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zfergus merged 3 commits into from
Mar 1, 2026
Merged

Refactor Nonlinear CCD Implementation into a Class #218

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918b54d
Refactor Nonlinear CCD Implementation and Update Tests
zfergus Mar 1, 2026
302eba6
Apply suggestions from code review
zfergus Mar 1, 2026
a8b5686
Make NonlinearCCD::point_triangle_ccd virtual
zfergus Mar 1, 2026
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6 changes: 3 additions & 3 deletions docs/source/tutorials/nonlinear_ccd.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -199,13 +199,13 @@ The following code snippet shows an example of how to use interval arithmetic to

.. code-block:: cpp

#include <ipc/utils/interval.hpp>
#include <ipc/math/interval.hpp>

using namespace ipc;

Vector2I position(
const VectorMax3d& center,
const VectorMax3d& point,
Eigen::ConstRef<VectorMax3d> center,
Eigen::ConstRef<VectorMax3d> point,
const double omega,
const Interval& t)
{
Expand Down
325 changes: 151 additions & 174 deletions python/src/ccd/nonlinear_ccd.cpp
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78 changes: 55 additions & 23 deletions python/tests/test_ccd.py
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Original file line number Diff line number Diff line change
@@ -1,8 +1,6 @@
import numpy as np

from find_ipctk import ipctk
from ipctk.filib import Interval

from utils import load_mesh


Expand All @@ -28,16 +26,44 @@ class DumbNarrowPhaseCCD(ipctk.NarrowPhaseCCD):
def __init__(self):
ipctk.NarrowPhaseCCD.__init__(self)

def point_point_ccd(self, p0_t0, p1_t0, p0_t1, p1_t1, min_distance=0.0, tmax=1.0):
def point_point_ccd(
self, p0_t0, p1_t0, p0_t1, p1_t1, min_distance=0.0, tmax=1.0
):
return True, 0.0

def point_edge_ccd(self, p_t0, e0_t0, e1_t0, p_t1, e0_t1, e1_t1, min_distance=0.0, tmax=1.0):
def point_edge_ccd(
self, p_t0, e0_t0, e1_t0, p_t1, e0_t1, e1_t1, min_distance=0.0, tmax=1.0
):
return True, 0.0

def point_triangle_ccd(self, p_t0, t0_t0, t1_t0, t2_t0, p_t1, t0_t1, t1_t1, t2_t1, min_distance=0.0, tmax=1.0):
def point_triangle_ccd(
self,
p_t0,
t0_t0,
t1_t0,
t2_t0,
p_t1,
t0_t1,
t1_t1,
t2_t1,
min_distance=0.0,
tmax=1.0,
):
return True, 0.0

def edge_edge_ccd(self, ea0_t0, ea1_t0, eb0_t0, eb1_t0, ea0_t1, ea1_t1, eb0_t1, eb1_t1, min_distance=0.0, tmax=1.0):
def edge_edge_ccd(
self,
ea0_t0,
ea1_t0,
eb0_t0,
eb1_t0,
ea0_t1,
ea1_t1,
eb0_t1,
eb1_t1,
min_distance=0.0,
tmax=1.0,
):
return True, 0.0

V0, E, F = load_mesh("two-cubes-close.ply")
Expand All @@ -48,10 +74,12 @@ def edge_edge_ccd(self, ea0_t0, ea1_t0, eb0_t0, eb1_t0, ea0_t1, ea1_t1, eb0_t1,
ipctk.set_num_threads(1)

assert not ipctk.is_step_collision_free(
mesh, V0, V1, narrow_phase_ccd=DumbNarrowPhaseCCD())
mesh, V0, V1, narrow_phase_ccd=DumbNarrowPhaseCCD()
)

toi = ipctk.compute_collision_free_stepsize(
mesh, V0, V1, narrow_phase_ccd=DumbNarrowPhaseCCD())
mesh, V0, V1, narrow_phase_ccd=DumbNarrowPhaseCCD()
)
assert 0 <= toi <= 1


Expand Down Expand Up @@ -90,8 +118,7 @@ def detect_face_face_candidates(self):

assert ipctk.is_step_collision_free(mesh, V0, V1, broad_phase=broad_phase)

toi = ipctk.compute_collision_free_stepsize(
mesh, V0, V1, broad_phase=broad_phase)
toi = ipctk.compute_collision_free_stepsize(mesh, V0, V1, broad_phase=broad_phase)
assert toi == 1

assert not ipctk.has_intersections(mesh, V0, broad_phase=broad_phase)
Expand Down Expand Up @@ -124,7 +151,9 @@ def max_distance_from_linear(self, t0: float, t1: float):
assert p0.max_distance_from_linear(0, 1) == 0
assert p1.max_distance_from_linear(0, 1) == 0

is_colliding, toi = ipctk.point_point_nonlinear_ccd(p0, p1)
ccd = ipctk.NonlinearCCD()

is_colliding, toi = ccd.point_point_ccd(p0, p1)

assert is_colliding
assert 0 < toi < 1
Expand All @@ -145,15 +174,17 @@ def max_distance_from_linear(self, t0: float, t1: float):
# p0 = IntervalLinearTrajectory(np.array([-1, 0, 0]), np.array([1, 0, 0]))
# p1 = IntervalLinearTrajectory(np.array([0, -1, 0]), np.array([0, 1, 0]))

