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>
14 #include "libc-extension.hh"
16 Real binomial_coefficient_3[] = {
21 binomial_coefficient (Real over, int under)
27 x *= over / Real (under);
36 scale (Array<Offset> *array, Real x, Real y)
38 for (int i = 0; i < array->size (); i++)
40 (*array)[i][X_AXIS] = x * (*array)[i][X_AXIS];
41 (*array)[i][Y_AXIS] = y * (*array)[i][Y_AXIS];
46 rotate (Array<Offset> *array, Real phi)
48 Offset rot (complex_exp (Offset (0, phi)));
49 for (int i = 0; i < array->size (); i++)
50 (*array)[i] = complex_multiply (rot, (*array)[i]);
54 translate (Array<Offset> *array, Offset o)
56 for (int i = 0; i < array->size (); i++)
61 Formula of the bezier 3-spline
63 sum_{j = 0}^3 (3 over j) z_j (1-t)^ (3-j) t^j
66 A is the axis of X coordinate.
70 Bezier::get_other_coordinate (Axis a, Real x) const
72 Axis other = Axis ((a +1)%NO_AXES);
73 Array<Real> ts = solve_point (a, x);
77 programming_error ("no solution found for Bezier intersection");
82 Offset c = curve_point (ts[0]);
83 if (fabs (c[a] - x) > 1e-8)
84 programming_error ("bezier intersection not correct?");
87 return curve_coordinate (ts[0], other);
91 Bezier::curve_coordinate (Real t, Axis a) const
96 for (int i = 1; i < 4; i++)
97 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++)
118 one_min_tj[i] = one_min_tj[i - 1] * (1 - t);
121 for (int j = 0; j < 4; j++)
123 o += control_[j] * binomial_coefficient_3[j]
124 * tj * one_min_tj[3 - j];
130 assert (fabs (o[X_AXIS] - polynomial (X_AXIS).eval (t)) < 1e-8);
131 assert (fabs (o[Y_AXIS] - polynomial (Y_AXIS).eval (t)) < 1e-8);
138 Cache binom(3,j) t^j (1-t)^{3-j}
140 static struct Polynomial bezier_term_cache[4];
141 static bool done_cache_init;
144 init_polynomial_cache ()
146 for (int j = 0; j <= 3; j++)
148 = binomial_coefficient_3[j]
149 * Polynomial::power (j, Polynomial (0, 1))
150 * Polynomial::power (3 - j, Polynomial (1, -1));
151 done_cache_init = true;
155 Bezier::polynomial (Axis a) const
157 if (!done_cache_init)
158 init_polynomial_cache ();
162 for (int j = 0; j <= 3; j++)
164 q = bezier_term_cache[j];
173 Remove all numbers outside [0, 1] from SOL
176 filter_solutions (Array<Real> sol)
178 for (int i = sol.size (); i--;)
179 if (sol[i] < 0 || sol[i] > 1)
185 find t such that derivative is proportional to DERIV
188 Bezier::solve_derivative (Offset deriv) const
190 Polynomial xp = polynomial (X_AXIS);
191 Polynomial yp = polynomial (Y_AXIS);
195 Polynomial combine = xp * deriv[Y_AXIS] - yp * deriv [X_AXIS];
197 return filter_solutions (combine.solve ());
201 Find t such that curve_point (t)[AX] == COORDINATE
204 Bezier::solve_point (Axis ax, Real coordinate) const
206 Polynomial p (polynomial (ax));
207 p.coefs_[0] -= coordinate;
209 Array<Real> sol (p.solve ());
210 return filter_solutions (sol);
214 Compute the bounding box dimensions in direction of A.
217 Bezier::extent (Axis a) const
219 int o = (a + 1)%NO_AXES;
223 Array<Real> sols (solve_derivative (d));
226 for (int i = sols.size (); i--;)
228 Offset o (curve_point (sols[i]));
229 iv.unite (Interval (o[a], o[a]));
238 Bezier::scale (Real x, Real y)
240 for (int i = CONTROL_COUNT; i--;)
242 control_[i][X_AXIS] = x * control_[i][X_AXIS];
243 control_[i][Y_AXIS] = y * control_[i][Y_AXIS];
248 Bezier::rotate (Real phi)
250 Offset rot (complex_exp (Offset (0, phi)));
251 for (int i = 0; i < CONTROL_COUNT; i++)
252 control_[i] = complex_multiply (rot, control_[i]);
256 Bezier::translate (Offset o)
258 for (int i = 0; i < CONTROL_COUNT; i++)
263 Bezier::assert_sanity () const
265 for (int i = 0; i < CONTROL_COUNT; i++)
266 assert (!isnan (control_[i].length ())
267 && !isinf (control_[i].length ()));
274 for (int i = 0; i < CONTROL_COUNT; i++)
275 b2.control_[CONTROL_COUNT - i - 1] = control_[i];