2 bezier.cc -- implement Bezier and Bezier_bow
4 source file of the GNU LilyPond music typesetter
6 (c) 1998--2002 Jan Nieuwenhuizen <janneke@gnu.org>
13 #include "libc-extension.hh"
15 #include "polynomial.hh"
18 binomial_coefficient (Real over , int under)
24 x *= over / Real (under);
33 scale (Array<Offset>* arr_p, Real x , Real y)
35 for (int i = 0; i < arr_p->size (); i++)
37 (*arr_p)[i][X_AXIS] = x* (*arr_p)[i][X_AXIS];
38 (*arr_p)[i][Y_AXIS] = y* (*arr_p)[i][Y_AXIS];
43 rotate (Array<Offset>* arr_p, Real phi)
45 Offset rot (complex_exp (Offset (0, phi)));
46 for (int i = 0; i < arr_p->size (); i++)
47 (*arr_p)[i] = complex_multiply (rot, (*arr_p)[i]);
51 translate (Array<Offset>* arr_p, Offset o)
53 for (int i = 0; i < arr_p->size (); i++)
59 Formula of the bezier 3-spline
61 sum_{j=0}^3 (3 over j) z_j (1-t)^ (3-j) t^j
65 Bezier::get_other_coordinate (Axis a, Real x) const
67 Axis other = Axis ((a +1)%NO_AXES);
68 Array<Real> ts = solve_point (a, x);
72 programming_error ("No solution found for Bezier intersection.");
76 Offset c = curve_point (ts[0]);
77 assert (fabs (c[a] - x) < 1e-8);
84 Bezier::curve_point (Real t)const
87 Real one_min_tj = (1-t)* (1-t)* (1-t);
90 for (int j=0 ; j < 4; j++)
92 o += control_[j] * binomial_coefficient (3, j)
93 * pow (t,j) * pow (1-t, 3-j);
101 assert (fabs (o[X_AXIS] - polynomial (X_AXIS).eval (t))< 1e-8);
102 assert (fabs (o[Y_AXIS] - polynomial (Y_AXIS).eval (t))< 1e-8);
110 Bezier::polynomial (Axis a)const
113 for (int j=0; j <= 3; j++)
116 * Polynomial::power (j , Polynomial (0,1))*
117 Polynomial::power (3 - j, Polynomial (1,-1))*
118 binomial_coefficient (3, j);
125 Remove all numbers outside [0,1] from SOL
128 filter_solutions (Array<Real> sol)
130 for (int i = sol.size (); i--;)
131 if (sol[i] < 0 || sol[i] >1)
137 find t such that derivative is proportional to DERIV
140 Bezier::solve_derivative (Offset deriv)const
142 Polynomial xp=polynomial (X_AXIS);
143 Polynomial yp=polynomial (Y_AXIS);
147 Polynomial combine = xp * deriv[Y_AXIS] - yp * deriv [X_AXIS];
149 return filter_solutions (combine.solve ());
154 Find t such that curve_point (t)[AX] == COORDINATE
157 Bezier::solve_point (Axis ax, Real coordinate) const
159 Polynomial p (polynomial (ax));
160 p.coefs_[0] -= coordinate;
162 Array<Real> sol (p.solve ());
163 return filter_solutions (sol);
167 Compute the bounding box dimensions in direction of A.
170 Bezier::extent (Axis a)const
172 int o = (a+1)%NO_AXES;
176 Array<Real> sols (solve_derivative (d));
179 for (int i= sols.size (); i--;)
181 Offset o (curve_point (sols[i]));
182 iv.unite (Interval (o[a],o[a]));
192 Bezier::scale (Real x, Real y)
194 for (int i = CONTROL_COUNT; i--;)
196 control_[i][X_AXIS] = x * control_[i][X_AXIS];
197 control_[i][Y_AXIS] = y * control_[i][Y_AXIS];
202 Bezier::rotate (Real phi)
204 Offset rot (complex_exp (Offset (0, phi)));
205 for (int i = 0; i < CONTROL_COUNT; i++)
206 control_[i] = complex_multiply (rot, control_[i]);
210 Bezier::translate (Offset o)
212 for (int i = 0; i < CONTROL_COUNT; i++)
217 Bezier::assert_sanity () const
219 for (int i=0; i < CONTROL_COUNT; i++)
220 assert (!isnan (control_[i].length ())
221 && !isinf (control_[i].length ()));
228 for (int i =0; i < CONTROL_COUNT; i++)
229 b2.control_[CONTROL_COUNT-i-1] = control_[i];