FILE* svgBegin(const char *filename, double widthMM, double heightMM, double unitsPerMM) {

  FILE *f = fopen(filename, "w");

  if (f) {

    fprintf(f, "<svg width=\"%gmm\" height=\"%gmm\" viewBox=\"0 0 %g %g\">\n",

               widthMM, heightMM, widthMM*unitsPerMM, heightMM*unitsPerMM );

  }

  return f;

}

void svgEnd(FILE *f)  {

  if (!f) return;

  fprintf(f, "</svg>\n");

  fclose(f);

}

void svgAddText(FILE *f, double x, double y, double size, const char *text)  {

  if (!f) return;

  fprintf(f, "<text x=\"%g\" y=\"%g\" style=\"font-size:%g\">%s</text>\n", x, y, size, text);

}

void svgAddPath(FILE *f, const char *path, double width, int round)  {

  if (!f) return;

  fprintf(f, "

             "      d=\"%s\" />\n",

             (round ? "stroke-linecap:round;stroke-linejoin:round;" : ""),

             width, path );

}