---

gromacsplugin.C

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/***************************************************************************
 *cr
 *cr            (C) Copyright 1995-2016 The Board of Trustees of the
 *cr                        University of Illinois
 *cr                         All Rights Reserved
 *cr
 ***************************************************************************/

/***************************************************************************
 * RCS INFORMATION:
 *
 *      $RCSfile: gromacsplugin.C,v $
 *      $Author: johns $       $Locker:  $             $State: Exp $
 *      $Revision: 1.54 $       $Date: 2017/05/20 05:37:53 $
 *
 ***************************************************************************/

#include "largefiles.h"   /* platform dependent 64-bit file I/O defines */

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "Gromacs.h"
#include "molfile_plugin.h"

#if defined(_AIX)
#include <strings.h>
#endif

#ifndef M_PI
#define M_PI           3.14159265358979323846
#endif

#if defined(WIN32) || defined(WIN64)
#define strcasecmp stricmp
#endif

typedef struct {
  md_file *mf;
  int natoms;
  int step;
  float timeval;
  molfile_atom_t *atomlist;
  molfile_metadata_t *meta;
} gmxdata;

static void convert_vmd_box_for_writing(const molfile_timestep_t *ts, float *x, float *y, float *z)
{
//     const float sa = sin((double)ts->alpha/180.0*M_PI);
    const float ca = cos((double)ts->alpha/180.0*M_PI);
    const float cb = cos((double)ts->beta/180.0*M_PI);
    const float cg = cos((double)ts->gamma/180.0*M_PI);
    const float sg = sin((double)ts->gamma/180.0*M_PI);

    x[0] = ts->A / ANGS_PER_NM;
    y[0] = 0.0;
    z[0] = 0.0;
    x[1] = ts->B*cg / ANGS_PER_NM; // ts->B*ca when writing trr?!
    y[1] = ts->B*sg / ANGS_PER_NM; // ts->B*sa when writing trr?!
    z[1] = 0.0;
    x[2] = ts->C*cb / ANGS_PER_NM;
    y[2] = (ts->C / ANGS_PER_NM)*(ca - cb*cg)/sg;
    z[2] = (ts->C / ANGS_PER_NM)*sqrt((double)(1.0 + 2.0*ca*cb*cg
                               - ca*ca - cb*cb - cg*cg)/(1.0 - cg*cg));
}

static void *open_gro_read(const char *filename, const char *,
    int *natoms) {

    md_file *mf;
    md_header mdh;
    gmxdata *gmx;

    mf = mdio_open(filename, MDFMT_GRO);
    if (!mf) {
        fprintf(stderr, "gromacsplugin) Cannot open file '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
        return NULL;
    }

    // read in the header data (careful not to rewind!)
    if (gro_header(mf, mdh.title, MAX_MDIO_TITLE,
    &mdh.timeval, &mdh.natoms, 0) < 0) {
        fprintf(stderr, "gromacsplugin) Cannot read header fromm '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
            // XXX should free the file handle...
        return NULL;
    }
    *natoms = mdh.natoms;
    gmx = new gmxdata;
    memset(gmx,0,sizeof(gmxdata));
    gmx->mf = mf;
    gmx->natoms = mdh.natoms;
    gmx->meta = new molfile_metadata_t;
    memset(gmx->meta,0,sizeof(molfile_metadata_t));
    strncpy(gmx->meta->title, mdh.title, 80);
    gmx->timeval = mdh.timeval;
    return gmx;
}

static int read_gro_structure(void *mydata, int *optflags,
    molfile_atom_t *atoms) {

  md_atom ma;
  char buf[MAX_GRO_LINE + 1];
  gmxdata *gmx = (gmxdata *)mydata;

