void psplot_begin_context(
    PSPLOT *p,
    double x_min, double y_min,
    double x_max, double y_max,
    int clip
  )
  {
    if (! p->page_started) { psplot_error("must call begin_page first"); }
    { double x_min_PS = x_center - x_size/2.0;
      double x_max_PS = x_min_PS + x_size;
      double y_min_PS = y_center - y_size/2.0;
      double y_max_PS = y_min_PS + y_size;
      psplot_do_begin_context(p, x_min_PS, x_max_PS, y_min_PS, y_max_PS);
    }
  }
  
void psplot_end_context(PSPLOT *p)
  {
    if (p->epsformat) { psplot_error("illegal in eps file"); }
    if (! p->page_started) { psplot_error("must call begin_page first"); }
    if (! p->context_started) { return; }
    psplot_do_end_context(p);
  }
  
void psplot_setup_page_state(FILE *psfile, int xn, int yn)
  {
    double fxn = xn;
    double fyn = yn;

    fprintf(psfile, "%% Round joints and caps:\n");
    fprintf(psfile, "1 setlinecap 1 setlinejoin\n");
    fprintf(psfile, "\n");

    fprintf(psfile, "%% Black thin lines:\n");
    fprintf(psfile, "0 setlinewidth 0 setgray [ ] 0 setdash\n");
    fprintf(psfile, "\n");

    fprintf(psfile, "/xmin %f def   %% min plottable x\n", x_min_PS);
    fprintf(psfile, "/xmax %f def   %% max plottable x\n", x_max_PS);
    fprintf(psfile, "/xn %d def     %% grid cells along x axis\n", xn);
    fprintf(psfile, "/xstep %f def  %% x-size of grid cell\n", (x_max_PS-x_min_PS)/fxn);

    fprintf(psfile, "/ymin %f def   %% min plottable y\n", y_min_PS);
    fprintf(psfile, "/ymax %f def   %% max plottable y\n", y_max_PS);
    fprintf(psfile, "/yn %d def     %% grid cells along y axis\n", yn);
    fprintf(psfile, "/ystep %f def  %% y-size of grid cell\n", (y_max_PS-y_min_PS)/fyn);

    fprintf(psfile, "%% Units of measure:\n");
    fprintf(psfile, "/pt 1.0 def\n");
    fprintf(psfile, "/in pt 72.0 mul def \n");
    fprintf(psfile, "/mm pt 72.0 25.4 div mul def\n");
    fprintf(psfile, "\n");
    
    psplot_set_label_font (psfile, "Courier", 8.0);    

    fprintf(psfile, "%% Set clipping path to boundary of plot area:\n");
    fprintf(psfile, "newpath\n");
    fprintf(psfile, "  xmin ymin moveto\n");
    fprintf(psfile, "  xmax ymin lineto\n");
    fprintf(psfile, "  xmax ymax lineto\n");
    fprintf(psfile, "  xmin ymax lineto\n");
    fprintf(psfile, "  xmin ymin lineto\n");
    fprintf(psfile, "clip\n");
    fprintf(psfile, "\n");

    fflush(psfile);
  }

void psplot_setup_caption_data(FILE *psfile)
  {
    fprintf(psfile, "%% Caption text cursor:\n");
    fprintf(psfile, "/xtext xmin def\n");
    fprintf(psfile, "/ytext ymin def\n");
    fprintf(psfile, "/dytext 10 pt mul def\n");
    fprintf(psfile, "\n");

    fprintf(psfile, "%% Caption font setup:\n");
    fprintf(psfile, "/captionfont\n");
    fprintf(psfile, "  /Courier findfont\n");
    fprintf(psfile, "  dytext scalefont\n");
    fprintf(psfile, "def\n");
    fprintf(psfile, "\n");
  }


======================================================================

void psplot_end_figure(FILE *psfile)
  {
    psplot_aux_end_page(psfile);
    fprintf(psfile, "%%%%Trailer\n");
    fflush(psfile);
  }

void psplot_save_scales(
    double xmin, double xmax,
    double ymin, double ymax,

    double hmin, double hmax,
    double vmin, double vmax
  )
  {
    x_min_PS = hmin;
    x_max_PS = hmax;
    ps_xmin = xmin;
    ps_xmax = xmax;
    ps_xscale = (hmax - hmin)/(xmax - xmin);

    y_min_PS = vmin;
    y_max_PS = vmax;
    ps_ymin = ymin;
    ps_ymax = ymax;
    ps_yscale = (vmax - vmin)/(ymax - ymin);

    assert (
      (fabs(ps_xscale - ps_yscale)/fabs(ps_xscale + ps_yscale) < 0.0001),
      "psplot_begin_figure: unequal Postscript scales"
    );
  }

======================================================================

/*** PROTOTYPES FOR INTERNAL FUNCTIONS ***/

void ps_aux_polygon(
    FILE *psfile,
    double x[], double y[],
    int npoints,
    double r, double g, double b,
    char *operator
  );


void psplot_aux_rectangle(
    FILE *psfile,
    double xlo, double xhi,
    double ylo, double yhi,
    double gray,
    char *operator
  );
  
void psplot_aux_polygon(
    FILE *psfile,
    double x[], double y[],
    int npoints,
    double gray,
    char *operator
  );

void psplot_aux_circle(
    FILE *psfile,
    double xc, double yc, double radius,
    double gray,
    char *operator
  );
  
void psplot_aux_lune(
    FILE *psfile,
    double xc, double yc, double radius, double tilt,
    double gray,
    char *operator
  );
  
void ps_aux_slice(
    FILE *psfile,
    double xc, double yc, double radius, double start, double stop,
    double r, double g, double b,
    char *operator
  );

  
void psplot_define_procs(FILE *psfile);
void psplot_define_caption_procs(FILE *psfile);

void psplot_save_scales(
    double xmin, double xmax,
    double ymin, double ymax,
    double hmin, double hmax,
    double vmin, double vmax
  );
  
void psplot_setup_page_state(FILE *psfile, int xn, int yn);
void psplot_setup_caption_data(FILE *psfile);
void psplot_aux_end_page(FILE *psfile);

void psplot_put_text(FILE *psfile, char *text, char *newline);

======================================================================
    
    
    int drawing_started;       /* 1 = $do_begin_drawing$ was started. [f] */
    int drawing_state_defined; /* 1 = $do_begin_drawing$ was completed. [f] */


    double y_caption_PS;  /* Y of next caption of current drawing. [d][PS][ex] */

    
        
    
    Some $psplot$ procedures change only certain descriptor fields
    these fields (marked [in] above) comprise the `internal state' of
    the psplot $object$. Other procedures may write Postscript
    commands to the associated $file$, which may change certain
    variables of the Postscript interpreter. Some of those variables
    are mirrored by descriptor fields, marked by [ex], which comprise
    the `external state' of the object.  The remaining fields, marked
    [tv], are derived from the internal and/or external states, and 
    explicitly provided for convenience.
    
    The internal state consists of the nominal ranges for user coordinate
    and the booleans `do_draw', `do_fill', `do_text'.
    
    p->drawing_started = 0;
    p->drawing_state_defined = 0;