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Wire is not defined

Hello everyone, this is my first time using manim, manim-physics and GitHub, i hope that i'm doing every fine and respecting all the rules,

So my issue is that i want to create an animation of a magnetic field streamline being blocked by a metallic shield, and as a starter i wanted to try the code provided in the doc, but when i try to input the Wire example in my visual studio i get this message error :

"Wire" is not defined Pylance (reportUndefinedVariable) [Ln 7, Col 16],

How can i solve this ?

Best regards,

Methods don't work

You can't execute any methods once the animations for each object are started. Example:

class WaveScene(Scene):
    def construct(self):
        wave = StandingWave(2, color=YELLOW)

        self.add(wave)

        wave.start_wave()  # Troublemaker

        self.wait(1)
        self.play(
            ApplyMethod(wave.shift, DOWN)
        )
        self.wait(10)

The wave doesn't move down when using wave.start_wave() before.

Make `SpaceScene.make_rigid_body` not take children of `VGroups`

From discord user Naw Sai: SVGMobjects don't work as rigid bodies.

This is because the function SpaceScene.make_rigid_body takes the whole family of the mobject and applies the rigid property; which explains the explosion, as overlap of rigid bodies are considered high powered collisions.

Suggested Changes

I think a good approach would be to make the function disregard families; if the children are intended to be rigid, then an unpacking operator should be used.

Before:

a = VGroup(Circle(), Square().shift(UP*2))
self.make_rigid_body(a)

After:

a = VGroup(Circle(), Square().shift(UP*2))
self.make_rigid_body(*a)

`Charge.point` not updated when moving it

So whenever a Charge object is instanciated, the attribute point is set:

manim-physics/src/manim_physics/electromagnetism.py

Lines 16 to 40 in 70ab45a

class Charge(VGroup):
def __init__(
self,
magnitude: float = 1,
point: np.ndarray = ORIGIN,
add_glow: bool = True,
**kwargs,
) -> None:
"""An electrostatic charge object. Commonly used for :class:`~ElectricField`.
Parameters
----------
magnitude
The strength of the electrostatic charge.
point
The position of the charge.
add_glow
Whether to add a glowing effect. Adds rings of
varying opacities to simulate glowing effect.
kwargs
Additional parameters to be passed to ``VGroup``.
"""
VGroup.__init__(self, **kwargs)
self.magnitude = magnitude
self.point = point

but this attribute is not updated when using methods such as move_to or shift:

class Sample(Scene):
    def construct(self):
        charge = Charge()
        print(charge.point)
        charge.shift(UP)
        print(charge.point)
>>[0. 0. 0.]
>>[0. 0. 0.]

This implies some incorrect behaviour e.g. when using ElectricField.get_force_on_charge:

class Sample(Scene):
    def construct(self):
        charge_1 = Charge(add_glow=False)
        charge_2 = Charge(add_glow=False).shift(UP)
        field = ElectricField(charge_1)
        f = field.get_force_on_charge(charge_2)
        self.add(charge_1, charge_2, field, f)
Result

Sample_ManimCE_v0 15 2

You can see here that the f vector is still located on the origin, where the charge_2 was previously located.

This happens because the code of the get_force_on_charge method is using the charge.point attribute L147:

manim-physics/src/manim_physics/electromagnetism.py

Lines 129 to 149 in 70ab45a

def get_force_on_charge(self, charge: Charge, **kwargs) -> Vector:
"""Returns a vector corresponding to the force
of the electric field on the charge.
"""
p = charge.get_center()
direction = np.zeros(3)
for other_charge in self.charges:
if other_charge == charge:
continue
p0, mag = other_charge.get_center(), other_charge.magnitude
x, y, z = p - p0
dist = np.linalg.norm(p - p0) ** 3
if (x**2) > 0.01 or (y**2) > 0.01:
direction += mag * np.array([x / dist, y / dist, 0])
else:
direction += np.zeros(3)
length = (direction[0] ** 2 + direction[1] ** 2) ** 0.5
vec_start = (
Vector(direction / length * charge.radius).shift(charge.point).get_end()
)
return Vector(direction, **kwargs).shift(vec_start)

So maybe to fix this the methods moving the object such as shift, move_to, to_corner should be overrided? The thing is we can't be 100% sure that all the methods modifying the object's position have been taken into account. Maybe there's a more general way of fixing this.