  *optflags = MOLFILE_NOOPTIONS; // no optional data

  // read in each atom and add it into the molecule
  for (int i = 0; i < gmx->natoms; i++) {
    molfile_atom_t *atom = atoms+i;
    if (gro_rec(gmx->mf, &ma) < 0) {
      fprintf(stderr, "gromacsplugin) Error reading atom %d from file, %s\n",
              i+1, mdio_errmsg(mdio_errno()));
      return MOLFILE_ERROR;
    }
    strcpy(atom->name, ma.atomname);
    strcpy(atom->type, ma.atomname);
    strcpy(atom->resname, ma.resname);
    atom->resid = atoi(ma.resid);
    atom->chain[0] = '\0';
    atom->segid[0] = '\0';
  }

  if (mdio_readline(gmx->mf, buf, MAX_GRO_LINE + 1, 0) < 0) {
    fprintf(stderr, "gromacsplugin) Warning, error reading box, %s\n",
            mdio_errmsg(mdio_errno()));
  }

  rewind(gmx->mf->f);
  return MOLFILE_SUCCESS;
}

static int read_gro_molecule_metadata(void *v, molfile_metadata_t **metadata) {
  gmxdata *gmx = (gmxdata *)v;
  *metadata = gmx->meta;
  return MOLFILE_SUCCESS;
}

static int read_gro_timestep(void *v, int natoms, molfile_timestep_t *ts) {
  gmxdata *gmx = (gmxdata *)v;
  md_ts mdts;
  memset(&mdts, 0, sizeof(md_ts));
  mdts.natoms = natoms;

  if (mdio_timestep(gmx->mf, &mdts) < 0)
    return MOLFILE_ERROR;
  if (ts) {
    memcpy(ts->coords, mdts.pos, 3 * sizeof(float) * gmx->natoms);
    if (mdts.box) {
      ts->A = mdts.box->A;
      ts->B = mdts.box->B;
      ts->C = mdts.box->C;
      ts->alpha = mdts.box->alpha;
      ts->beta = mdts.box->beta;
      ts->gamma = mdts.box->gamma;
    }
  }
  mdio_tsfree(&mdts);
  return MOLFILE_SUCCESS;
}

static void close_gro_read(void *v) {
  gmxdata *gmx = (gmxdata *)v;
  mdio_close(gmx->mf);
  delete gmx->meta;
  delete gmx;
}

// open file for writing
static void *open_gro_write(const char *filename, const char *filetype,
    int natoms) {

    md_file *mf;
    gmxdata *gmx;

    mf = mdio_open(filename, MDFMT_GRO, MDIO_WRITE);
    if (!mf) {
        fprintf(stderr, "gromacsplugin) Cannot open file '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
        return NULL;
    }
    gmx = new gmxdata;
    memset(gmx,0,sizeof(gmxdata));
    gmx->mf = mf;
    gmx->natoms = natoms;
    gmx->step   = 0;
    gmx->meta = new molfile_metadata_t;
    memset(gmx->meta,0,sizeof(molfile_metadata_t));
    gmx->meta->title[0] = '\0';

    return gmx;
}

static int write_gro_structure(void *v, int optflags,
    const molfile_atom_t *atoms) {

  gmxdata *gmx = (gmxdata *)v;
  int natoms = gmx->natoms;
  gmx->atomlist = (molfile_atom_t *)malloc(natoms*sizeof(molfile_atom_t));
  memcpy(gmx->atomlist, atoms, natoms*sizeof(molfile_atom_t));

  return MOLFILE_SUCCESS;
}

static int write_gro_timestep(void *v, const molfile_timestep_t *ts) {
  gmxdata *gmx = (gmxdata *)v;
  const molfile_atom_t *atom;
  const float *pos, *vel;
  float x[3], y[3], z[3];
  int i;

  if (gmx->natoms == 0)
    return MOLFILE_SUCCESS;

  atom = gmx->atomlist;
  pos = ts->coords;
  vel = ts->velocities;

