Allow animations with run_time=0 and implement convenience Add animation (#4017)

* Allow animations with run_time=0 and implement convenience Add animation

* Modify examples so that there are less characters per line

* Docstring fixes

* Update manim/animation/animation.py

* Address comments

---------

Co-authored-by: Benjamin Hackl <[email protected]>

Author: chopan050

manim/animation/animation.py

@@ -7,17 +7,17 @@
 from .. import config, logger
 from ..constants import RendererType
 from ..mobject import mobject
-from ..mobject.mobject import Mobject
+from ..mobject.mobject import Group, Mobject
 from ..mobject.opengl import opengl_mobject
 from ..utils.rate_functions import linear, smooth
 
-__all__ = ["Animation", "Wait", "override_animation"]
+__all__ = ["Animation", "Wait", "Add", "override_animation"]
 
 
 from collections.abc import Iterable, Sequence
 from copy import deepcopy
 from functools import partialmethod
-from typing import TYPE_CHECKING, Callable
+from typing import TYPE_CHECKING, Any, Callable
 
 from typing_extensions import Self
 
@@ -172,6 +172,19 @@ def __init__(
                 ),
             )
 
+    @property
+    def run_time(self) -> float:
+        return self._run_time
+
+    @run_time.setter
+    def run_time(self, value: float) -> None:
+        if value < 0:
+            raise ValueError(
+                f"The run_time of {self.__class__.__name__} cannot be "
+                f"negative. The given value was {value}."
+            )
+        self._run_time = value
+
     def _typecheck_input(self, mobject: Mobject | None) -> None:
         if mobject is None:
             logger.debug("Animation with empty mobject")
@@ -194,7 +207,6 @@ def begin(self) -> None:
         method.
 
         """
-        self.run_time = validate_run_time(self.run_time, str(self))
         self.starting_mobject = self.create_starting_mobject()
         if self.suspend_mobject_updating:
             # All calls to self.mobject's internal updaters
@@ -569,33 +581,6 @@ def prepare_animation(
     raise TypeError(f"Object {anim} cannot be converted to an animation")
 
 
-def validate_run_time(
-    run_time: float, caller_name: str, parameter_name: str = "run_time"
-) -> float:
-    if run_time <= 0:
-        raise ValueError(
-            f"{caller_name} has a {parameter_name} of {run_time:g} <= 0 "
-            f"seconds which Manim cannot render. Please set the "
-            f"{parameter_name} to a positive number."
-        )
-
-    # config.frame_rate holds the number of frames per second
-    fps = config.frame_rate
-    seconds_per_frame = 1 / fps
-    if run_time < seconds_per_frame:
-        logger.warning(
-            f"The original {parameter_name} of {caller_name}, {run_time:g} "
-            f"seconds, is too short for the current frame rate of {fps:g} "
-            f"FPS. Rendering with the shortest possible {parameter_name} of "
-            f"{seconds_per_frame:g} seconds instead."
-        )
-        new_run_time = seconds_per_frame
-    else:
-        new_run_time = run_time
-
-    return new_run_time
-
-
 class Wait(Animation):
     """A "no operation" animation.
 
@@ -638,7 +623,91 @@ def __init__(
         self.mobject.shader_wrapper_list = []
 
