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use std::f32;
use std::marker::PhantomData;
use cgmath::{EuclideanSpace, InnerSpace};
use smallvec::SmallVec;
use manifold::*;
use physics::*;
pub trait ConstrainedSet<Index, Constrained, Inspected>
where
Index: Copy
{
fn get(&self, Index) -> (Constrained, Inspected);
fn set(&mut self, Index, Constrained);
}
pub trait Constraint {
type Index: Copy;
type Constrained;
type Inspected;
fn solve<T: ConstrainedSet<Self::Index, Self::Constrained, Self::Inspected>>(&mut self, &mut T);
}
pub struct Solver<C: Constraint> {
constraints: SmallVec<[C; 10]>,
}
impl<C: Constraint> Solver<C> {
pub fn new() -> Self {
Solver {
constraints: SmallVec::new(),
}
}
pub fn add_constraint(&mut self, constraint: C) {
self.constraints.push(constraint);
}
pub fn solve<T: ConstrainedSet<C::Index, C::Constrained, C::Inspected>>(&mut self, cs: &mut T, iters: usize) {
for _ in 0..iters {
for constraint in self.constraints.iter_mut() {
constraint.solve(cs);
}
}
}
}
pub struct ContactConstraint<Index, Params = DefaultContactConstraintParams>
where
Index: Copy,
Params: ContactConstraintParams
{
obj_a: Index,
obj_b: Index,
manifold: Manifold,
friction: f32,
states: SmallVec<[ContactState; 4]>,
params: PhantomData<Params>,
}
impl<Index, Params> ContactConstraint<Index, Params>
where
Index: Copy,
Params: ContactConstraintParams
{
pub fn new<T: ConstrainedSet<Index, Velocity, RigidBodyInfo>>(pool: &T, obj_a: Index, obj_b: Index, manifold: Manifold, dt: f32) -> Self {
let (
Velocity { linear: va, angular: oa },
RigidBodyInfo {
x: xa,
restitution: rest_a,
friction: fric_a,
inv_mass: inv_mass_a,
inv_moment: inv_moment_a
}
) = pool.get(obj_a);
let (
Velocity { linear: vb, angular: ob },
RigidBodyInfo {
x: xb,
restitution: rest_b,
friction: fric_b,
inv_mass: inv_mass_b,
inv_moment: inv_moment_b
}
) = pool.get(obj_b);
let restitution = rest_a.max(rest_b);
let friction = (fric_a * fric_b).sqrt();
let mut states = SmallVec::with_capacity(manifold.contacts.len());
for &(local_a, local_b) in manifold.contacts.iter() {
let ra = local_a.to_vec();
let rb = local_b.to_vec();
let ca = ra + xa.to_vec();
let cb = rb + xb.to_vec();
let ra_cn = ra.cross(manifold.normal);
let rb_cn = rb.cross(manifold.normal);
let pen = (cb - ca).dot(manifold.normal);
let dv = vb + ob.cross(rb) - va - oa.cross(ra);
let rel_v = dv.dot(manifold.normal);
let bias = -Params::BAUMGARTE / dt * if pen > 0.0 {
0.0
} else {
pen + Params::PENETRATION_SLOP
} + if rel_v < -1.0 {
-restitution * rel_v
} else {
0.0
};
let normal_mass = 1.0 /
(inv_mass_a + ra_cn.dot(inv_moment_a * ra_cn)
+ inv_mass_b + rb_cn.dot(inv_moment_b * rb_cn));
let tangent_mass = [
{
let ra_ct = ra.cross(manifold.tangent_vector[0]);
let rb_ct = rb.cross(manifold.tangent_vector[0]);
1.0 / (inv_mass_a + ra_ct.dot(inv_moment_a * ra_ct)
+ inv_mass_b + rb_ct.dot(inv_moment_b * rb_ct))
},
{
let ra_ct = ra.cross(manifold.tangent_vector[1]);
let rb_ct = rb.cross(manifold.tangent_vector[1]);
1.0 / (inv_mass_a + ra_ct.dot(inv_moment_a * ra_ct)
+ inv_mass_b + rb_ct.dot(inv_moment_b * rb_ct))
}
];
states.push(ContactState {
bias,
normal_mass,
normal_impulse: 0.0,
tangent_mass,
tangent_impulse: [ 0.0, 0.0 ]
})
}
ContactConstraint {
obj_a,
obj_b,
manifold,
friction,
states,
params: PhantomData,
}
}
}
impl<Index, Params> Constraint for ContactConstraint<Index, Params>
where
Index: Copy,
Params: ContactConstraintParams
{
type Index = Index;
type Constrained = Velocity;
type Inspected = RigidBodyInfo;
fn solve<T: ConstrainedSet<Index, Velocity, RigidBodyInfo>>(&mut self, pool: &mut T) {
let (
Velocity{ linear: mut va, angular: mut oa },
RigidBodyInfo{ inv_mass: inv_mass_a, inv_moment: inv_moment_a, .. }
) = pool.get(self.obj_a);
let (
Velocity{ linear: mut vb, angular: mut ob },
RigidBodyInfo{ inv_mass: inv_mass_b, inv_moment: inv_moment_b, .. }
) = pool.get(self.obj_b);
for (i, ref mut contact_state) in self.states.iter_mut().enumerate() {
let (local_a, local_b) = self.manifold.contacts[i];
let (ra, rb) = (local_a.to_vec(), local_b.to_vec());
let dv = vb + ob.cross(rb) - va - oa.cross(ra);
for i in 0..2 {
let lambda = -dv.dot(self.manifold.tangent_vector[i])
* contact_state.tangent_mass[i];
let max_lambda = self.friction * contact_state.normal_impulse;
let prev_impulse = contact_state.tangent_impulse[i];
contact_state.tangent_impulse[i] =
clamp(-max_lambda, max_lambda, prev_impulse + lambda);
let impulse = self.manifold.tangent_vector[i] * lambda;
va -= impulse * inv_mass_a;
oa -= inv_moment_a * ra.cross(impulse);
vb += impulse * inv_mass_b;
ob += inv_moment_b * rb.cross(impulse);
}
let dv = vb + ob.cross(rb) - va - oa.cross(ra);
let vn = dv.dot(self.manifold.normal);
let lambda = contact_state.normal_mass * (-vn + contact_state.bias);
let prev_impulse = contact_state.normal_impulse;
contact_state.normal_impulse = (prev_impulse + lambda).max(0.0);
let lambda = contact_state.normal_impulse - prev_impulse;
let impulse = self.manifold.normal * lambda;
va -= impulse * inv_mass_a;
oa -= inv_moment_a * ra.cross(impulse);
vb += impulse * inv_mass_b;
ob += inv_moment_b * rb.cross(impulse);
}
pool.set(self.obj_a, Velocity{ linear: va, angular: oa });
pool.set(self.obj_b, Velocity{ linear: vb, angular: ob });
}
}
struct ContactState {
bias: f32,
normal_mass: f32,
normal_impulse: f32,
tangent_mass: [f32; 2],
tangent_impulse: [f32; 2],
}
pub trait ContactConstraintParams {
const PENETRATION_SLOP: f32;
const BAUMGARTE: f32;
}
pub struct DefaultContactConstraintParams {}
impl ContactConstraintParams for DefaultContactConstraintParams {
const PENETRATION_SLOP: f32 = 0.05;
const BAUMGARTE: f32 = 0.2;
}
fn clamp(n: f32, min: f32, max: f32) -> f32 {
if n < min {
min
} else if n > max {
max
} else {
n
}
}