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133 lines
5.3 KiB
ReStructuredText
133 lines
5.3 KiB
ReStructuredText
Learning by Example
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===================
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You create videos in manim by writing :class:`~scene.scene.Scene` instances.
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``example_scenes.py`` contains a few simple ones that we can use to learn about
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manim. For instance, take ``SquareToCircle``.
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.. code-block:: python
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:linenos:
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class SquareToCircle(Scene):
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def construct(self):
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circle = Circle()
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square = Square()
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square.flip(RIGHT)
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square.rotate(-3 * TAU / 8)
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circle.set_fill(PINK, opacity=0.5)
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self.play(ShowCreation(square))
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self.play(Transform(square, circle))
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self.play(FadeOut(square))
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:meth:`~scene.scene.Scene.construct` specifies what is displayed on the screen
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when the :class:`~scene.scene.Scene` is rendered to video. You can render a
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:class:`~scene.scene.Scene` by running ``extract_scene.py``. Run ``python
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extract_scene.py -h`` to see how it's used.
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.. code-block:: none
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> python extract_scene.py -h
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usage: extract_scene.py [-h] [-p] [-w] [-s] [-l] [-m] [-g] [-f] [-t] [-q] [-a]
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[-o OUTPUT_NAME] [-n START_AT_ANIMATION_NUMBER]
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[-r RESOLUTION] [-c COLOR] [-d OUTPUT_DIRECTORY]
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file [scene_name]
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positional arguments:
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file path to file holding the python code for the scene
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scene_name Name of the Scene class you want to see
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optional arguments:
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-h, --help show this help message and exit
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-p, --preview
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-w, --write_to_movie
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-s, --show_last_frame
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-l, --low_quality
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-m, --medium_quality
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-g, --save_pngs
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-f, --show_file_in_finder
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-t, --transparent
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-q, --quiet
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-a, --write_all
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-o OUTPUT_NAME, --output_name OUTPUT_NAME
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-n START_AT_ANIMATION_NUMBER, --start_at_animation_number START_AT_ANIMATION_NUMBER
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-r RESOLUTION, --resolution RESOLUTION
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-c COLOR, --color COLOR
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-d OUTPUT_DIRECTORY, --output_directory OUTPUT_DIRECTORY
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The most common flags are ``-p``, to automatically play the generated video,
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``-l``, to render in lower quality in favor of speed, and ``-s``, to show the
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last frame of the :class:`~scene.scene.Scene` for faster development. Run
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``python extract_scene.py example_scenes.py SquareToCircle -pl`` to produce a
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file called SquareToCircle.mp4 in the media directory that you have configured,
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and automatically play it.
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.. raw:: html
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<iframe width="560" height="315" src="https://www.youtube.com/embed/8tvYDIGLJJA?ecver=1" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>
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Let's step through each line of the :class:`~scene.scene.Scene`. Lines 3 and 4
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instantiate a :class:`~mobject.geometry.Circle` and
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:class:`~mobject.geometry.Square`, respectively. Both of these subclass
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:class:`~mobject.mobject.Mobject`, the base class for objects in manim. Note
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that instantiating a :class:`~mobject.mobject.Mobject` does not add it to the
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:class:`~scene.scene.Scene`, so you wouldn't see anything if you were to render
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the :class:`~scene.scene.Scene` at this point.
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.. code-block:: python
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:linenos:
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:lineno-start: 3
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circle = Circle()
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square = Square()
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Lines 5, 6, and 7 apply various modifications to the mobjects before animating
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them. The call to :meth:`~mobject.mobject.Mobject.flip` on line 5 flips the
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:class:`~mobject.geometry.Square` across the RIGHT vector. This is equivalent
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to a refection across the x-axis. Then the call to
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:meth:`~mobject.mobject.Mobject.rotate` on line 6 rotates the
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:class:`~mobject.geometry.Square` 3/8ths of a full rotation counterclockwise.
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Finally, the call to :meth:`~mobject.mobject.Mobject.set_fill` on line 7 sets
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the fill color for the :class:`~mobject.geometry.Circle` to pink, and its
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opacity to 0.5.
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.. code-block:: python
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:linenos:
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:lineno-start: 5
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square.flip(RIGHT)
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square.rotate(-3 * TAU / 8)
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circle.set_fill(PINK, opacity=0.5)
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Line 9 is the first to generate video.
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:class:`~animation.creation.ShowCreation`,
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:class:`~animation.transform.Transform`, and
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:class:`~animation.creation.FadeOut` are
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:class:`~animation.animation.Animation` instances. Each
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:class:`~animation.animation.Animation` takes one or more
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:class:`~mobject.mobject.Mobject` instances as arguments, which it animates
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when passed to :meth:`~scene.scene.Scene.play`. This is how video is typically
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created in manim. :class:`~mobject.mobject.Mobject` instances are automatically
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added to the :class:`~scene.scene.Scene` when they are animated. You can add a
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:class:`~mobject.mobject.Mobject` to the :class:`~scene.scene.Scene` manually
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by passing it as an argument to :meth:`~scene.scene.Scene.add`.
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.. code-block:: python
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:linenos:
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:lineno-start: 9
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self.play(ShowCreation(square))
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self.play(Transform(square, circle))
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self.play(FadeOut(square))
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:class:`~animation.creation.ShowCreation` draws a
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:class:`~mobject.mobject.Mobject` to the screen,
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:class:`~animation.transform.Transform` morphs one
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:class:`~mobject.mobject.Mobject` into another, and
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:class:`~animation.creation.FadeOut` fades a
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:class:`~mobject.mobject.Mobject` out of the :class:`~scene.scene.Scene`. Note
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that only the first argument to :class:`~animation.transform.Transform` is
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modified, and the second is not added to the :class:`~scene.scene.Scene`. After
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line 10 is executed ``square`` is a :class:`~mobject.geometry.Square` instance
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with the shape of a :class:`~mobject.geometry.Circle`.
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