  /* The title cannot be written */
/*  fprintf(gmx->mf->f, "%s", gmx->meta->title);*/
  /* Write a dummy title instead */
  fprintf(gmx->mf->f, "generated by VMD");
#if vmdplugin_ABIVERSION > 10
  fprintf(gmx->mf->f, ", t= %f", ts->physical_time);
#endif
  fprintf(gmx->mf->f, "\n");

  fprintf(gmx->mf->f, "%d\n", gmx->natoms);
  for (i=0; i<gmx->natoms; i++)
  {
     fprintf(gmx->mf->f, "%5d%-5s%5s%5d%8.3f%8.3f%8.3f",
             atom->resid, atom->resname, atom->name,
             (i+1) % 100000, // GRO format only supports indices up to 99999
                             // but since GROMACS ignores indices, modular
                             // arithmetic prevents formatting problems for 
                             // very large structures
             pos[0] / ANGS_PER_NM, pos[1] / ANGS_PER_NM, pos[2] / ANGS_PER_NM);
     if(vel)
     {
         fprintf(gmx->mf->f, "%8.4f%8.4f%8.4f", vel[0] / ANGS_PER_NM, vel[1] / ANGS_PER_NM, vel[2] / ANGS_PER_NM);
         vel += 3;
     }
     fprintf(gmx->mf->f, "\n");
     ++atom;
     pos += 3;
  }
  convert_vmd_box_for_writing(ts, x, y, z);
  fprintf(gmx->mf->f, "%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f%10.5f\n", x[0], y[1], z[2], y[0], z[0], x[1], z[1], x[2], y[2]);

  return MOLFILE_SUCCESS;
}

static void close_gro_write(void *v) {
  gmxdata *gmx = (gmxdata *)v;
  mdio_close(gmx->mf);
  free(gmx->atomlist);
  delete gmx->meta;
  delete gmx;
}


static void *open_g96_read(const char *filename, const char *,
    int *natoms) {

    md_file *mf;
    md_header mdh;
    char gbuf[MAX_G96_LINE + 1];

    mf = mdio_open(filename, MDFMT_G96);
    if (!mf) {
        fprintf(stderr, "gromacsplugin) Cannot open file '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
        return NULL;
    }

        // read in the header data
        if (g96_header(mf, mdh.title, MAX_MDIO_TITLE, &mdh.timeval) < 0) {
            fprintf(stderr, "gromacsplugin) Cannot read header from '%s', %s\n",
                    filename, mdio_errmsg(mdio_errno()));
            return NULL;
        }

        // First, look for a timestep block
        if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0) {
            fprintf(stderr, "gromacsplugin) Cannot read header from '%s', %s\n",
                    filename, mdio_errmsg(mdio_errno()));
            return NULL;
        }
        if (!strcasecmp(gbuf, "TIMESTEP")) {
            // Read in the value line and the END line, and the next
            if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0 ||
                mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0 ||
                mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0) {
              fprintf(stderr, "gromacsplugin) Cannot read header from '%s', %s\n",
                      filename, mdio_errmsg(mdio_errno()));
              return NULL;
            }
        }
        if (strcasecmp(gbuf, "POSITION") && strcasecmp(gbuf, "REFPOSITION")) {
          fprintf(stderr, "gromacsplugin) No structure information in file %s\n", filename);
          return NULL;
        }
        *natoms = g96_countatoms(mf);

        gmxdata *gmx = new gmxdata;
        memset(gmx,0,sizeof(gmxdata));
        gmx->mf = mf;
        gmx->natoms = *natoms; 
        return gmx;
}

static int read_g96_structure(void *mydata, int *optflags,
    molfile_atom_t *atoms) {

    char gbuf[MAX_G96_LINE + 1];
    gmxdata *gmx = (gmxdata *)mydata;
    md_atom ma;
    md_file *mf = gmx->mf;

