void set_scales
  ( PSStream *ps, 
    dg_Interval bbox[],
    double hmin, double hmax, 
    double vmin, double vmax
  );
  /* Adjusts the scales of the Postscript picture stream {ps} so that
    the client rectangle {bbox[0] × bbox[1]} fits snugly (with 
    equal scales) in the plotting area, which is the 
    rectangle {[hmin _ hmax] × [vmin _ vmax]}, in pt,
    relative to the lower left corner of the figure.  */

void set_scales
  ( PSStream *ps, 
    dg_Interval bbox[],
    double hmin, double hmax, 
    double vmin, double vmax
  )
  { /* Fit {bbox} in the given plot window, with equal scales for X and Y. */
    double xc = (bbox[0].end[BLO] + bbox[0].end[BHI])/2;
    double yc = (bbox[1].end[BLO] + bbox[1].end[BHI])/2;
    double wx = (bbox[0].end[BHI] - bbox[0].end[BLO])/2;
    double wy = (bbox[1].end[BHI] - bbox[1].end[BLO])/2;

    double wh = (hmax - hmin)/2;
    double wv = (vmax - vmin)/2;
    
    double scale = 1.02 * (wx/wh > wy/wv ? wx/wh : wy/wv);
    
    double xmin = xc - wh*scale, xmax = xc + wh*scale;
    double ymin = yc - wv*scale, ymax = yc + wv*scale;
    
    pswr_set_window
      ( ps,
        xmin, xmax, ymin, ymax, 
        hmin, hmax, vmin, vmax,
        1,1
      );
  }