint i;

#define sqr(a) a*a
 
  a = sqr(dir.x) + sqr(dir.z);
  b = 2.0*(vp.x*dir.x+vp.z*dir.z);
  c = sqr(vp.x)+sqr(vp.z)-sqr(mapvals.cylinder_radius);

  d = sqr(b)-4.0*a*c;
  if (d>=0.0)
    {
      e = sqrt(d);
      f = 2.0*a;
    
      if (f!=0.0)
        {
          result = TRUE;      
    
          face_intersect[0].t = (-b+e)/f;
          face_intersect[1].t = (-b-e)/f;
    
          if (face_intersect[0].t>face_intersect[1].t)
            {
              tmp = face_intersect[0].t;
              face_intersect[0].t = face_intersect[1].t;
              face_intersect[1].t = tmp;
            }
          
          for (i=0;i<2;i++)
            {
              face_intersect[i].s.x = vp.x + face_intersect[i].t * dir.x;
              face_intersect[i].s.y = vp.y + face_intersect[i].t * dir.y;
              face_intersect[i].s.z = vp.z + face_intersect[i].t * dir.z;

              face_intersect[i].n = face_intersect[i].s;
              face_intersect[i].n.y = 0.0;
              gimp_vector3_normalize(&face_intersect[i].n);

              l = mapvals.cylinder_length/2.0;

              face_intersect[i].u = (atan2(face_intersect[i].s.x,face_intersect[i].s.z)+G_PI)/(2.0*G_PI);
              face_intersect[i].v = (face_intersect[i].s.y+l)/mapvals.cylinder_length;

              /* Mark hitpoint as on the cylinder hull */
              /* ===================================== */
              
              face_intersect[i].face = 0;

              /* Check if we're completely off the cylinder axis */
              /* =============================================== */
    
              if (face_intersect[i].s.y>l || face_intersect[i].s.y<-l)
                {
                  /* Check if we've hit a cap */
                  /* ======================== */
    
                  if (face_intersect[i].s.y>l)
                    {
                      if (intersect_circle(vp,dir,l,&face_intersect[i])==FALSE)
                        result = FALSE;
                      else
                        {
                          face_intersect[i].face = 2;
                          face_intersect[i].v = 1 - face_intersect[i].v;
                          gimp_vector3_set(&face_intersect[i].n, 0.0, 1.0, 0.0);
                        }
                    }
                  else
                    {
                      if (intersect_circle(vp,dir,-l,&face_intersect[i])==FALSE)
                        result = FALSE;
                      else
                        {
                          face_intersect[i].face = 1;
                          gimp_vector3_set(&face_intersect[i].n, 0.0, -1.0, 0.0);
                        }
                    }
                }
            }
        }
    }

#undef sqr
  
  return(result);
}

static GckRGB
get_cylinder_color (gint    face,
		    gdouble u,
		    gdouble v)
{
  GckRGB color;
  gint inside;
  
  if (face==0)
    color = get_image_color(u,v,&inside);
  else
    color = get_cylinder_image_color (face-1,u,v);
  
  return(color);
}

GckRGB
get_ray_color_cylinder (GimpVector3 *pos)
{
  GimpVector3 lvp,ldir,vp,p,dir,ns,nn;
  GckRGB color, color2;
  gfloat m[16];
  gint i;
  FaceIntersectInfo face_intersect[2];
  
  color=background;
  vp = mapvals.viewpoint;
  p = *pos;

  vp.x = vp.x - mapvals.position.x;
  vp.y = vp.y - mapvals.position.y;
  vp.z = vp.z - mapvals.position.z;

  p.x = p.x - mapvals.position.x;
  p.y = p.y - mapvals.position.y;
  p.z = p.z - mapvals.position.z;

  /* Compute direction */
  /* ================= */
  
  gimp_vector3_sub(&dir,&p,&vp);
  gimp_vector3_normalize(&dir);

  /* Compute inverse of rotation matrix and apply it to   */
  /* the viewpoint and direction. This transforms the     */
  /* observer into the local coordinate system of the box */
  /* ==================================================== */

  memcpy(m,rotmat,sizeof(gfloat)*16);
  
  transpose_mat(m);
  
  vecmulmat(&lvp,&vp,m);
  vecmulmat(&ldir,&dir,m);

  if (intersect_cylinder(lvp,ldir,face_intersect)==TRUE)
    {
      /* We've hit the cylinder. Transform the hit points and */
      /* normals back into the world coordinate system        */
      /* ==================================================== */
      
      for (i=0;i<2;i++)
        {
          vecmulmat(&ns,&face_intersect[i].s,rotmat);
          vecmulmat(&nn,&face_intersect[i].n,rotmat);

          ns.x = ns.x + mapvals.position.x;
          ns.y = ns.y + mapvals.position.y;
          ns.z = ns.z + mapvals.position.z;
          
          face_intersect[i].s = ns;
          face_intersect[i].n = nn;
        }

      color = get_cylinder_color(face_intersect[0].face,
                                 face_intersect[0].u,face_intersect[0].v);

      /* Check for total transparency... */
      /* =============================== */

      if (color.a<1.0)
        {
          /* Hey, we can see  through here!      */
          /* Lets see what's on the other side.. */
          /* =================================== */
          
          color = phong_shade (&face_intersect[0].s,
			       &mapvals.viewpoint,
			       &face_intersect[0].n,
			       &mapvals.lightsource.position,
			       &color,
			       &mapvals.lightsource.color,
			       mapvals.lightsource.type);      
    
          gck_rgba_clamp (&color);

          color2 = get_cylinder_color (face_intersect[1].face,
				       face_intersect[1].u,
				       face_intersect[1].v);

          /* Make the normal point inwards */
          /* ============================= */

          gimp_vector3_mul (&face_intersect[1].n, -1.0);

          color2 = phong_shade (&face_intersect[1].s,
				&mapvals.viewpoint,
				&face_intersect[1].n,
				&mapvals.lightsource.position,
				&color2,
				&mapvals.lightsource.color,
				mapvals.lightsource.type);

          gck_rgba_clamp (&color2);
          
          if (mapvals.transparent_background == FALSE && color2.a < 1.0)
            {
              color2.r = (color2.r*color2.a) + (background.r*(1.0-color2.a));
              color2.g = (color2.g*color2.a) + (background.g*(1.0-color2.a));
              color2.b = (color2.b*color2.a) + (background.b*(1.0-color2.a));
              color2.a = 1.0;
            }

          /* Compute a mix of the first and second colors */
          /* ============================================ */
          
          color.r = color.r*color.a + (1.0-color.a)*color2.r;
          color.g = color.g*color.a + (1.0-color.a)*color2.g;
          color.b = color.b*color.a + (1.0-color.a)*color2.b; 
          color.a = color.a+color2.a;

          gck_rgba_clamp (&color);
        }
      else if (color.a != 0.0 && mapvals.lightsource.type != NO_LIGHT)
        {
           color = phong_shade (&face_intersect[0].s,
				&mapvals.viewpoint,
				&face_intersect[0].n,
				&mapvals.lightsource.position,
				&color,
				&mapvals.lightsource.color,
				mapvals.lightsource.type);

           gck_rgba_clamp (&color);
        }
    }
  else
    {
      if (mapvals.transparent_background == TRUE)
        color.a = 0.0;
    }
  
  return color;
}