"""
Copyright 2023 Ethan Christensen
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
"""
import numpy as np
from bruhcolor import bruhcolored as bc
from ..bruhutil import Buffer
from ._resize import raster
from .base_effect import BaseEffect
from .settings import BoidsSettings, validated_settings
def _heat(r: float) -> int:
r = max(0.0, min(1.0, r))
if r < 0.25:
return 17 + int(r * 4 * 18)
elif r < 0.5:
return 51 + int((r - 0.25) * 4 * 12)
elif r < 0.75:
return 82 + int((r - 0.5) * 4 * 12)
else:
return 220 + int((r - 0.75) * 4 * 3)
[docs]
class BoidsEffect(BaseEffect):
"""
Reynolds flocking simulation.
Each boid obeys three rules:
- **Separation** — steer away from close neighbours
- **Alignment** — match average velocity of nearby flock
- **Cohesion** — move toward average position of nearby flock
Boids wrap around screen edges. Speed is colour-mapped hot (fast) to
cool (slow) when *color* is enabled.
"""
[docs]
def __init__(
self, buffer: Buffer, background: str, settings: BoidsSettings | None = None
):
s = validated_settings(settings, BoidsSettings)
super().__init__(buffer, background, seed=s.seed)
self.color = s.color
self.char = s.char
self.max_speed = s.max_speed
self.perception = s.perception
self._w = buffer.width()
self._h = buffer.height()
rng = self.np_rng
n = s.num_boids
self._pos = np.column_stack(
[
rng.uniform(0, self._w, n),
rng.uniform(0, self._h, n),
]
)
self._vel = np.column_stack(
[
rng.uniform(-0.8, 0.8, n),
rng.uniform(-0.4, 0.4, n),
]
)
[docs]
def update(self, dt: float) -> None:
"""Advance one simulation tick; dt is measured in seconds."""
pos = self._pos
vel = self._vel
diff = pos[:, np.newaxis, :] - pos[np.newaxis, :, :]
dist = np.sqrt((diff**2).sum(axis=2))
np.fill_diagonal(dist, np.inf)
nbr = dist < self.perception
close = dist < self.perception * 0.28
has_nbr = nbr.any(axis=1, keepdims=True)
n_nbr = nbr.sum(axis=1, keepdims=True).clip(1, None)
sep = np.where(close[:, :, np.newaxis], diff, 0.0).sum(axis=1) * 0.12
vel_sum = np.where(nbr[:, :, np.newaxis], vel[np.newaxis], 0.0).sum(axis=1)
align = np.where(has_nbr, (vel_sum / n_nbr - vel) * 0.05, 0.0)
pos_sum = np.where(nbr[:, :, np.newaxis], pos[np.newaxis], 0.0).sum(axis=1)
cohesion = np.where(has_nbr, (pos_sum / n_nbr - pos) * 0.003, 0.0)
new_vel = vel + sep + align + cohesion
new_vel += self.np_rng.uniform(-0.02, 0.02, new_vel.shape)
speeds = np.linalg.norm(new_vel, axis=1, keepdims=True).clip(1e-8)
new_vel = np.where(
speeds > self.max_speed, new_vel / speeds * self.max_speed, new_vel
)
new_vel = np.where(speeds < 0.3, new_vel / speeds * 0.3, new_vel)
new_pos = (pos + new_vel) % np.array([[self._w, self._h]])
self._pos = new_pos
self._vel = new_vel
self._paint()
def _paint(self) -> None:
self.buffer.clear_buffer(val=self.background)
new_pos, new_vel = self._pos, self._vel
xs = new_pos[:, 0].astype(int)
ys = new_pos[:, 1].astype(int)
spd_norm = (np.linalg.norm(new_vel, axis=1) / max(self.max_speed, 1e-8)).clip(
0, 1
)
valid = (xs >= 0) & (xs < self._w) & (ys >= 0) & (ys < self._h)
for i in np.where(valid)[0]:
color = _heat(float(spd_norm[i])) if self.color else None
ch = bc(self.char, color=color) if color is not None else self.char
self.buffer.put_char(int(xs[i]), int(ys[i]), ch)
[docs]
def resize(self, size: tuple[int, int]) -> None:
"""Wrap positions into the new bounds, preserving flock size and velocities."""
self.buffer = raster(self.buffer, size, self.background)
self._w, self._h = size
self._pos %= np.array([[self._w, self._h]])
self._paint()
super().resize(size)