rapier2d 0.7.1

2-dimensional physics engine in Rust.
Documentation 
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
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260

use super::{
    AnyVelocityConstraint, DeltaVel, VelocityGroundConstraintElement,
    VelocityGroundConstraintNormalPart,
};
use crate::math::{Real, Vector, DIM, MAX_MANIFOLD_POINTS};
#[cfg(feature = "dim2")]
use crate::utils::WBasis;
use crate::utils::{WAngularInertia, WCross, WDot};

use crate::dynamics::{IntegrationParameters, RigidBodySet};
use crate::geometry::{ContactManifold, ContactManifoldIndex};

#[derive(Copy, Clone, Debug)]
pub(crate) struct VelocityGroundConstraint {
    pub mj_lambda2: usize,
    pub dir1: Vector<Real>, // Non-penetration force direction for the first body.
    #[cfg(feature = "dim3")]
    pub tangent1: Vector<Real>, // One of the friction force directions.
    pub im2: Real,
    pub limit: Real,
    pub elements: [VelocityGroundConstraintElement<Real>; MAX_MANIFOLD_POINTS],

    #[cfg(feature = "dim3")]
    pub tangent_rot1: na::UnitComplex<Real>, // Orientation of the tangent basis wrt. the reference basis.
    pub manifold_id: ContactManifoldIndex,
    pub manifold_contact_id: [u8; MAX_MANIFOLD_POINTS],
    pub num_contacts: u8,
}

impl VelocityGroundConstraint {
    pub fn generate(
        params: &IntegrationParameters,
        manifold_id: ContactManifoldIndex,
        manifold: &ContactManifold,
        bodies: &RigidBodySet,
        out_constraints: &mut Vec<AnyVelocityConstraint>,
        push: bool,
    ) {
        let inv_dt = params.inv_dt();
        let velocity_based_erp_inv_dt = params.velocity_based_erp_inv_dt();

        let mut rb1 = &bodies[manifold.data.body_pair.body1];
        let mut rb2 = &bodies[manifold.data.body_pair.body2];
        let flipped = manifold.data.relative_dominance < 0;

        let (force_dir1, flipped_multiplier) = if flipped {
            std::mem::swap(&mut rb1, &mut rb2);
            (manifold.data.normal, -1.0)
        } else {
            (-manifold.data.normal, 1.0)
        };

        #[cfg(feature = "dim2")]
        let tangents1 = force_dir1.orthonormal_basis();
        #[cfg(feature = "dim3")]
        let (tangents1, tangent_rot1) =
            super::compute_tangent_contact_directions(&force_dir1, &rb1.linvel, &rb2.linvel);

        let mj_lambda2 = rb2.active_set_offset;
        let warmstart_coeff = manifold.data.warmstart_multiplier * params.warmstart_coeff;

        for (_l, manifold_points) in manifold
            .data
            .solver_contacts
            .chunks(MAX_MANIFOLD_POINTS)
            .enumerate()
        {
            #[cfg(not(target_arch = "wasm32"))]
            let mut constraint = VelocityGroundConstraint {
                dir1: force_dir1,
                #[cfg(feature = "dim3")]
                tangent1: tangents1[0],
                #[cfg(feature = "dim3")]
                tangent_rot1,
                elements: [VelocityGroundConstraintElement::zero(); MAX_MANIFOLD_POINTS],
                im2: rb2.effective_inv_mass,
                limit: 0.0,
                mj_lambda2,
                manifold_id,
                manifold_contact_id: [0; MAX_MANIFOLD_POINTS],
                num_contacts: manifold_points.len() as u8,
            };

            // TODO: this is a WIP optimization for WASM platforms.
            // For some reasons, the compiler does not inline the `Vec::push` method
            // in this method. This generates two memset and one memcpy which are both very
            // expansive.
            // This would likely be solved by some kind of "placement-push" (like emplace in C++).
            // In the mean time, a workaround is to "push" using `.resize_with` and `::uninit()` to
            // avoid spurious copying.
            // Is this optimization beneficial when targeting non-WASM platforms?
            //
            // NOTE: joints have the same problem, but it is not easy to refactor the code that way
            // for the moment.
            #[cfg(target_arch = "wasm32")]
            let constraint = if push {
                let new_len = out_constraints.len() + 1;
                unsafe {
                    out_constraints.resize_with(new_len, || {
                        AnyVelocityConstraint::NongroupedGround(
                            std::mem::MaybeUninit::uninit().assume_init(),
                        )
                    });
                }
                out_constraints
                    .last_mut()
                    .unwrap()
                    .as_nongrouped_ground_mut()
                    .unwrap()
            } else {
                unreachable!(); // We don't have parallelization on WASM yet, so this is unreachable.
            };

            #[cfg(target_arch = "wasm32")]
            {
                constraint.dir1 = force_dir1;
                #[cfg(feature = "dim3")]
                {
                    constraint.tangent1 = tangents1[0];
                    constraint.tangent_rot1 = tangent_rot1;
                }
                constraint.im2 = rb2.effective_inv_mass;
                constraint.limit = 0.0;
                constraint.mj_lambda2 = mj_lambda2;
                constraint.manifold_id = manifold_id;
                constraint.manifold_contact_id = [0; MAX_MANIFOLD_POINTS];
                constraint.num_contacts = manifold_points.len() as u8;
            }

            for k in 0..manifold_points.len() {
                let manifold_point = &manifold_points[k];
                let dp2 = manifold_point.point - rb2.world_com;
                let dp1 = manifold_point.point - rb1.world_com;
                let vel1 = rb1.linvel + rb1.angvel.gcross(dp1);
                let vel2 = rb2.linvel + rb2.angvel.gcross(dp2);
                let warmstart_correction;

                constraint.limit = manifold_point.friction;
                constraint.manifold_contact_id[k] = manifold_point.contact_id;

