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)
34 for (int i = 0; i < arr_p->size (); i++)
35 (*arr_p)[i][a] = - (*arr_p)[i][a];
39 rotate (Array<Offset>* arr_p, Real phi)
41 Offset rot (complex_exp (Offset (0, phi)));
42 for (int i = 0; i < arr_p->size (); i++)
43 (*arr_p)[i] = complex_multiply (rot, (*arr_p)[i]);
47 translate (Array<Offset>* arr_p, Offset o)
49 for (int i = 0; i < arr_p->size (); i++)
55 Formula of the bezier 3-spline
57 sum_{j=0}^3 (3 over j) z_j (1-t)^(3-j) t^j
61 Bezier::get_other_coordinate (Axis a, Real x) const
63 Axis other = Axis ((a +1)%NO_AXES);
64 Array<Real> ts = solve_point (a, x);
66 Offset c = curve_point (ts[0]);
67 assert (fabs (c[a] - x) < 1e-8);
74 Bezier::curve_point (Real t)const
77 Real one_min_tj = (1-t)*(1-t)*(1-t);
80 for (int j=0 ; j < 4; j++)
82 o += control_[j] * binomial_coefficient (3, j)
83 * pow (t,j) * pow (1-t, 3-j);
90 assert (fabs (o[X_AXIS] - polynomial (X_AXIS).eval (t))< 1e-8);
91 assert (fabs (o[Y_AXIS] - polynomial (Y_AXIS).eval (t))< 1e-8);
99 Bezier::polynomial (Axis a)const
102 for (int j=0; j <= 3; j++)
105 * Polynomial::power (j , Polynomial (0,1))*
106 Polynomial::power (3 - j, Polynomial (1,-1))*
107 binomial_coefficient(3, j);
114 Remove all numbers outside [0,1] from SOL
117 filter_solutions (Array<Real> sol)
119 for (int i = sol.size (); i--;)
120 if (sol[i] < 0 || sol[i] >1)
126 find t such that derivative is proportional to DERIV
129 Bezier::solve_derivative (Offset deriv)const
131 Polynomial xp=polynomial (X_AXIS);
132 Polynomial yp=polynomial (Y_AXIS);
136 Polynomial combine = xp * deriv[Y_AXIS] - yp * deriv [X_AXIS];
138 return filter_solutions (combine.solve ());
143 Find t such that curve_point (t)[AX] == COORDINATE
146 Bezier::solve_point (Axis ax, Real coordinate) const
148 Polynomial p(polynomial (ax));
149 p.coefs_[0] -= coordinate;
151 Array<Real> sol (p.solve ());
152 return filter_solutions (sol);
156 Bezier::extent (Axis a)const
158 int o = (a+1)%NO_AXES;
162 Array<Real> sols (solve_derivative (d));
165 for (int i= sols.size (); i--;)
167 Offset o (curve_point (sols[i]));
168 iv.unite (Interval (o[a],o[a]));
174 Bezier::flip (Axis a)
176 for (int i = CONTROL_COUNT; i--;)
177 control_[i][a] = - control_[i][a];
181 Bezier::rotate (Real phi)
183 Offset rot (complex_exp (Offset (0, phi)));
184 for (int i = 0; i < CONTROL_COUNT; i++)
185 control_[i] = complex_multiply (rot, control_[i]);
189 Bezier::translate (Offset o)
191 for (int i = 0; i < CONTROL_COUNT; i++)
196 Bezier::assert_sanity () const
198 for (int i=0; i < CONTROL_COUNT; i++)
199 assert (!isnan (control_[i].length ())
200 && !isinf (control_[i].length ()));
207 for (int i =0; i < CONTROL_COUNT; i++)
208 b2.control_[CONTROL_COUNT-i-1] = control_[i];