void hedge_draw_edge(epswr_figure_t *eps, hedge_arc_t *a, char *laba, char *labb, bool_t nodes)
  { 
    hedge_arc_t *b = a->twin;
    hedge_vert_t *org = a->org;
    hedge_vert_t *dst = b->org;
    
    if ((! org->show) && (! dst->show)) { return; } 
  
    /* Bézier control points for edge proper: */
    double p1x, p1y, p2x, p2y;
    hedge_draw_get_edge_bezier_points(a, &p1x, &p1y, &p2x, &p2y);
    
    if (nodes)
      { /* Draw the node boxes and links, with labels: */
        hedge_draw_arc_record(eps, a, p1x, p1y, p2x, p2y, laba);
        hedge_draw_arc_record(eps, b, p2x, p2y, p1x, p1y, labb);
      }
    else
      { double p0x = org->pos.c[0], p0y = org->pos.c[1]; 
        double p3x = dst->pos.c[0], p3y = dst->pos.c[1]; 
        if ((laba == NULL) && (labb == NULL))
          { /* Draw the actual edge: */
            epswr_curve(eps, p0x, p0y, p1x, p1y, p2x, p2y, p3x, p3y);
          }
        else
          { /* Draw arrowheads on edge and labels: */
            if (laba != NULL)
              { hedge_draw_arc_arrow(eps, p0x, p0y, p1x, p1y, p2x, p2y, p3x, p3y);
                hedge_draw_arc_label(eps, p0x, p0y, p1x, p1y, p2x, p2y, p3x, p3y, laba);
              }
            if (labb != NULL)
              { hedge_draw_arc_arrow(eps, p3x, p3y, p2x, p2y, p1x, p1y, p0x, p0y);
                hedge_draw_arc_label(eps, p3x, p3y, p2x, p2y, p1x, p1y, p0x, p0y, labb);
              }
          }
       }
  }


void hedge_draw_arc_label
  ( epswr_figure_t *eps,
    double p0x, double p0y,
    double p1x, double p1y,
    double p2x, double p2y,
    double p3x, double p3y,
    char *lab
  )
  { double t = 0.3; /* Label position along arg. */
    double x, dx; hedge_draw_bezier_eval(t, p0x, p1x, p2x, p3x, &x, &dx);
    double y, dy; hedge_draw_bezier_eval(t, p0y, p1y, p2y, p3y, &y, &dy);
    double hAlign, vAlign;
    hedge_draw_choose_arc_lab_align(dx, dy, &hAlign, &vAlign);
    if (lab != NULL)
      { epswr_label(eps, lab, "Lg", x, y, 0, TRUE, hAlign, vAlign, TRUE, FALSE); }
  }
  
void hedge_draw_bezier_eval(double t, double z0, double z1, double z2, double z3, double *z_P, double *dz_P)
  {
    double s = 1.0-t;
    
    double z01 = s*z0 + t*z1; double dz01 = z1 - z0;
    double z12 = s*z1 + t*z2; double dz12 = z2 - z1;
    double z23 = s*z2 + t*z3; double dz23 = z3 - z2;
    
    double z012 = s*z01 + t*z12; double dz012 = z12 - z01 + s*dz01 + t*dz12;
    double z123 = s*z12 + t*z23; double dz123 = z23 - z12 + s*dz12 + t*dz23;

    double z0123 = s*z012 + t*z123; double dz0123 = z123 - z012 + s*dz012 + t*dz123;

    (*z_P) = z0123;
    (*dz_P) = dz0123;
  }


void hedge_draw_choose_lab_align(r2_t *dp, double *hAlign_P, double *vAlign_P);
  /* Chooses the parameters {hAlign} and {vAlign} for {epswr_label}
    based on the direction of the displacement {dp} from the labebeld
    point. The {displacement {dp} must be in the world coordinate
    system, not the local tangent system. */

void hedge_draw_choose_lab_align(r2_t *dp, double *hAlign_P, double *vAlign_P)
  { 
    (*hAlign_P) = (dp->c[0] > 0 ? 0.0 : (dp->c[0] < 0 ? 1.0 : 0.5));
    (*vAlign_P) = (dp->c[1] > 0 ? 0.0 : (dp->c[1] < 0 ? 1.0 : 0.5));
  }

    double hAlign, vAlign;
    hedge_draw_choose_lab_align(&dsp, &hAlign, &vAlign);
    fprintf(stderr, "  align = ( %7.2f, %7.2f )\n", hAlign, vAlign);

    double hAlign, vAlign;
    hedge_draw_choose_lab_align(&dsp, &hAlign, &vAlign);
    fprintf(stderr, "  align = ( %7.2f, %7.2f )\n", hAlign, vAlign);

    double hAlign, vAlign;
    hedge_draw_choose_lab_align(&dp, &hAlign, &vAlign);
    fprintf(stderr, "  align = ( %7.2f, %7.2f )\n", hAlign, vAlign);