样例学习

examples.py 提供了一些样例

HelloJAnimExample

from janim.imports import *

class HelloJAnimExample(Timeline):
    def construct(self):
        # define items
        circle = Circle(color=BLUE)
        square = Square(color=GREEN, fill_alpha=0.5)

        # do animations
        self.forward()
        self.play(Create(circle))
        self.play(Transform(circle, square))
        self.play(Uncreate(square))
        self.forward()

SimpleCurveExample

from janim.imports import *

class SimpleCurveExample(Timeline):
    def construct(self):
        item1 = VItem(
            LEFT * 2, DR, UR * 3 + UP, RIGHT * 4, DR * 2, DOWN * 2, LEFT * 2,
            NAN_POINT,
            DL * 3, DL * 2, DOWN * 3, DL * 4, DL * 3,
        )
        item1.fill.set(alpha=0.5)
        item1.show()

        self.forward(0.5)
        self.play(item1.anim.color.set(BLUE))
        self.play(Rotate(item1, -90 * DEGREES))
        self.forward(0.5)

        item2 = VItem(LEFT, UP, RIGHT, DOWN, LEFT)
        item2.color.set(BLUE)
        item2.fill.set(alpha=0.2)

        state = self.camera.copy()
        self.play(self.camera.anim.points.scale(0.5))
        self.play(self.camera.anim.become(state))

        self.play(
            Transform(item1, item2),
            duration=2
        )
        self.forward(1)

TextExample

from janim.imports import *

class TextExample(Timeline):
    def construct(self):
        txt = Text('Here is a text', font_size=64)
        desc = Group(
            Text('You can also apply <c BLUE>styles</c> to the text.', format=Text.Format.RichText),
            Text('You can also apply <c GREEN><fs 1.4>styles</fs></c> to the text.', format=Text.Format.RichText),
        )
        group = Group(txt, desc)
        group.points.arrange(DOWN, buff=MED_LARGE_BUFF)

        self.forward()
        self.play(Write(txt))
        self.play(FadeIn(desc[0], UP))
        self.play(Transform(desc[0], desc[1]))
        self.forward()

TypstExample

from janim.imports import *

typst_doc = '''
JAnim provides #text(green)[`TypstDoc`] class to insert typst document.

Math expressions are also available.

$ A = pi r^2 $
$ "area" = pi dot "radius"^2 $
$ cal(A) :=
    { x in RR | x "is natural" } $
#let x = 5
$ #x < 17 $

The difference between #text(green)[`TypstDoc`] and #text(green)[`Typst`]:
- #text(green)[`TypstDoc`] automatically align to the top of view,
so you can see the document from the start.
- The content of #text(green)[`Typst`] is wrapped by math environment
and move to the center by default.
'''


class TypstExample(Timeline):
    def construct(self):
        doc = TypstDoc(typst_doc)
        typ = Typst('sum_(i=1)^n x_i')

        # Applying animations on text is slow
        self.play(Write(doc), duration=4)
        self.forward()
        self.play(FadeOut(doc))

        self.play(Write(typ))
        self.forward()
        self.play(FadeOut(typ))

AnimatingPiExample

from janim.imports import *

class AnimatingPiExample(Timeline):
    def construct(self):
        grid = Typst('pi') * 100
        grid.points.scale(2).arrange_in_grid(10, 10, buff=0.2)
        grid.show()

        self.play(grid.anim.points.shift(LEFT))
        self.play(grid(VItem).anim.color.set(YELLOW))
        self.forward()
        self.play(grid(VItem).anim.color.set(BLUE))
        self.forward()
        self.play(grid.anim.points.to_center().set_height(TAU - MED_SMALL_BUFF))
        self.forward()

        self.play(grid.anim.points.apply_complex_fn(np.exp), duration=5)
        self.forward()

        self.play(
            grid.anim.points.apply_point_fn(
                lambda p: [
                    p[0] + 0.5 * math.sin(p[1]),
                    p[1] + 0.5 * math.sin(p[0]),
                    p[2]
                ]
            ),
            duration=5
        )
        self.forward()

NumberPlaneExample

from janim.imports import *

class NumberPlaneExample(Timeline):
    def construct(self):
        plane = NumberPlane(faded_line_ratio=1)

        sin_graph = plane.get_graph(lambda x: math.sin(x))

        self.forward(0.2)
        self.play(Write(plane, lag_ratio=0.05))
        self.play(Write(sin_graph))
        self.forward()

        self.play(
            sin_graph.anim(),
            plane.anim.points.apply_matrix([
                [3, -1],
                [1, 2]
            ]),
            duration=2
        )
        self.forward()

UpdaterExample

from janim.imports import *

class UpdaterExample(Timeline):
    def construct(self):
        square = Square(fill_color=BLUE_E, fill_alpha=1).show()
        brace = Brace(square, UP).show()

        def text_updater(p: UpdaterParams):
            cmpt = brace.current().points
            return cmpt.create_text(f'Width = {cmpt.brace_length:.2f}')

        self.prepare(
            DataUpdater(
                brace,
                lambda data, p: data.points.match(square.current())
            ),
            ItemUpdater(None, text_updater),
            duration=10
        )
        self.forward()
        self.play(square.anim.points.scale(2))
        self.play(square.anim.points.scale(0.5))
        self.play(square.anim.points.set_width(5, stretch=True))

        w0 = square.points.box.width

        self.play(
            DataUpdater(
                square,
                lambda data, p: data.points.set_width(
                    w0 + 0.5 * w0 * math.sin(p.alpha * p.range.duration)
                )
            ),
            duration=5
        )
        self.forward()