Fix scene skipping for config.upto_animation_number (-n flag in C…

…LI) set to 0 to end after first animation (#4013)

* make checks involving from/upto_animation_number more explicit

* add test for flag -n 0,0 for only rendering first animation

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Aarush Deshpande <[email protected]>

manim/renderer/cairo_renderer.py

@@ -252,13 +252,13 @@ def update_skipping_status(self):
         if config["save_last_frame"]:
             self.skip_animations = True
         if (
-            config["from_animation_number"]
-            and self.num_plays < config["from_animation_number"]
+            config.from_animation_number > 0
+            and self.num_plays < config.from_animation_number
         ):
             self.skip_animations = True
         if (
-            config["upto_animation_number"]
-            and self.num_plays > config["upto_animation_number"]
+            config.upto_animation_number >= 0
+            and self.num_plays > config.upto_animation_number
         ):
             self.skip_animations = True
             raise EndSceneEarlyException()

manim/renderer/opengl_renderer.py

@@ -400,13 +400,13 @@ def update_skipping_status(self):
         if self.file_writer.sections[-1].skip_animations:
             self.skip_animations = True
         if (
-            config["from_animation_number"]
-            and self.num_plays < config["from_animation_number"]
+            config.from_animation_number > 0
+            and self.num_plays < config.from_animation_number
         ):
             self.skip_animations = True
         if (
-            config["upto_animation_number"]
-            and self.num_plays > config["upto_animation_number"]
+            config.upto_animation_number >= 0
+            and self.num_plays > config.upto_animation_number
         ):
             self.skip_animations = True
             raise EndSceneEarlyException()

tests/test_config.py

@@ -244,3 +244,24 @@ def test_tex_template_file(tmp_path):
 
     assert Path(custom_config.tex_template_file) == tex_file
     assert custom_config.tex_template.body == "Hello World!"
+
+
+def test_from_to_animations_only_first_animation(config):
+    config: ManimConfig
+    config.from_animation_number = 0
+    config.upto_animation_number = 0
+
+    class SceneWithTwoAnimations(Scene):
+        def construct(self):
+            self.after_first_animation = False
+            s = Square()
+            self.add(s)
+            self.play(s.animate.scale(2))
+            self.renderer.update_skipping_status()
+            self.after_first_animation = True
+            self.play(s.animate.scale(2))
+
+    scene = SceneWithTwoAnimations()
+    scene.render()
+
+    assert scene.after_first_animation is False