     def begin(self) -> None:
-        self.run_time = validate_run_time(self.run_time, str(self))
+        pass
+
+    def finish(self) -> None:
+        pass
+
+    def clean_up_from_scene(self, scene: Scene) -> None:
+        pass
+
+    def update_mobjects(self, dt: float) -> None:
+        pass
+
+    def interpolate(self, alpha: float) -> None:
+        pass
+
+
+class Add(Animation):
+    """Add Mobjects to a scene, without animating them in any other way. This
+    is similar to the :meth:`.Scene.add` method, but :class:`Add` is an
+    animation which can be grouped into other animations.
+
+    Parameters
+    ----------
+    mobjects
+        One :class:`~.Mobject` or more to add to a scene.
+    run_time
+        The duration of the animation after adding the ``mobjects``. Defaults
+        to 0, which means this is an instant animation without extra wait time
+        after adding them.
+    **kwargs
+        Additional arguments to pass to the parent :class:`Animation` class.
+
+    Examples
+    --------
+
+    .. manim:: DefaultAddScene
+
+        class DefaultAddScene(Scene):
+            def construct(self):
+                text_1 = Text("I was added with Add!")
+                text_2 = Text("Me too!")
+                text_3 = Text("And me!")
+                texts = VGroup(text_1, text_2, text_3).arrange(DOWN)
+                rect = SurroundingRectangle(texts, buff=0.5)
+
+                self.play(
+                    Create(rect, run_time=3.0),
+                    Succession(
+                        Wait(1.0),
+                        # You can Add a Mobject in the middle of an animation...
+                        Add(text_1),
+                        Wait(1.0),
+                        # ...or multiple Mobjects at once!
+                        Add(text_2, text_3),
+                    ),
+                )
+                self.wait()
+
+    .. manim:: AddWithRunTimeScene
+
+        class AddWithRunTimeScene(Scene):
+            def construct(self):
+                # A 5x5 grid of circles
+                circles = VGroup(
+                    *[Circle(radius=0.5) for _ in range(25)]
+                ).arrange_in_grid(5, 5)
+
+                self.play(
+                    Succession(
+                        # Add a run_time of 0.2 to wait for 0.2 seconds after
+                        # adding the circle, instead of using Wait(0.2) after Add!
+                        *[Add(circle, run_time=0.2) for circle in circles],
+                        rate_func=smooth,
+                    )
+                )
+                self.wait()
+    """
+
+    def __init__(
+        self, *mobjects: Mobject, run_time: float = 0.0, **kwargs: Any
+    ) -> None:
+        mobject = mobjects[0] if len(mobjects) == 1 else Group(*mobjects)
+        super().__init__(mobject, run_time=run_time, introducer=True, **kwargs)
+
+    def begin(self) -> None:
+        pass
 
     def finish(self) -> None:
         pass

manim/animation/composition.py

@@ -9,7 +9,7 @@
 import numpy as np
 
 from manim._config import config
-from manim.animation.animation import Animation, prepare_animation, validate_run_time
+from manim.animation.animation import Animation, prepare_animation
 from manim.constants import RendererType
 from manim.mobject.mobject import Group, Mobject
 from manim.mobject.opengl.opengl_mobject import OpenGLGroup
@@ -87,7 +87,6 @@ def begin(self) -> None:
                 f"Trying to play {self} without animations, this is not supported. "
                 "Please add at least one subanimation."
             )
-        self.run_time = validate_run_time(self.run_time, str(self))
         self.anim_group_time = 0.0
         if self.suspend_mobject_updating:
             self.group.suspend_updating()
@@ -175,11 +174,13 @@ def interpolate(self, alpha: float) -> None:
         ]
 
         run_times = to_update["end"] - to_update["start"]
+        with_zero_run_time = run_times == 0
+        run_times[with_zero_run_time] = 1
         sub_alphas = (anim_group_time - to_update["start"]) / run_times
         if time_goes_back:
-            sub_alphas[sub_alphas < 0] = 0
+            sub_alphas[(sub_alphas < 0) | with_zero_run_time] = 0
         else:
-            sub_alphas[sub_alphas > 1] = 1
+            sub_alphas[(sub_alphas > 1) | with_zero_run_time] = 1
 
         for anim_to_update, sub_alpha in zip(to_update["anim"], sub_alphas):
             anim_to_update.interpolate(sub_alpha)
@@ -235,7 +236,6 @@ def begin(self) -> None:
                 f"Trying to play {self} without animations, this is not supported. "
                 "Please add at least one subanimation."
             )
-        self.run_time = validate_run_time(self.run_time, str(self))
         self.update_active_animation(0)
 
     def finish(self) -> None:

manim/scene/scene.py

@@ -37,7 +37,7 @@
 from manim.mobject.opengl.opengl_mobject import OpenGLPoint
 
 from .. import config, logger
-from ..animation.animation import Animation, Wait, prepare_animation, validate_run_time
+from ..animation.animation import Animation, Wait, prepare_animation
 from ..camera.camera import Camera
 from ..constants import *
 from ..gui.gui import configure_pygui
@@ -1020,6 +1020,35 @@ def get_time_progression(
         )
         return time_progression
 
