Value trackers¶

The film's code

import manimgx as m


def curve(x: float) -> float:
    return x**2 / 4


class ValueTrackersHero(m.Scene):
    def construct(self) -> None:
        axes = m.Axes(x_range=[0, 5, 1], y_range=[0, 7, 1], x_length=8, y_length=5)
        graph = axes.plot(curve, color=m.BLUE)
        x = m.ValueTracker(1)
        dot = m.always_redraw(
            lambda: m.Dot(axes.c2p(x.get_value(), curve(x.get_value())), color=m.YELLOW)
        )
        number = m.always_redraw(
            lambda: m.DecimalNumber(x.get_value()).next_to(dot, m.UL)
        )
        self.add(axes, graph, dot, number)
        self.play(x.animate.set_value(4.5), run_time=3)
        self.wait()

A value tracker holds a number and shows nothing. Animate its number with tracker.animate.set_value(10); read it with tracker.get_value() in an updater, or in a function that always_redraw calls. One animation of a tracker then moves every mobject that reads it.

ValueTracker ¶

Code

import manimgx as m


class ValueTrackerExample(m.Scene):
    def construct(self) -> None:
        x = m.ValueTracker(-4)
        line = m.NumberLine(x_range=(-6, 6, 1), length=12).add_numbers()
        pointer = m.Vector(1.5 * m.DOWN, color=m.YELLOW)
        pointer.add_updater(lambda p: p.next_to(line.n2p(x.get_value()), m.UP))
        label = m.MathTex("x", font_size=72, color=m.YELLOW)
        label.add_updater(lambda t: t.next_to(pointer, m.UP))
        self.add(line, pointer, label)
        self.play(x.animate.set_value(5), run_time=2)
        x -= 3
        self.wait(0.5)
        self.play(x.animate.increment_value(-5))

A number that animations can change and updaters can read.

The number is kept as the x coordinate of the tracker's one point, so whatever moves a mobject changes it: tracker.animate.set_value(5) takes it to 5 at the pace of the animation's rate function, and the updaters of other mobjects read it with get_value. A tracker is never drawn; add it to the scene only if it has updaters of its own. tracker += 1 and tracker -= 1 change the number at once.

m.ValueTracker(value=0, **kwargs)

value: The number it starts with.
color: The color of both fill and stroke (default white); None for the class's default.
fill_color: The fill's color; color if not given. Several colors make a gradient along sheen_direction.
fill_opacity: The fill's opacity, from 0 to 1 (default 0: no fill).
stroke_color: The stroke's color; color if not given. Several colors make a gradient.
stroke_opacity: The stroke's opacity, from 0 to 1 (default 1).
stroke_width: The stroke's width, in hundredths of a scene unit (default 4; 0: no stroke).
background_stroke_color: The color of an outline drawn behind the fill (default black).
background_stroke_opacity: The outline's opacity, from 0 to 1 (default 1).
background_stroke_width: The outline's width, in hundredths of a scene unit (default 0: none).
sheen_factor: How much the colors lighten toward sheen_direction, from -1 to 1 (default 0); a negative factor darkens.
sheen_direction: The direction the colors lighten toward (default UL).
joint_type: How the stroke is joined where its path turns: round, beveled or mitered, as a two-dimensional scene draws it (see LineJointType; default AUTO: mitered).
cap_style: How the stroke ends, at each end it shows (an open path's, a dash's): round, butt or square, as a two-dimensional scene draws it (see CapStyleType; default AUTO: butt).
shade_in_3d: Whether a three-dimensional scene's light shades the mobject.
material: How its surface reflects the scene's lights in a three-dimensional scene (see Material); None: Manim's shading (default).
name: A name for the mobject; its class's name if not given.
z_index: Its place in the drawing order: a higher index is drawn over a lower one (default 0).
target: The state MoveToTarget moves the mobject to.

It also takes the style keywords.

Source

src/manimgx/mobject.py

def __init__(self, value: V = 0, **kwargs: Unpack[Style]) -> None:
    super().__init__(**kwargs)
    self.points = np.zeros((1, 3))
    self.set_value(value)

get_value ¶

The number the tracker holds.

tracker.get_value()

Source

src/manimgx/mobject.py

def get_value(self) -> V:
    """The number the tracker holds."""
    return float(self.points[0, 0])  # pyright: ignore[reportReturnType]  # V is float here

set_value ¶

Set the number the tracker holds; through animate, animate it there.

tracker.set_value(value)

value: The new number.