    *optflags = MOLFILE_NOOPTIONS; // no optional data

        for (int i = 0; i < gmx->natoms; i++) {
            molfile_atom_t *atom = atoms+i;
            if (g96_rec(mf, &ma) < 0) {
                fprintf(stderr, "gromacsplugin) Error reading atom %d from file, %s\n",
                  i+1, mdio_errmsg(mdio_errno()));
                return MOLFILE_ERROR;
            }
            strcpy(atom->name, ma.atomname);
            strcpy(atom->type, ma.atomname);
            strcpy(atom->resname, ma.resname);
            atom->resid = atoi(ma.resid);
            atom->chain[0] = '\0';
            atom->segid[0] = '\0';
        }

        if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0) {
            fprintf(stderr, "gromacsplugin) Warning, error reading END record, %s\n",
                mdio_errmsg(mdio_errno()));
        }

            // ... another problem: there may or may not be a VELOCITY
            // block or a BOX block, so we need to read one line beyond
            // the POSITION block to determine this. If neither VEL. nor
            // BOX are present we've read a line too far and infringed
            // on the next timestep, so we need to keep track of the
            // position now for a possible fseek() later to backtrack.
            long fpos = ftell(mf->f);

            // Now we must read in the velocities and the box, if present
            if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) >= 0) {

                // Is there a velocity block present ?
                if (!strcasecmp(gbuf, "VELOCITY") || !strcasecmp(gbuf, "VELOCITYRED")) {
                        // Ignore all the coordinates - VMD doesn't use them
                        for (;;) {
                                if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0)
                                        return MOLFILE_ERROR;
                                if (!strcasecmp(gbuf, "END")) break;
                        }

                        // Again, record our position because we may need
                        // to fseek here later if we read too far.
                        fpos = ftell(mf->f);

                        // Go ahead and read the next line.
                        if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0)
                    return MOLFILE_ERROR;
                }

                // Is there a box present ?
                if (!strcasecmp(gbuf, "BOX")) {
                        // Ignore the box coordinates at this time.
                        if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0)
                    return MOLFILE_ERROR;
                        if (mdio_readline(mf, gbuf, MAX_G96_LINE + 1) < 0)
                    return MOLFILE_ERROR;
                        if (strcasecmp(gbuf, "END"))
                    return MOLFILE_ERROR;
                }
                else {
                        // We have read too far, so fseek back to the
                        // last known safe position so we don't return
                        // with the file pointer set infringing on the
                        // next timestep data.
                        fseek(mf->f, fpos, SEEK_SET);
                }
        }
        else {
            // Go ahead and rewind for good measure
            fseek(mf->f, fpos, SEEK_SET);
        }
        rewind(mf->f);
        return MOLFILE_SUCCESS;
}

static int read_g96_timestep(void *v, int natoms, molfile_timestep_t *ts) {

  gmxdata *gmx = (gmxdata *)v;
  md_ts mdts;
  memset(&mdts, 0, sizeof(md_ts));
  mdts.natoms = natoms;

  if (mdio_timestep(gmx->mf, &mdts) < 0)
    return MOLFILE_ERROR;
  if (ts) {
    memcpy(ts->coords, mdts.pos, 3 * sizeof(float) * gmx->natoms);
    if (mdts.box) {
      ts->A = mdts.box->A;
      ts->B = mdts.box->B;
      ts->C = mdts.box->C;
      ts->alpha = mdts.box->alpha;
      ts->beta = mdts.box->beta;
      ts->gamma = mdts.box->gamma;
    }
  }
  mdio_tsfree(&mdts);
  return MOLFILE_SUCCESS;
}

static void close_g96_read(void *v) {
  gmxdata *gmx = (gmxdata *)v;
  mdio_close(gmx->mf);
  delete gmx;
}


