Function:ns2texpoly3d

 void ns2texpoly3d(XYZ *iP, XYZ *iTC, float in, unsigned int texid, char itrans, float ialpha);

#include <stdio.h>
#include <stdlib.h>
#include "s2plot.h"

unsigned int texid;                             /* 3D Texture ID */

void cb(double *t, int *kc)
{
   int nverts = 4;                              /* Number of vertices in polygon */
   char trans = 't';                            /* 3d texture transparency */
   float alpha = 0.7;                           /* Alpha channel value */

   XYZ iP[4];                                   /* Array of polygon vertices */
   XYZ iTC[4];                                  /* Array of texture coordinates */
   static float texidx = 0.0;                   /* Current z-texture coordinate */

   iP[0].x = iP[3].x = -1.0;                    /* Define polygon vertices */
   iP[1].x = iP[2].x = +1.0;
   iP[0].y = iP[1].y = +1.0;
   iP[2].y = iP[3].y = -1.0;
   iP[0].z = iP[1].z = iP[2].z = iP[3].z = texidx*2.0 - 1.0;

   iTC[0].x = iTC[3].x = 0.0;                   /* Define texture coordinates */
   iTC[1].x = iTC[2].x = 1.0;
   iTC[0].y = iTC[1].y = 1.0;
   iTC[2].y = iTC[3].y = 0.0;
   iTC[0].z = iTC[1].z = iTC[2].z = iTC[3].z = texidx;

   COLOUR col = { 1,1,1 };                      /* Draw the polygon boundaries */
   ns2vline(iP[0],iP[1],col);
   ns2vline(iP[1],iP[2],col);
   ns2vline(iP[2],iP[3],col);
   ns2vline(iP[3],iP[0],col);

   ns2texpoly3d(iP, iTC, nverts, texid, trans, alpha);  /* Draw 3D texture */

   texidx += (1.0/320.0);                       /* Choose next z-texture coordinate */
   if (texidx > 1.0) texidx = 0.0;
}

int main(int argc, char *argv[])
{
   int Nx = 32, Ny = 32, Nz = 32;               /* Texture dimensions */
   int w,h,d;                                   /* Returned dimensions */

   s2opend("/?",argc,argv);                     /* Open the s2plot display device */
   s2swin(-1,1,-1,1,-1,1);                      /* Set the world coordinates */
   s2box("BCDET",0,0,"BCDET",0,0,"BCDET",0,0);

   texid = ss2c3dt(Nx, Ny, Nz);                 /* Create a new 3d texture */
   unsigned char *bits = (unsigned char *)ss2g3dt(texid, &w, &h, &d);
                                                /* Get the texture data for modification */
   int i, j, k;
   long idx;
   float x,y,z;
   for (i=0;i<Nx;i++) {
      x = -1.0 + i*(2.0/(float)(Nx-1));
      for (j=0;j<Ny;j++) {
         y = -1.0 + j*(2.0/(float)(Ny-1));
         for (k=0;k<Nz;k++) {
            z = -1.0 + k*(2.0/(float)(Nz-1));
            idx = ((i*Ny + j)*Nz + k)*4;
            if ((x*x + y*y + z*z) < 1.0) {      /* 3D solid red sphere */
               bits[idx + 1 ] = 255;
               ns2point(x,y,z,1,1,1);           /* Plot point in sphere */
            } else {
               bits[idx + 0 ] = 0;
            }

            bits[idx + 1 ] = 0;                 /* Blue channel */
            bits[idx + 2 ] = 0;                 /* Green channel */
            bits[idx + 3 ] = 255;               /* Alpha channel */
         }
      }
   }

   fprintf(stderr, "3d texture IS %d x %d x %d\n", w, h, d);
   ss2pt(texid);                                /* Push back the texture */

   cs2scb(cb);                                  /* Install a dynamic callback */

   s2show(1);                                   /* Display the geometry */

   return 0;
}