# is_colliding, toi = ipctk.point_point_nonlinear_ccd(p0, p1)
# is_colliding, toi = ccd.point_point_ccd(p0, p1)

# assert is_colliding
# assert 0 < toi < 1
# assert np.abs(toi - 0.5) < 1e-2

# BEGIN_RIGID_2D_TRAJECTORY
class Rigid2DTrajectory(ipctk.NonlinearTrajectory):
def __init__(self, position, translation, delta_translation, rotation, delta_rotation):
def __init__(
self, position, translation, delta_translation, rotation, delta_rotation
):
ipctk.NonlinearTrajectory.__init__(self)
self.position = position
self.translation = translation
Expand All @@ -164,9 +195,11 @@ def __init__(self, position, translation, delta_translation, rotation, delta_rot
# BEGIN_RIGID_2D_CALL
def __call__(self, t):
theta = self.rotation + t * self.delta_rotation
R = np.array([[np.cos(theta), -np.sin(theta)],
[np.sin(theta), np.cos(theta)]])
R = np.array(
[[np.cos(theta), -np.sin(theta)], [np.sin(theta), np.cos(theta)]]
)
return R @ self.position + self.translation + t * self.delta_translation

# END_RIGID_2D_CALL

# BEGIN_RIGID_2D_MAX_DISTANCE_FROM_LINEAR
Expand All @@ -177,20 +210,19 @@ def max_distance_from_linear(self, t0, t1):
p_t0 = self(t0)
p_t1 = self(t1)
return np.linalg.norm(self((t0 + t1) / 2) - ((p_t1 - p_t0) * 0.5 + p_t0))

# END_RIGID_2D_MAX_DISTANCE_FROM_LINEAR

# END_RIGID_2D_TRAJECTORY

# BEGIN_TEST_RIGID_2D_TRAJECTORY
p = Rigid2DTrajectory(
np.array([0, 0.5]), np.zeros(2), np.zeros(2), 0, 0)
e0 = Rigid2DTrajectory(
np.array([-1, 0]), np.zeros(2), np.zeros(2), 0, np.pi)
e1 = Rigid2DTrajectory(
np.array([1, 0]), np.zeros(2), np.zeros(2), 0, np.pi)
p = Rigid2DTrajectory(np.array([0, 0.5]), np.zeros(2), np.zeros(2), 0, 0)
e0 = Rigid2DTrajectory(np.array([-1, 0]), np.zeros(2), np.zeros(2), 0, np.pi)
e1 = Rigid2DTrajectory(np.array([1, 0]), np.zeros(2), np.zeros(2), 0, np.pi)

# increase the conservative_rescaling from 0.8 to 0.9 to get a more accurate estimate
collision, toi = ipctk.point_edge_nonlinear_ccd(
p, e0, e1, conservative_rescaling=0.9)
ccd.conservative_rescaling = 0.9
collision, toi = ccd.point_edge_ccd(p, e0, e1)

assert collision
assert 0.49 <= toi <= 0.5 # conservative estimate
Expand Down
70 changes: 34 additions & 36 deletions src/ipc/ccd/nonlinear_ccd.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,17 @@ double IntervalNonlinearTrajectory::max_distance_from_linear(

// ============================================================================

bool conservative_piecewise_linear_ccd(
NonlinearCCD::NonlinearCCD(
const double _tolerance,
const long _max_iterations,
const double _conservative_rescaling)
: tolerance(_tolerance)
, max_iterations(_max_iterations)
, conservative_rescaling(_conservative_rescaling)
{
}

bool NonlinearCCD::conservative_piecewise_linear_ccd(
const std::function<double(const double)>& distance,
const std::function<double(const double, const double)>&
max_distance_from_linear,
Expand All @@ -62,15 +72,15 @@ bool conservative_piecewise_linear_ccd(
const bool /*no_zero_toi*/,
double& /*toi*/)>& linear_ccd,
double& toi,
const double min_distance,
const double tmax,
const double min_sep_distance,
const double conservative_rescaling)
{
const double distance_t0 = distance(0);
if (check_initial_distance(distance_t0, min_sep_distance, toi)) {
if (check_initial_distance(distance_t0, min_distance, toi)) {
return true;
}
assert(distance_t0 > min_sep_distance);
assert(distance_t0 > min_distance);

double ti0 = 0;
std::stack<double> ts;
Expand Down Expand Up @@ -102,38 +112,38 @@ bool conservative_piecewise_linear_ccd(
return true;
}

double min_distance = max_distance_from_linear(ti0, ti1);
double min_distance_linear = max_distance_from_linear(ti0, ti1);

