1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172

use crate::dynamics::joint::{GenericJoint, GenericJointBuilder, JointAxesMask};
use crate::dynamics::{JointAxis, MotorModel};
use crate::math::{Point, Real};

#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
#[derive(Copy, Clone, Debug, PartialEq)]
#[repr(transparent)]
/// A spring-damper joint, applies a force proportional to the distance between two objects.
///
/// The spring is integrated implicitly, implying that even an undamped spring will be subject to some
/// amount of numerical damping (so it will eventually come to a rest). More solver iterations, or smaller
/// timesteps, will lower the effect of numerical damping, providing a more realistic result.
pub struct SpringJoint {
    /// The underlying joint data.
    pub data: GenericJoint,
}

impl SpringJoint {
    /// Creates a new spring joint limiting the max distance between two bodies.
    ///
    /// The `max_dist` must be strictly greater than 0.0.
    pub fn new(rest_length: Real, stiffness: Real, damping: Real) -> Self {
        let data = GenericJointBuilder::new(JointAxesMask::empty())
            .coupled_axes(JointAxesMask::LIN_AXES)
            .motor_position(JointAxis::LinX, rest_length, stiffness, damping)
            .motor_model(JointAxis::LinX, MotorModel::ForceBased)
            .build();
        Self { data }
    }

    /// The underlying generic joint.
    pub fn data(&self) -> &GenericJoint {
        &self.data
    }

    /// Are contacts between the attached rigid-bodies enabled?
    pub fn contacts_enabled(&self) -> bool {
        self.data.contacts_enabled
    }

    /// Sets whether contacts between the attached rigid-bodies are enabled.
    pub fn set_contacts_enabled(&mut self, enabled: bool) -> &mut Self {
        self.data.set_contacts_enabled(enabled);
        self
    }

    /// The joint’s anchor, expressed in the local-space of the first rigid-body.
    #[must_use]
    pub fn local_anchor1(&self) -> Point<Real> {
        self.data.local_anchor1()
    }

    /// Sets the joint’s anchor, expressed in the local-space of the first rigid-body.
    pub fn set_local_anchor1(&mut self, anchor1: Point<Real>) -> &mut Self {
        self.data.set_local_anchor1(anchor1);
        self
    }

    /// The joint’s anchor, expressed in the local-space of the second rigid-body.
    #[must_use]
    pub fn local_anchor2(&self) -> Point<Real> {
        self.data.local_anchor2()
    }

    /// Sets the joint’s anchor, expressed in the local-space of the second rigid-body.
    pub fn set_local_anchor2(&mut self, anchor2: Point<Real>) -> &mut Self {
        self.data.set_local_anchor2(anchor2);
        self
    }

    /// Set the spring model used by this joint to reach the desired target velocity and position.
    ///
    /// Setting this to `MotorModel::ForceBased` (which is the default value for this joint) makes the spring constants
    /// (stiffness and damping) parameter understood as in the regular spring-mass-damper system. With
    /// `MotorModel::AccelerationBased`, the spring constants will be automatically scaled by the attached masses,
    /// making the spring more mass-independent.
    pub fn set_spring_model(&mut self, model: MotorModel) -> &mut Self {
        self.data.set_motor_model(JointAxis::LinX, model);
        self
    }

    // /// The maximum distance allowed between the attached objects.
    // #[must_use]
    // pub fn rest_length(&self) -> Option<Real> {
    //     self.data.limits(JointAxis::X).map(|l| l.max)
    // }
    //
    // /// Sets the maximum allowed distance between the attached objects.
    // ///
    // /// The `max_dist` must be strictly greater than 0.0.
    // pub fn set_rest_length(&mut self, max_dist: Real) -> &mut Self {
    //     self.data.set_limits(JointAxis::X, [0.0, max_dist]);
    //     self
    // }
}

impl From<SpringJoint> for GenericJoint {
    fn from(val: SpringJoint) -> GenericJoint {
        val.data
    }
}

/// A [SpringJoint] joint using the builder pattern.
///
/// This builds a spring-damper joint which applies a force proportional to the distance between two objects.
/// See the documentation of [SpringJoint] for more information on its behavior.
#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
#[derive(Copy, Clone, Debug, PartialEq)]
pub struct SpringJointBuilder(pub SpringJoint);

impl SpringJointBuilder {
    /// Creates a new builder for spring joints.
    ///
    /// This axis is expressed in the local-space of both rigid-bodies.
    pub fn new(rest_length: Real, stiffness: Real, damping: Real) -> Self {
        Self(SpringJoint::new(rest_length, stiffness, damping))
    }

    /// Sets whether contacts between the attached rigid-bodies are enabled.
    #[must_use]
    pub fn contacts_enabled(mut self, enabled: bool) -> Self {
        self.0.set_contacts_enabled(enabled);
        self
    }

    /// Sets the joint’s anchor, expressed in the local-space of the first rigid-body.
    #[must_use]
    pub fn local_anchor1(mut self, anchor1: Point<Real>) -> Self {
        self.0.set_local_anchor1(anchor1);
        self
    }

    /// Sets the joint’s anchor, expressed in the local-space of the second rigid-body.
    #[must_use]
    pub fn local_anchor2(mut self, anchor2: Point<Real>) -> Self {
        self.0.set_local_anchor2(anchor2);
        self
    }

    /// Set the spring used by this joint to reach the desired target velocity and position.
    ///
    /// Setting this to `MotorModel::ForceBased` (which is the default value for this joint) makes the spring constants
    /// (stiffness and damping) parameter understood as in the regular spring-mass-damper system. With
    /// `MotorModel::AccelerationBased`, the spring constants will be automatically scaled by the attached masses,
    /// making the spring more mass-independent.
    #[must_use]
    pub fn spring_model(mut self, model: MotorModel) -> Self {
        self.0.set_spring_model(model);
        self
    }

    // /// Sets the maximum allowed distance between the attached bodies.
    // ///
    // /// The `max_dist` must be strictly greater than 0.0.
    // #[must_use]
    // pub fn max_distance(mut self, max_dist: Real) -> Self {
    //     self.0.set_max_distance(max_dist);
    //     self
    // }

    /// Builds the spring joint.
    #[must_use]
    pub fn build(self) -> SpringJoint {
        self.0
    }
}

impl From<SpringJointBuilder> for GenericJoint {
    fn from(val: SpringJointBuilder) -> GenericJoint {
        val.0.into()
    }
}