//
// TRR and XTC files
//

static void *open_trr_read(const char *filename, const char *filetype,
    int *natoms) {

    md_file *mf;
    md_header mdh;
    gmxdata *gmx;
    int format;

    if (!strcmp(filetype, "trr"))
      format = MDFMT_TRR;
    else if (!strcmp(filetype, "trj"))
      format = MDFMT_TRJ;
    else if (!strcmp(filetype, "xtc"))
      format = MDFMT_XTC;
    else
      return NULL;

    mf = mdio_open(filename, format);
    if (!mf) {
        fprintf(stderr, "gromacsplugin) Cannot open file '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
        return NULL;
    }
    if (mdio_header(mf, &mdh) < 0) {
        mdio_close(mf);
        fprintf(stderr, "gromacsplugin) Cannot read header fromm '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
        return NULL;
    }
    *natoms = mdh.natoms;
    gmx = new gmxdata;
    memset(gmx,0,sizeof(gmxdata));
    gmx->mf = mf;
    gmx->natoms = mdh.natoms;
    return gmx;
}

static int read_trr_timestep(void *v, int natoms, molfile_timestep_t *ts) {
  gmxdata *gmx = (gmxdata *)v;
  md_ts mdts;
  memset(&mdts, 0, sizeof(md_ts));
  mdts.natoms = natoms;

  if (mdio_timestep(gmx->mf, &mdts) < 0) {
    if (mdio_errno() == MDIO_EOF || mdio_errno() == MDIO_IOERROR) {
      // XXX Lame, why does mdio treat IOERROR like EOF?
      return MOLFILE_ERROR;
    }
    fprintf(stderr, "gromacsplugin) Error reading timestep, %s\n",
            mdio_errmsg(mdio_errno()));
    return MOLFILE_ERROR;
  }
  if (mdts.natoms != gmx->natoms) {
    fprintf(stderr, "gromacsplugin) Timestep in file contains wrong number of atoms\n");
    fprintf(stderr, "gromacsplugin) Found %d, expected %d\n", mdts.natoms, gmx->natoms);
    mdio_tsfree(&mdts);
    return MOLFILE_ERROR;
  }

  if (ts) {
    if (mdts.pos) 
      memcpy(ts->coords, mdts.pos, 3 * sizeof(float) * gmx->natoms);
    else 
      printf("gromacsplugin) Warning: skipping empty timestep!\n");

    if (mdts.box) {
      ts->A = mdts.box->A;
      ts->B = mdts.box->B;
      ts->C = mdts.box->C;
      ts->alpha = mdts.box->alpha;
      ts->beta = mdts.box->beta;
      ts->gamma = mdts.box->gamma;
    }
  }
  mdio_tsfree(&mdts);
  return MOLFILE_SUCCESS;
}

static void close_trr_read(void *v) {
  gmxdata *gmx = (gmxdata *)v;
  mdio_close(gmx->mf);
  delete gmx;
}

// open file for writing
static void *open_trr_write(const char *filename, const char *filetype,
    int natoms) {

    md_file *mf;
    gmxdata *gmx;
    int format;

    if (!strcmp(filetype, "trr"))
      format = MDFMT_TRR;
    else if (!strcmp(filetype, "xtc"))
      format = MDFMT_XTC;
    else
      return NULL;

    mf = mdio_open(filename, format, MDIO_WRITE);
    if (!mf) {
        fprintf(stderr, "gromacsplugin) Cannot open file '%s', %s\n",
                filename, mdio_errmsg(mdio_errno()));
        return NULL;
    }
    gmx = new gmxdata;
    memset(gmx,0,sizeof(gmxdata));
    gmx->mf = mf;
    gmx->natoms = natoms;
    // set some parameters for the output stream:
    // start at step 0, convert to big-endian, write single precision.
    gmx->step   = 0;
    gmx->mf->rev = host_is_little_endian();
    gmx->mf->prec = sizeof(float);
    return gmx;
}

// write a trr timestep. the file format has a header with each record
static int write_trr_timestep(void *mydata, const molfile_timestep_t *ts)
{
  const float nm=0.1;

  gmxdata *gmx = (gmxdata *)mydata;

