2 bezier.cc -- implement Bezier and Bezier_bow
4 source file of the GNU LilyPond music typesetter
6 (c) 1998--2005 Jan Nieuwenhuizen <janneke@gnu.org>
13 #include "libc-extension.hh"
15 Real binomial_coefficient_3[] = {1,3 ,3, 1};
18 binomial_coefficient (Real over, int under)
24 x *= over / Real (under);
33 scale (Array<Offset> *array, Real x, Real y)
35 for (int i = 0; i < array->size (); i++)
37 (*array)[i][X_AXIS] = x * (*array)[i][X_AXIS];
38 (*array)[i][Y_AXIS] = y * (*array)[i][Y_AXIS];
43 rotate (Array<Offset> *array, Real phi)
45 Offset rot (complex_exp (Offset (0, phi)));
46 for (int i = 0; i < array->size (); i++)
47 (*array)[i] = complex_multiply (rot, (*array)[i]);
51 translate (Array<Offset> *array, Offset o)
53 for (int i = 0; i < array->size (); i++)
58 Formula of the bezier 3-spline
60 sum_{j = 0}^3 (3 over j) z_j (1-t)^ (3-j) t^j
63 A is the axis of X coordinate.
67 Bezier::get_other_coordinate (Axis a, Real x) const
69 Axis other = Axis ((a +1)%NO_AXES);
70 Array<Real> ts = solve_point (a, x);
74 programming_error ("no solution found for Bezier intersection");
80 Offset c = curve_point (ts[0]);
81 if (fabs (c[a] - x) > 1e-8)
82 programming_error ("bezier intersection not correct?");
85 return curve_coordinate (ts[0], other);
89 Bezier::curve_coordinate (Real t, Axis a) const
94 for (int i = 1; i < 4; i++)
96 one_min_tj[i] = one_min_tj[i-1] * (1-t);
100 for (int j = 0; j < 4; j++)
102 r += control_[j][a] * binomial_coefficient_3[j]
103 * tj * one_min_tj[3-j];
112 Bezier::curve_point (Real t) const
117 for (int i = 1; i < 4; i++)
119 one_min_tj[i] = one_min_tj[i-1] * (1-t);
123 for (int j = 0; j < 4; j++)
125 o += control_[j] * binomial_coefficient_3[j]
126 * tj * one_min_tj[3-j];
132 assert (fabs (o[X_AXIS] - polynomial (X_AXIS).eval (t)) < 1e-8);
133 assert (fabs (o[Y_AXIS] - polynomial (Y_AXIS).eval (t)) < 1e-8);
140 Cache binom(3,j) t^j (1-t)^{3-j}
142 static struct Polynomial bezier_term_cache[4];
143 static bool done_cache_init;
146 init_polynomial_cache ()
148 for (int j = 0; j <= 3; j++)
149 bezier_term_cache[j] =
150 binomial_coefficient_3[j]
151 * Polynomial::power (j, Polynomial (0, 1))
152 * Polynomial::power (3 - j, Polynomial (1, -1));
153 done_cache_init = true;
157 Bezier::polynomial (Axis a) const
159 if (!done_cache_init)
160 init_polynomial_cache ();
164 for (int j = 0; j <= 3; j++)
166 q = bezier_term_cache[j];
175 Remove all numbers outside [0, 1] from SOL
178 filter_solutions (Array<Real> sol)
180 for (int i = sol.size (); i--;)
181 if (sol[i] < 0 || sol[i] > 1)
187 find t such that derivative is proportional to DERIV
190 Bezier::solve_derivative (Offset deriv) const
192 Polynomial xp = polynomial (X_AXIS);
193 Polynomial yp = polynomial (Y_AXIS);
197 Polynomial combine = xp * deriv[Y_AXIS] - yp * deriv [X_AXIS];
199 return filter_solutions (combine.solve ());
203 Find t such that curve_point (t)[AX] == COORDINATE
206 Bezier::solve_point (Axis ax, Real coordinate) const
208 Polynomial p (polynomial (ax));
209 p.coefs_[0] -= coordinate;
211 Array<Real> sol (p.solve ());
212 return filter_solutions (sol);
216 Compute the bounding box dimensions in direction of A.
219 Bezier::extent (Axis a) const
221 int o = (a + 1)%NO_AXES;
225 Array<Real> sols (solve_derivative (d));
228 for (int i = sols.size (); i--;)
230 Offset o (curve_point (sols[i]));
231 iv.unite (Interval (o[a], o[a]));
240 Bezier::scale (Real x, Real y)
242 for (int i = CONTROL_COUNT; i--;)
244 control_[i][X_AXIS] = x * control_[i][X_AXIS];
245 control_[i][Y_AXIS] = y * control_[i][Y_AXIS];
250 Bezier::rotate (Real phi)
252 Offset rot (complex_exp (Offset (0, phi)));
253 for (int i = 0; i < CONTROL_COUNT; i++)
254 control_[i] = complex_multiply (rot, control_[i]);
258 Bezier::translate (Offset o)
260 for (int i = 0; i < CONTROL_COUNT; i++)
265 Bezier::assert_sanity () const
267 for (int i = 0; i < CONTROL_COUNT; i++)
268 assert (!isnan (control_[i].length ())
269 && !isinf (control_[i].length ()));
276 for (int i = 0; i < CONTROL_COUNT; i++)
277 b2.control_[CONTROL_COUNT - i - 1] = control_[i];