Turn off gravity for rigid body

I want to turn off gravity for one scene, but methods from pymunk docs does not works.
Firstly I tryied to change scene space gravity paramether in construct method:

def construct(self):
        self.space.gravity = 0, 0```

But it doesn't help
Then i tried to override init method for Space scene class, but it did not bring any result

    def __init__(self, renderer=None, **kwargs):
        self.space = Space(gravity=(0, 0))
        super().__init__(renderer=renderer, **kwargs)

Full code:

from manim import *
from manim_physics import *

class FirstScene(SpaceScene):   
    def __init__(self, renderer=None, **kwargs):
        self.space = Space(gravity=(0, 0))
        super().__init__(renderer=renderer, **kwargs)

    def construct(self):
        self.space.gravity = 0, 0
        c1 = Circle(color="red").shift(2* LEFT)
        c2 = Circle(color="blue").shift(RIGHT)
        self.make_rigid_body(c1, c2)
        c1.body.velocity = (1, 0)
        self.wait(10)

Bump manim version requirement

Manim is currently at version 0.18.0.post0, and remains compatible with manim-physics.

However manim-physics' pyproject specifies:

manim = "^0.17.3"

which causes that any attempt to install manim-physics downgrades installed manim to 0.17.13, and any attempt of upgrading manim after that issues a warning about incompatible requirements with manim-physics.

I think the line in pyproject can be safely changed to:

manim = "^0.17.3,<0.19.0"

make_rigid_body having a bug when applying to string

具体问题发送到群里面了并且私信了
make_rigid_body(string) 只会让最后一个字符掉下去
解决办法：
rigid_mechanics.py 第 56 行和 57 行应该被 indent
要不然只会让字符串的最后一个字符得到效果 而不是每一个字符

Homogeneous magnetic field?

So I'm currently trying to implement a homogeneous magnetic field. However, I can't get it to work. And basically my question is: Is it even possible to create a homogeneous magnetic field using this library?

The closest thing I could get is this (even tough I needed to remove this if-statement in electromagnetism.py, btw, why did you add it?):

from manim import *
from manim_physics import *


class HorseShoeMagnet(VGroup):
    def __init__(
        self,
        width: float = 6,
        height: float = 6,
        bar_width: Optional[float] = None,
        bar_height: Optional[float] = None,
        field_x_padding: Optional[float] = None,
        field_y_padding: Optional[float] = None,
        field_density: float = 2,
        magnets: list[BarMagnet] = None,
        create_bar: bool = True,
        **kwargs
    ):
        magnets = magnets or []
        field_x_padding = field_x_padding or .3
        field_y_padding = field_y_padding or .3
        bar_width = bar_width or 1
        bar_height = bar_height or 1

        field_width = width - bar_width
        field_height = height - (bar_height * 2)

        bar_magnets = [*magnets]
        surrounding_rectangle = Rectangle(width=0, height=height)

        # Ensures that there is a field
        self.bar_magnet = BarMagnet(width=width, height=height * 5)

        if create_bar:
            bar_magnets.insert(0, self.bar_magnet)

        self.field = BarMagneticField(
            *bar_magnets,
            x_range=[
                -(field_width / 2),
                (field_width / 2 - field_x_padding),
                1 / field_density
            ],
            y_range=[
                -(field_height / 2 - field_y_padding),
                (field_height / 2 - field_y_padding),
                1 / field_density
            ]
        )

        self.north_rectangle = Rectangle(
            width=field_width,
            height=bar_height,
            fill_opacity=1,
            color=RED,
            stroke_width=0,
        )\
            .align_to(surrounding_rectangle, DOWN)
        self.north_side_wall = Rectangle(
            width=bar_width,
            height=height / 2,
            fill_opacity=1,
            color=RED,
            stroke_width=0,
        )\
            .align_to(self.north_rectangle, RIGHT + DOWN)\
            .shift(RIGHT)
        self.north_label = Tex("N").next_to(self.north_rectangle, ORIGIN)
        self.north_parts = VGroup(
            self.north_rectangle,
            self.north_side_wall,
        )

        self.south_rectangle = Rectangle(
            width=field_width,
            height=bar_height,
            fill_opacity=1,
            color=BLUE,
            stroke_width=0,
        )\
            .align_to(surrounding_rectangle, UP)
        self.south_side_wall = Rectangle(
            width=bar_width,
            height=height / 2,
            fill_opacity=1,
            color=BLUE,
            stroke_width=0,
        )\
            .align_to(self.south_rectangle, RIGHT + UP)\
            .shift(RIGHT)
        self.south_label = Tex("S").next_to(self.south_rectangle, ORIGIN)
        self.south_parts = VGroup(
            self.south_rectangle,
            self.south_side_wall,
        )

        super().__init__(**kwargs)
        self.add(
            self.field,
            VGroup(
                self.north_parts,
                self.south_parts,
            ),
            self.north_label,
            self.south_label
        )
        self.add(*magnets, self.bar_magnet.set_opacity(.2))


class FirstFormulaExplainedScene(Scene):
    def construct(self):
        magnet = HorseShoeMagnet(field_density=8, magnets=[BarMagnet().scale(.1)])

        self.add(magnet)

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