+    @classmethod
+    def validate_run_time(
+        cls,
+        run_time: float,
+        method: Callable[[Any, ...], Any],
+        parameter_name: str = "run_time",
+    ) -> float:
+        method_name = f"{cls.__name__}.{method.__name__}()"
+        if run_time <= 0:
+            raise ValueError(
+                f"{method_name} has a {parameter_name} of "
+                f"{run_time:g} <= 0 seconds which Manim cannot render. "
+                f"The {parameter_name} must be a positive number."
+            )
+
+        # config.frame_rate holds the number of frames per second
+        fps = config.frame_rate
+        seconds_per_frame = 1 / fps
+        if run_time < seconds_per_frame:
+            logger.warning(
+                f"The original {parameter_name} of {method_name}, "
+                f"{run_time:g} seconds, is too short for the current frame "
+                f"rate of {fps:g} FPS. Rendering with the shortest possible "
+                f"{parameter_name} of {seconds_per_frame:g} seconds instead."
+            )
+            run_time = seconds_per_frame
+
+        return run_time
+
     def get_run_time(self, animations: list[Animation]):
         """
         Gets the total run time for a list of animations.
@@ -1035,7 +1064,9 @@ def get_run_time(self, animations: list[Animation]):
         float
             The total ``run_time`` of all of the animations in the list.
         """
-        return max(animation.run_time for animation in animations)
+        run_time = max(animation.run_time for animation in animations)
+        run_time = self.validate_run_time(run_time, self.play, "total run_time")
+        return run_time
 
     def play(
         self,
@@ -1131,7 +1162,7 @@ def wait(
         --------
         :class:`.Wait`, :meth:`.should_mobjects_update`
         """
-        duration = validate_run_time(duration, str(self) + ".wait()", "duration")
+        duration = self.validate_run_time(duration, self.wait, "duration")
         self.play(
             Wait(
                 run_time=duration,
@@ -1155,7 +1186,7 @@ def pause(self, duration: float = DEFAULT_WAIT_TIME):
         --------
         :meth:`.wait`, :class:`.Wait`
         """
-        duration = validate_run_time(duration, str(self) + ".pause()", "duration")
+        duration = self.validate_run_time(duration, self.pause, "duration")
         self.wait(duration=duration, frozen_frame=True)
 
     def wait_until(self, stop_condition: Callable[[], bool], max_time: float = 60):
@@ -1169,7 +1200,7 @@ def wait_until(self, stop_condition: Callable[[], bool], max_time: float = 60):
         max_time
             The maximum wait time in seconds.
         """
-        max_time = validate_run_time(max_time, str(self) + ".wait_until()", "max_time")
+        max_time = self.validate_run_time(max_time, self.wait_until, "max_time")
         self.wait(max_time, stop_condition=stop_condition)
 
     def compile_animation_data(

tests/module/animation/test_animation.py

@@ -5,16 +5,22 @@
 from manim import FadeIn, Scene
 
 
-@pytest.mark.parametrize(
-    "run_time",
-    [0, -1],
-)
-def test_animation_forbidden_run_time(run_time):
+def test_animation_zero_total_run_time():
     test_scene = Scene()
     with pytest.raises(
-        ValueError, match="Please set the run_time to a positive number."
+        ValueError, match="The total run_time must be a positive number."
     ):
-        test_scene.play(FadeIn(None, run_time=run_time))
+        test_scene.play(FadeIn(None, run_time=0))
+
+
+def test_single_animation_zero_run_time_with_more_animations():
+    test_scene = Scene()
+    test_scene.play(FadeIn(None, run_time=0), FadeIn(None, run_time=1))
+
+
+def test_animation_negative_run_time():
+    with pytest.raises(ValueError, match="The run_time of FadeIn cannot be negative."):
+        FadeIn(None, run_time=-1)
 
 
 def test_animation_run_time_shorter_than_frame_rate(manim_caplog, config):
@@ -23,8 +29,29 @@ def test_animation_run_time_shorter_than_frame_rate(manim_caplog, config):
     assert "too short for the current frame rate" in manim_caplog.text
 
 
+@pytest.mark.parametrize("duration", [0, -1])
+def test_wait_invalid_duration(duration):
+    test_scene = Scene()
+    with pytest.raises(ValueError, match="The duration must be a positive number."):
+        test_scene.wait(duration)
+
+
 @pytest.mark.parametrize("frozen_frame", [False, True])
-def test_wait_run_time_shorter_than_frame_rate(manim_caplog, frozen_frame):
+def test_wait_duration_shorter_than_frame_rate(manim_caplog, frozen_frame):
     test_scene = Scene()
     test_scene.wait(1e-9, frozen_frame=frozen_frame)
     assert "too short for the current frame rate" in manim_caplog.text
+
+
+@pytest.mark.parametrize("duration", [0, -1])
+def test_pause_invalid_duration(duration):
+    test_scene = Scene()
+    with pytest.raises(ValueError, match="The duration must be a positive number."):
+        test_scene.pause(duration)
+
+
+@pytest.mark.parametrize("max_time", [0, -1])
+def test_wait_until_invalid_max_time(max_time):
+    test_scene = Scene()
+    with pytest.raises(ValueError, match="The max_time must be a positive number."):
+        test_scene.wait_until(lambda: True, max_time)