2 spring.cc -- declare Spring
4 source file of the GNU LilyPond music typesetter
6 (c) 2007--2009 Joe Neeman <joeneeman@gmail.com>
15 inverse_stretch_strength_ = 1.0;
16 inverse_compress_strength_ = 1.0;
18 update_blocking_force ();
21 Spring::Spring (Real dist, Real min_dist)
27 set_min_distance (min_dist);
28 set_default_strength ();
29 update_blocking_force ();
33 Spring::update_blocking_force ()
35 if (min_distance_ > distance_)
36 blocking_force_ = (min_distance_ - distance_) / inverse_stretch_strength_;
38 blocking_force_ = (min_distance_ - distance_) / inverse_compress_strength_;
40 if (isnan (blocking_force_) || blocking_force_ == infinity_f)
43 if (blocking_force_ >= 0)
44 inverse_compress_strength_ = 0;
47 /* scale a spring, but in a way that doesn't violate min_distance */
49 Spring::operator*= (Real r)
51 distance_ = max (min_distance_, distance_ * r);
52 inverse_compress_strength_ = max (0.0, distance_ - min_distance_);
53 inverse_stretch_strength_ *= 0.8;
57 Spring::operator> (Spring const &other) const
59 return blocking_force_ > other.blocking_force_;
62 /* merge springs, basically by averaging them, but leave a little headroom
63 above the largest minimum distance so that things don't get too cramped */
65 merge_springs (vector<Spring> const &springs)
67 Real avg_distance = 0;
68 Real min_distance = 0;
70 Real avg_compress = 0;
72 for (vsize i = 0; i < springs.size (); i++)
74 avg_distance += springs[i].distance ();
75 avg_stretch += springs[i].inverse_stretch_strength ();
76 avg_compress += 1 / springs[i].inverse_compress_strength ();
77 min_distance = max (springs[i].min_distance (), min_distance);
80 avg_stretch /= springs.size ();
81 avg_compress /= springs.size ();
82 avg_distance /= springs.size ();
83 avg_distance = max (min_distance + 0.3, avg_distance);
85 Spring ret = Spring (avg_distance, min_distance);
86 ret.set_inverse_stretch_strength (avg_stretch);
87 ret.set_inverse_compress_strength (1 / avg_compress);
93 Spring::set_distance (Real d)
95 if (d < 0 || isinf (d) || isnan (d))
96 programming_error ("insane spring distance requested, ignoring it");
100 update_blocking_force ();
105 Spring::set_min_distance (Real d)
107 if (d < 0 || isinf (d) || isnan (d))
108 programming_error ("insane spring min_distance requested, ignoring it");
112 update_blocking_force ();
117 Spring::ensure_min_distance (Real d)
119 set_min_distance (max (d, min_distance_));
123 Spring::set_inverse_stretch_strength (Real f)
125 if (isinf (f) || isnan (f) || f < 0)
126 programming_error ("insane spring constant");
128 inverse_stretch_strength_ = f;
132 Spring::set_inverse_compress_strength (Real f)
134 if (isinf (f) || isnan (f) || f < 0)
135 programming_error ("insane spring constant");
137 inverse_compress_strength_ = f;
139 update_blocking_force ();
143 Spring::set_blocking_force (Real f)
145 if (isinf (f) || isnan (f))
147 programming_error ("insane blocking force");
151 blocking_force_ = -infinity_f;
152 min_distance_ = length (f);
153 distance_ = max (distance_, min_distance_);
154 update_blocking_force ();
158 Spring::set_default_strength ()
160 inverse_compress_strength_ = (distance_ >= min_distance_) ? distance_ - min_distance_ : 0;
161 inverse_stretch_strength_ = distance_;
165 Spring::length (Real f) const
167 Real force = max (f, blocking_force_);
168 Real inv_k = force < 0.0 ? inverse_compress_strength_ : inverse_stretch_strength_;
172 programming_error ("cruelty to springs");
176 return max (min_distance_, distance_ + force * inv_k);