  // determine and write header from structure info.
  // write trr header. XXX: move this to Gromacs.h ??
  if (gmx->mf->fmt == MDFMT_TRR) {
    int i;

    if ( put_trx_int(gmx->mf, TRX_MAGIC)            // ID
         || put_trx_string(gmx->mf, "GMX_trn_file") // version
         || put_trx_int(gmx->mf, 0)                 // ir_size (ignored)
         || put_trx_int(gmx->mf, 0)                 // e_size (ignored)
         || put_trx_int(gmx->mf, 9*sizeof(float))   // box
         || put_trx_int(gmx->mf, 0)                 // vir_size (ignored)
         || put_trx_int(gmx->mf, 0)                 // pres_size (ignored)
         || put_trx_int(gmx->mf, 0)                 // top_size (ignored)
         || put_trx_int(gmx->mf, 0)                 // sym_size (ignored)
         || put_trx_int(gmx->mf, 3*sizeof(float)*gmx->natoms) // coordinates
         || put_trx_int(gmx->mf, 0)                 // no velocities
         || put_trx_int(gmx->mf, 0)                 // no forces
         || put_trx_int(gmx->mf, gmx->natoms)       // number of atoms
         || put_trx_int(gmx->mf, gmx->step)         // current step number
         || put_trx_int(gmx->mf, 0)                 // nre (ignored)
         || put_trx_real(gmx->mf, 0.1*gmx->step)    // current time. (dummy value: 0.1)
         || put_trx_real(gmx->mf, 0.0))             // current lambda
      return MOLFILE_ERROR;

    // set up box according to the VMD unitcell conventions.
    // the a-vector is collinear with the x-axis and
    // the b-vector is in the xy-plane.
    const float sa = sin((double)ts->alpha/180.0*M_PI);
    const float ca = cos((double)ts->alpha/180.0*M_PI);
    const float cb = cos((double)ts->beta/180.0*M_PI);
    const float cg = cos((double)ts->gamma/180.0*M_PI);
    const float sg = sin((double)ts->gamma/180.0*M_PI);
    float box[9];
    box[0] = ts->A;    box[1] = 0.0;      box[2] = 0.0;
    box[3] = ts->B*ca; box[4] = ts->B*sa; box[5] = 0.0;
    box[6] = ts->C*cb; box[7] = ts->C*(ca - cb*cg)/sg;
    box[8] = ts->C*sqrt((double)(1.0 + 2.0*ca*cb*cg
                                 - ca*ca - cb*cb - cg*cg)/(1.0 - cg*cg));

    for (i=0; i<9; ++i) {
      if (put_trx_real(gmx->mf, box[i]*nm))
        return MOLFILE_ERROR;
    }
#ifdef TEST_TRR_PLUGIN
    fprintf(stderr, "gromacsplugin) box is:\n %f %f %f\n %f %f %f\n %f %f %f\n\n",
            box[0], box[1], box[2], box[3], box[4], box[5], box[6], box[7], box[8]);
#endif

    // write coordinates
    for (i=0; i<(3*gmx->natoms); ++i) {
      if (put_trx_real(gmx->mf, ts->coords[i]*nm))
        return MOLFILE_ERROR;
    }
  } else {
    fprintf(stderr, "gromacsplugin) only .trr is supported for writing\n");
    return MOLFILE_ERROR;
  }

  ++ gmx->step;
  return MOLFILE_SUCCESS;
  }


static void close_trr_write(void *v) {
  gmxdata *gmx = (gmxdata *)v;
  mdio_close(gmx->mf);
  delete gmx;
}

#define GROMACS_PLUGIN_MAJOR_VERSION 1
#define GROMACS_PLUGIN_MINOR_VERSION 3 

//
// plugin registration stuff below
//

static molfile_plugin_t gro_plugin;
static molfile_plugin_t g96_plugin;
static molfile_plugin_t trr_plugin;
static molfile_plugin_t xtc_plugin;
static molfile_plugin_t trj_plugin;