                // Normal part.
                {
                    let gcross2 = rb2
                        .effective_world_inv_inertia_sqrt
                        .transform_vector(dp2.gcross(-force_dir1));

                    let r = 1.0 / (rb2.effective_inv_mass + gcross2.gdot(gcross2));

                    let is_bouncy = manifold_point.is_bouncy() as u32 as Real;
                    let is_resting = 1.0 - is_bouncy;

                    let mut rhs = (1.0 + is_bouncy * manifold_point.restitution)
                        * (vel1 - vel2).dot(&force_dir1);
                    rhs += manifold_point.dist.max(0.0) * inv_dt;
                    rhs *= is_bouncy + is_resting * params.velocity_solve_fraction;
                    rhs += is_resting * velocity_based_erp_inv_dt * manifold_point.dist.min(0.0);
                    warmstart_correction = (params.warmstart_correction_slope
                        / (rhs - manifold_point.prev_rhs).abs())
                    .min(warmstart_coeff);

                    constraint.elements[k].normal_part = VelocityGroundConstraintNormalPart {
                        gcross2,
                        rhs,
                        impulse: manifold_point.warmstart_impulse * warmstart_correction,
                        r,
                    };
                }

                // Tangent parts.
                {
                    #[cfg(feature = "dim3")]
                    let impulse = tangent_rot1
                        * manifold_points[k].warmstart_tangent_impulse
                        * warmstart_correction;
                    #[cfg(feature = "dim2")]
                    let impulse =
                        [manifold_points[k].warmstart_tangent_impulse * warmstart_correction];
                    constraint.elements[k].tangent_part.impulse = impulse;

                    for j in 0..DIM - 1 {
                        let gcross2 = rb2
                            .effective_world_inv_inertia_sqrt
                            .transform_vector(dp2.gcross(-tangents1[j]));
                        let r = 1.0 / (rb2.effective_inv_mass + gcross2.gdot(gcross2));
                        let rhs = (vel1 - vel2
                            + flipped_multiplier * manifold_point.tangent_velocity)
                            .dot(&tangents1[j]);

                        constraint.elements[k].tangent_part.gcross2[j] = gcross2;
                        constraint.elements[k].tangent_part.rhs[j] = rhs;
                        constraint.elements[k].tangent_part.r[j] = r;
                    }
                }
            }

            #[cfg(not(target_arch = "wasm32"))]
            if push {
                out_constraints.push(AnyVelocityConstraint::NongroupedGround(constraint));
            } else {
                out_constraints[manifold.data.constraint_index + _l] =
                    AnyVelocityConstraint::NongroupedGround(constraint);
            }
        }
    }

    pub fn warmstart(&self, mj_lambdas: &mut [DeltaVel<Real>]) {
        let mut mj_lambda2 = DeltaVel::zero();

        VelocityGroundConstraintElement::warmstart_group(
            &self.elements[..self.num_contacts as usize],
            &self.dir1,
            #[cfg(feature = "dim3")]
            &self.tangent1,
            self.im2,
            &mut mj_lambda2,
        );

        mj_lambdas[self.mj_lambda2 as usize].linear += mj_lambda2.linear;
        mj_lambdas[self.mj_lambda2 as usize].angular += mj_lambda2.angular;
    }

    pub fn solve(&mut self, mj_lambdas: &mut [DeltaVel<Real>]) {
        let mut mj_lambda2 = mj_lambdas[self.mj_lambda2 as usize];

        VelocityGroundConstraintElement::solve_group(
            &mut self.elements[..self.num_contacts as usize],
            &self.dir1,
            #[cfg(feature = "dim3")]
            &self.tangent1,
            self.im2,
            self.limit,
            &mut mj_lambda2,
        );

        mj_lambdas[self.mj_lambda2 as usize] = mj_lambda2;
    }

    // FIXME: duplicated code. This is exactly the same as in the non-ground velocity constraint.
    pub fn writeback_impulses(&self, manifolds_all: &mut [&mut ContactManifold]) {
        let manifold = &mut manifolds_all[self.manifold_id];

        for k in 0..self.num_contacts as usize {
            let contact_id = self.manifold_contact_id[k];
            let active_contact = &mut manifold.points[contact_id as usize];
            active_contact.data.impulse = self.elements[k].normal_part.impulse;
            active_contact.data.rhs = self.elements[k].normal_part.rhs;

            #[cfg(feature = "dim2")]
            {
                active_contact.data.tangent_impulse = self.elements[k].tangent_part.impulse[0];
            }
            #[cfg(feature = "dim3")]
            {
                active_contact.data.tangent_impulse = self
                    .tangent_rot1
                    .inverse_transform_vector(&self.elements[k].tangent_part.impulse);
            }
        }
    }
}