lizzy/rigid-body
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added friction

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2026-03-11 16:07:40 -04:00
parent 5742b4613e
commit 010d50d5bb
4 changed files with 82 additions and 12 deletions
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34
rigidbody.py
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@@ -14,6 +14,12 @@ class RigidBody:
angular_velocity: float = 0
mass: float = 1.0
restitution: float = 0.5
coef_friction: float = 0.6
def apply_impulse(self, j: pg.Vector2, point: pg.Vector2) -> None:
moment_arm = point - self.transform.global_position
self.velocity += j * self.inv_mass
self.angular_velocity += moment_arm.cross(j) * self.inv_moment_of_inertia
@property
def inv_mass(self) -> float:
@@ -57,20 +63,30 @@ class PhysicsSystem:
if b.mass != 0.0:
b.transform.position -= correction
restitution = a.restitution * b.restitution
friction = a.coef_friction * b.coef_friction
tangent = collision.normal.rotate(90)
v_rel_linear = pg.Vector2(a.velocity - b.velocity)
a_w = a.angular_velocity
b_w = b.angular_velocity
for point in collision.points:
r_a = point - a.transform.position
r_b = point - b.transform.position
w_cross_r_a = pg.Vector2(-r_a.y * a.angular_velocity, r_a.x * a.angular_velocity) #omega is not encoded as a vector, so we pretend it is
w_cross_r_b = pg.Vector2(-r_b.y * b.angular_velocity, r_b.x * b.angular_velocity)
v_rel = a.velocity + w_cross_r_a - b.velocity - w_cross_r_b
restitution = a.restitution * b.restitution
impulse = -(1+restitution)*(v_rel.dot(collision.normal))\
w_cross_r_a = pg.Vector2(-r_a.y * a_w, r_a.x * a_w) #omega is not encoded as a vector, so we pretend it is
w_cross_r_b = pg.Vector2(-r_b.y * b_w, r_b.x * b_w)
v_rel = v_rel_linear + w_cross_r_a - w_cross_r_b
v_rel_tangent = v_rel.dot(tangent)
collision_impulse = -(1+restitution)*(v_rel.dot(collision.normal))\
/ (a.inv_mass + b.inv_mass + (r_a.cross(collision.normal)**2 * a.inv_moment_of_inertia)\
+ (r_b.cross(collision.normal)**2 * b.inv_moment_of_inertia)) / len(collision.points)
a.velocity += collision.normal*impulse*a.inv_mass
b.velocity -= collision.normal*impulse*b.inv_mass
a.angular_velocity += (r_a.cross(impulse*collision.normal)) * a.inv_moment_of_inertia
b.angular_velocity -= (r_b.cross(impulse*collision.normal)) * b.inv_moment_of_inertia
friction_impulse = (-v_rel_tangent / (a.inv_mass + b.inv_mass +\
(r_a.cross(tangent))**2 * a.inv_moment_of_inertia +\
(r_b.cross(tangent)**2 * b.inv_moment_of_inertia))) / len(collision.points)
friction_impulse = pg.math.clamp(friction_impulse, -abs(collision_impulse)*friction, abs(collision_impulse)*friction)
a.apply_impulse(collision.normal*collision_impulse + friction_impulse * tangent, point)
b.apply_impulse(-1 * collision.normal*collision_impulse - friction_impulse * tangent, point)