#ifndef USE_FIXED_PIECES
// Check if the minimum distance is too large and we need to subdivide
// (Large distances cause the slow CCD)
if ((min_distance
if ((min_distance_linear
>= std::min((1 - conservative_rescaling) * distance_ti0, 0.01))
&& (num_subdivisions < MAX_NUM_SUBDIVISIONS || ti0 == 0)) {
logger().trace(
"Subdividing at ti=[{:g}, {:g}] min_distance={:g} distance_ti0={:g}",
ti0, ti1, min_distance, distance_ti0);
ti0, ti1, min_distance_linear, distance_ti0);
ts.push((ti1 + ti0) / 2);
num_subdivisions++;
continue;
}
#endif

min_distance += min_sep_distance;
min_distance_linear += min_distance;

const bool is_impacting =
linear_ccd(ti0, ti1, min_distance, /*no_zero_toi=*/ti0 == 0, toi);
const bool is_impacting = linear_ccd(
ti0, ti1, min_distance_linear, /*no_zero_toi=*/ti0 == 0, toi);

logger().trace(
"Evaluated at ti=[{:g}, {:g}] min_distance={:g} distance_ti0={:g}; result={}{}",
ti0, ti1, min_distance, distance_ti0, is_impacting,
ti0, ti1, min_distance_linear, distance_ti0, is_impacting,
is_impacting ? fmt::format(" toi={:g}", (ti1 - ti0) * toi + ti0)
: "");

if (is_impacting) {
toi = (ti1 - ti0) * toi + ti0;
if (toi == 0) {
// This is impossible because distance_t0 > min_sep_distance
// This is impossible because distance_t0 > min_distance
ts.push((ti1 + ti0) / 2);
num_subdivisions++;
continue;
Expand All @@ -150,15 +160,12 @@ bool conservative_piecewise_linear_ccd(

// ============================================================================

bool point_point_nonlinear_ccd(
bool NonlinearCCD::point_point_ccd(
const NonlinearTrajectory& p0,
const NonlinearTrajectory& p1,
double& toi,
const double tmax,
const double min_distance,
const double tolerance,
const long max_iterations,
const double conservative_rescaling)
const double tmax) const
{
return conservative_piecewise_linear_ccd(
[&](const double t) {
Expand All @@ -184,19 +191,16 @@ bool point_point_nonlinear_ccd(
output_tolerance, // delta_actual
no_zero_toi); // no zero toi
},
toi, tmax, min_distance, conservative_rescaling);
toi, min_distance, tmax, conservative_rescaling);
}

bool point_edge_nonlinear_ccd(
bool NonlinearCCD::point_edge_ccd(
const NonlinearTrajectory& p,
const NonlinearTrajectory& e0,
const NonlinearTrajectory& e1,
double& toi,
const double tmax,
const double min_distance,
const double tolerance,
const long max_iterations,
const double conservative_rescaling)
const double tmax) const
{
return conservative_piecewise_linear_ccd(
[&](const double t) {
Expand All @@ -223,20 +227,17 @@ bool point_edge_nonlinear_ccd(
output_tolerance, // delta_actual
no_zero_toi); // no zero toi
},
toi, tmax, min_distance, conservative_rescaling);
toi, min_distance, tmax, conservative_rescaling);
}

bool edge_edge_nonlinear_ccd(
bool NonlinearCCD::edge_edge_ccd(
const NonlinearTrajectory& ea0,
const NonlinearTrajectory& ea1,
const NonlinearTrajectory& eb0,
const NonlinearTrajectory& eb1,
double& toi,
const double tmax,
const double min_distance,
const double tolerance,
const long max_iterations,
const double conservative_rescaling)
const double tmax) const
{
return conservative_piecewise_linear_ccd(
[&](const double t) {
Expand Down Expand Up @@ -265,20 +266,17 @@ bool edge_edge_nonlinear_ccd(
output_tolerance, // delta_actual
no_zero_toi); // no zero toi
},
toi, tmax, min_distance, conservative_rescaling);
toi, min_distance, tmax, conservative_rescaling);
}

bool point_triangle_nonlinear_ccd(
bool NonlinearCCD::point_triangle_ccd(
const NonlinearTrajectory& p,
const NonlinearTrajectory& t0,
const NonlinearTrajectory& t1,
const NonlinearTrajectory& t2,
double& toi,
const double tmax,
const double min_distance,
const double tolerance,
const long max_iterations,
const double conservative_rescaling)
const double tmax) const
{
return conservative_piecewise_linear_ccd(
[&](const double t) {
Expand Down Expand Up @@ -306,7 +304,7 @@ bool point_triangle_nonlinear_ccd(
output_tolerance, // delta_actual
no_zero_toi); // no zero toi
},
toi, tmax, min_distance, conservative_rescaling);
toi, min_distance, tmax, conservative_rescaling);
}

} // namespace ipc
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