Source

src/manimgx/mobject.py

def set_value(self, value: V) -> Self:
    """Set the number the tracker holds; through
    [`animate`][manimgx.Mobject.animate], animate it there.

    Args:
        value: The new number.
    """
    points = np.array(self.points)
    points[0, 0] = value
    self.points = points
    return self

increment_value ¶

Add to the number the tracker holds; through animate, animate the change.

tracker.increment_value(d_value)

d_value: The amount to add; a negative one subtracts.

Source

src/manimgx/mobject.py

def increment_value(self, d_value: V) -> Self:
    """Add to the number the tracker holds; through
    [`animate`][manimgx.Mobject.animate], animate the change.

    Args:
        d_value: The amount to add; a negative one subtracts.
    """
    return self.set_value(self.get_value() + d_value)

ComplexValueTracker ¶

Code

import manimgx as m


class ComplexValueTrackerExample(m.Scene):
    def construct(self) -> None:
        plane = m.ComplexPlane().add_coordinates()
        z = m.ComplexValueTracker(2 + 1j)
        dot = m.Dot(radius=0.15, color=m.YELLOW)
        dot.add_updater(lambda d: d.move_to(plane.n2p(z.get_value())))
        self.add(plane, dot)
        self.play(z.animate.set_value(-3 + 2j))
        self.play(z.animate.set_value(z.get_value() * 1j))
        self.play(z.animate.set_value(z.get_value() / (1 + 1j)))

A complex number that animations can change and updaters can read.

The number is kept as the tracker's one point, its real part as x and its imaginary part as y, so an animation takes it along a straight line of the complex plane: tracker.animate.set_value(3 + 2j). += and -= change it at once, in complex arithmetic.

m.ComplexValueTracker(value=0, **kwargs)

value: The number it starts with.
color: The color of both fill and stroke (default white); None for the class's default.
fill_color: The fill's color; color if not given. Several colors make a gradient along sheen_direction.
fill_opacity: The fill's opacity, from 0 to 1 (default 0: no fill).
stroke_color: The stroke's color; color if not given. Several colors make a gradient.
stroke_opacity: The stroke's opacity, from 0 to 1 (default 1).
stroke_width: The stroke's width, in hundredths of a scene unit (default 4; 0: no stroke).
background_stroke_color: The color of an outline drawn behind the fill (default black).
background_stroke_opacity: The outline's opacity, from 0 to 1 (default 1).
background_stroke_width: The outline's width, in hundredths of a scene unit (default 0: none).
sheen_factor: How much the colors lighten toward sheen_direction, from -1 to 1 (default 0); a negative factor darkens.
sheen_direction: The direction the colors lighten toward (default UL).
joint_type: How the stroke is joined where its path turns: round, beveled or mitered, as a two-dimensional scene draws it (see LineJointType; default AUTO: mitered).
cap_style: How the stroke ends, at each end it shows (an open path's, a dash's): round, butt or square, as a two-dimensional scene draws it (see CapStyleType; default AUTO: butt).
shade_in_3d: Whether a three-dimensional scene's light shades the mobject.
material: How its surface reflects the scene's lights in a three-dimensional scene (see Material); None: Manim's shading (default).
name: A name for the mobject; its class's name if not given.
z_index: Its place in the drawing order: a higher index is drawn over a lower one (default 0).
target: The state MoveToTarget moves the mobject to.

It also takes the style keywords.

Source

src/manimgx/mobject.py

def __init__(self, value: V = 0, **kwargs: Unpack[Style]) -> None:
    super().__init__(**kwargs)
    self.points = np.zeros((1, 3))
    self.set_value(value)

get_value ¶

The complex number the tracker holds.

tracker.get_value()

Source

src/manimgx/mobject.py

def get_value(self) -> complex:
    """The complex number the tracker holds."""
    return complex(*self.points[0, :2])

set_value ¶

Set the complex number the tracker holds; through animate, animate it there, in a straight line.

tracker.set_value(value)

value: The new number; a real one is taken as complex.

Source

src/manimgx/mobject.py

def set_value(self, value: complex) -> Self:
    """Set the complex number the tracker holds; through
    [`animate`][manimgx.Mobject.animate], animate it there, in a straight line.

    Args:
        value: The new number; a real one is taken as complex.
    """
    z = complex(value)
    points = np.array(self.points)
    points[0, :2] = (z.real, z.imag)
    self.points = points
    return self