VMDPLUGIN_API int VMDPLUGIN_init() {
  // GRO plugin init
  memset(&gro_plugin, 0, sizeof(molfile_plugin_t));
  gro_plugin.abiversion = vmdplugin_ABIVERSION;
  gro_plugin.type = MOLFILE_PLUGIN_TYPE;
  gro_plugin.name = "gro";
  gro_plugin.prettyname = "Gromacs GRO";
  gro_plugin.author = "David Norris, Justin Gullingsrud, Magnus Lundborg";
  gro_plugin.majorv = GROMACS_PLUGIN_MAJOR_VERSION;
  gro_plugin.minorv = GROMACS_PLUGIN_MINOR_VERSION;
  gro_plugin.is_reentrant = VMDPLUGIN_THREADUNSAFE;
  gro_plugin.filename_extension = "gro";
  gro_plugin.open_file_read = open_gro_read;
  gro_plugin.read_structure = read_gro_structure;
  gro_plugin.read_next_timestep = read_gro_timestep;
  gro_plugin.close_file_read = close_gro_read;
  gro_plugin.open_file_write = open_gro_write;
  gro_plugin.write_structure = write_gro_structure;
  gro_plugin.write_timestep = write_gro_timestep;
  gro_plugin.close_file_write = close_gro_write;
  gro_plugin.read_molecule_metadata = read_gro_molecule_metadata;

  // G96 plugin init
  memset(&g96_plugin, 0, sizeof(molfile_plugin_t));
  g96_plugin.abiversion = vmdplugin_ABIVERSION;
  g96_plugin.type = MOLFILE_PLUGIN_TYPE;
  g96_plugin.name = "g96";
  g96_plugin.prettyname = "Gromacs g96";
  g96_plugin.author = "David Norris, Justin Gullingsrud";
  g96_plugin.majorv = GROMACS_PLUGIN_MAJOR_VERSION;
  g96_plugin.minorv = GROMACS_PLUGIN_MINOR_VERSION;
  g96_plugin.is_reentrant = VMDPLUGIN_THREADUNSAFE;
  g96_plugin.filename_extension = "g96";
  g96_plugin.open_file_read = open_g96_read;
  g96_plugin.read_structure = read_g96_structure;
  g96_plugin.read_next_timestep = read_g96_timestep;
  g96_plugin.close_file_read = close_g96_read;

  // TRR plugin
  memset(&trr_plugin, 0, sizeof(molfile_plugin_t));
  trr_plugin.abiversion = vmdplugin_ABIVERSION;
  trr_plugin.type = MOLFILE_PLUGIN_TYPE;
  trr_plugin.name = "trr";
  trr_plugin.prettyname = "Gromacs TRR Trajectory";
  trr_plugin.author = "David Norris, Justin Gullingsrud, Axel Kohlmeyer";
  trr_plugin.majorv = GROMACS_PLUGIN_MAJOR_VERSION;
  trr_plugin.minorv = GROMACS_PLUGIN_MINOR_VERSION;
  trr_plugin.is_reentrant = VMDPLUGIN_THREADUNSAFE;
  trr_plugin.filename_extension = "trr";
  trr_plugin.open_file_read = open_trr_read;
  trr_plugin.read_next_timestep = read_trr_timestep;
  trr_plugin.close_file_read = close_trr_read;
  trr_plugin.open_file_write = open_trr_write;
  trr_plugin.write_timestep = write_trr_timestep;
  trr_plugin.close_file_write = close_trr_write;

