2 bezier.cc -- implement Bezier and Bezier_bow
4 source file of the GNU LilyPond music typesetter
6 (c) 1998--2000 Jan Nieuwenhuizen <janneke@gnu.org>
14 #include "polynomial.hh"
17 binomial_coefficient (Real over , int under)
23 x *= over / Real (under);
32 flip (Array<Offset>* arr_p, Axis a)
35 // for (int i = c.size (); i--;)
36 for (int i = 0; i < arr_p->size (); i++)
37 (*arr_p)[i][a] = - (*arr_p)[i][a];
41 rotate (Array<Offset>* arr_p, Real phi)
43 Offset rot (complex_exp (Offset (0, phi)));
44 for (int i = 0; i < arr_p->size (); i++)
45 (*arr_p)[i] = complex_multiply (rot, (*arr_p)[i]);
49 translate (Array<Offset>* arr_p, Offset o)
51 for (int i = 0; i < arr_p->size (); i++)
57 Formula of the bezier 3-spline
59 sum_{j=0}^3 (3 over j) z_j (1-t)^(3-j) t^j
63 Bezier::get_other_coordinate (Axis a, Real x) const
65 Axis other = Axis ((a +1)%NO_AXES);
66 Array<Real> ts = solve_point (a, x);
68 Offset c = curve_point (ts[0]);
69 assert (fabs (c[a] - x) < 1e-8);
76 Bezier::curve_point (Real t)const
79 Real one_min_tj = (1-t)*(1-t)*(1-t);
82 for (int j=0 ; j < 4; j++)
84 o += control_[j] * binomial_coefficient (3, j)
85 * pow (t,j) * pow (1-t, 3-j);
92 assert (fabs (o[X_AXIS] - polynomial (X_AXIS).eval (t))< 1e-8);
93 assert (fabs (o[Y_AXIS] - polynomial (Y_AXIS).eval (t))< 1e-8);
101 Bezier::polynomial (Axis a)const
104 for (int j=0; j <= 3; j++)
107 * Polynomial::power (j , Polynomial (0,1))*
108 Polynomial::power (3 - j, Polynomial (1,-1))*
109 binomial_coefficient(3, j);
116 Remove all numbers outside [0,1] from SOL
119 filter_solutions (Array<Real> sol)
121 for (int i = sol.size (); i--;)
122 if (sol[i] < 0 || sol[i] >1)
128 find t such that derivative is proportional to DERIV
131 Bezier::solve_derivative (Offset deriv)const
133 Polynomial xp=polynomial (X_AXIS);
134 Polynomial yp=polynomial (Y_AXIS);
138 Polynomial combine = xp * deriv[Y_AXIS] - yp * deriv [X_AXIS];
140 return filter_solutions (combine.solve ());
145 Find t such that curve_point (t)[AX] == COORDINATE
148 Bezier::solve_point (Axis ax, Real coordinate) const
150 Polynomial p(polynomial (ax));
151 p.coefs_[0] -= coordinate;
153 Array<Real> sol (p.solve ());
154 return filter_solutions (sol);
158 Bezier::extent (Axis a)const
160 int o = (a+1)%NO_AXES;
164 Array<Real> sols (solve_derivative (d));
167 for (int i= sols.size (); i--;)
169 Offset o (curve_point (sols[i]));
170 iv.unite (Interval (o[a],o[a]));
176 Bezier::flip (Axis a)
178 for (int i = CONTROL_COUNT; i--;)
179 control_[i][a] = - control_[i][a];
183 Bezier::rotate (Real phi)
185 Offset rot (complex_exp (Offset (0, phi)));
186 for (int i = 0; i < CONTROL_COUNT; i++)
187 control_[i] = complex_multiply (rot, control_[i]);
191 Bezier::translate (Offset o)
193 for (int i = 0; i < CONTROL_COUNT; i++)
198 Bezier::assert_sanity () const
200 for (int i=0; i < CONTROL_COUNT; i++)
201 assert (!isnan (control_[i].length ())
202 && !isinf (control_[i].length ()));
209 for (int i =0; i < CONTROL_COUNT; i++)
210 b2.control_[CONTROL_COUNT-i-1] = control_[i];