  // XTC plugin 
  memset(&xtc_plugin, 0, sizeof(molfile_plugin_t));
  xtc_plugin.abiversion = vmdplugin_ABIVERSION;
  xtc_plugin.type = MOLFILE_PLUGIN_TYPE;
  xtc_plugin.name = "xtc";
  xtc_plugin.prettyname = "Gromacs XTC Compressed Trajectory";
  xtc_plugin.author = "David Norris, Justin Gullingsrud";
  xtc_plugin.majorv = GROMACS_PLUGIN_MAJOR_VERSION;
  xtc_plugin.minorv = GROMACS_PLUGIN_MINOR_VERSION;
  xtc_plugin.is_reentrant = VMDPLUGIN_THREADUNSAFE;
  xtc_plugin.filename_extension = "xtc";
  xtc_plugin.open_file_read = open_trr_read;
  xtc_plugin.read_next_timestep = read_trr_timestep;
  xtc_plugin.close_file_read = close_trr_read;

  // TRJ plugin
  memset(&trj_plugin, 0, sizeof(molfile_plugin_t));
  trj_plugin.abiversion = vmdplugin_ABIVERSION;
  trj_plugin.type = MOLFILE_PLUGIN_TYPE;
  trj_plugin.name = "trj";
  trj_plugin.prettyname = "Gromacs TRJ Trajectory";
  trj_plugin.author = "David Norris, Justin Gullingsrud";
  trj_plugin.majorv = GROMACS_PLUGIN_MAJOR_VERSION;
  trj_plugin.minorv = GROMACS_PLUGIN_MINOR_VERSION;
  trj_plugin.is_reentrant = VMDPLUGIN_THREADUNSAFE;
  trj_plugin.filename_extension = "trj";
  trj_plugin.open_file_read = open_trr_read;
  trj_plugin.read_next_timestep = read_trr_timestep;
  trj_plugin.close_file_read = close_trr_read;

  return 0;
}

VMDPLUGIN_API int VMDPLUGIN_register(void *v, vmdplugin_register_cb cb) {
  (*cb)(v, (vmdplugin_t *)&gro_plugin);
  (*cb)(v, (vmdplugin_t *)&g96_plugin);
  (*cb)(v, (vmdplugin_t *)&trr_plugin);
  (*cb)(v, (vmdplugin_t *)&trj_plugin);
  (*cb)(v, (vmdplugin_t *)&xtc_plugin);
  return 0;
}

VMDPLUGIN_API int VMDPLUGIN_fini() {
  return 0;
}


#ifdef TEST_G96_PLUGIN

int main(int argc, char *argv[]) {
  int natoms;

  molfile_timestep_t timestep;
  void *v;
  int i;

  if (argc < 2) return 1;
  while (--argc) {
    ++argv;
    v = open_g96_read(*argv, "g96", &natoms);
    if (!v) {
      fprintf(stderr, "open_g96_read failed for file %s\n", *argv);
      return 1;
    }
    timestep.coords = (float *)malloc(3*sizeof(float)*natoms);
    i = 0;
    while(!read_g96_timestep(v, natoms, &timestep)) {
      ++i;
    }
    fprintf(stderr, "ended read_g96_timestep on step %d\n", i);
    free(timestep.coords);
    close_g96_read(v);
  }
  return 0;
}

#endif

#ifdef TEST_TRR_PLUGIN

int main(int argc, char *argv[]) {
  int natoms;

  molfile_timestep_t timestep;
  void *v, *w;
  int i;

  if (argc != 3) return 1;
  v = open_trr_read(argv[1], "trr", &natoms);
  if (!v) {
    fprintf(stderr, "open_trr_read failed for file %s\n", argv[1]);
    return 1;
  }
  timestep.coords = (float *)malloc(3*sizeof(float)*natoms);
  w = open_trr_write(argv[2], "trr", natoms);
  if (!w) {
    fprintf(stderr, "open_trr_write failed for file %s\n", argv[2]);
    return 1;
  }

  i = 0;
  while(!read_trr_timestep(v, natoms, &timestep)) {
    ++i;
    if (write_trr_timestep(w, &timestep)) {
      fprintf(stderr, "write error\n");
      return 1;
    }
  }

  fprintf(stderr, "ended read_trr_timestep on step %d\n", i);
  free(timestep.coords);
  close_trr_read(v);
  close_trr_write(w);
  return 0;
}

#endif

---