Fix code transform animation

manim/mobject/text/__init__.py

@@ -7,6 +7,7 @@
     :toctree: ../reference
 
     ~code_mobject
+    ~code_transform
     ~numbers
     ~tex_mobject
     ~text_mobject

manim/mobject/text/code_transform.py

@@ -0,0 +1,97 @@
+from __future__ import annotations
+
+from manim import *
+
+
+def find_line_matches(before: Code, after: Code):
+    before_lines = [
+        line.lstrip() if line.strip() != "" else None
+        for line in before.code_string.splitlines()
+    ]
+    after_lines = [
+        line.lstrip() if line.strip() != "" else None
+        for line in after.code_string.splitlines()
+    ]
+
+    matches = []
+
+    for i, b_line in enumerate(before_lines):
+        if b_line is None:
+            continue
+        for j, a_line in enumerate(after_lines):
+            if a_line is not None and b_line == a_line:
+                matches.append((i, j))
+                before_lines[i] = None
+                after_lines[j] = None
+                break
+
+    deletions = []
+    for i, line in enumerate(before_lines):
+        if before_lines[i] is not None:
+            deletions.append((i, len(line)))
+
+    additions = []
+    for j, line in enumerate(after_lines):
+        if after_lines[j] is not None:
+            additions.append((j, len(line)))
+
+    return matches, deletions, additions
+
+
+class CodeTransform(AnimationGroup):
+    """
+    An animation that smoothly transitions between two Code objects.
+
+    PARAMETERS
+    ----------
+    before : Code
+        The initial Code object.
+    after : Code
+        The target Code object after the transition.
+    """
+
+    def __init__(self, before: Code, after: Code, **kwargs):
+        matches, deletions, additions = find_line_matches(before, after)
+
+        transform_pairs = [(before.code[i], after.code[j]) for i, j in matches]
+
+        delete_lines = [before.code[i] for i, _ in deletions]
+
+        add_lines = [after.code[j] for j, _ in additions]
+
+        animations = []
+
+        if hasattr(before, "background_mobject") and hasattr(
+            after, "background_mobject"
+        ):
+            animations.append(
+                Transform(before.background_mobject, after.background_mobject)
+            )
+
+        if hasattr(before, "line_numbers") and hasattr(after, "line_numbers"):
+            animations.append(Transform(before.line_numbers, after.line_numbers))
+
+        if delete_lines:
+            animations.append(FadeOut(*delete_lines))
+
+        if transform_pairs:
+            animations.append(
+                LaggedStart(
+                    *[
+                        Transform(before_line, after_line)
+                        for before_line, after_line in transform_pairs
+                    ]
+                )
+            )
+
+        if add_lines:
+            animations.append(FadeIn(*add_lines))
+
+        super().__init__(
+            *animations,
+            group=None,
+            run_time=None,
+            rate_func=linear,
+            lag_ratio=0.0,
+            **kwargs,
+        )

manim/utils/file_ops.py

@@ -198,7 +198,7 @@ def open_file(file_path: Path, in_browser: bool = False) -> None:
     if current_os == "Windows":
         # The method os.startfile is only available in Windows,
         # ignoring type error caused by this.
-        os.startfile(file_path if not in_browser else file_path.parent)  # type: ignore[attr-defined]
+        os.startfile(file_path if not in_browser else file_path.parent)
     else:
         if current_os == "Linux":
             commands = ["xdg-open"]

tests/test_graphical_units/test_code_transform.py

@@ -0,0 +1,58 @@
+from manim import *
+from manim.mobject.text.code_transform import CodeTransform
+from manim.utils.testing.frames_comparison import frames_comparison
+
+__module_test__ = "code_transform"
+
+
+@frames_comparison
+def test_code_transform(scene):
+    before_code = """from manim import *
+
+class Animation(Scene):
+    def construct(self):
+
+        square = Square(side_length=2.0, color=RED)
+        square.shift(LEFT * 2)
+
+        self.play(Create(square))
+        self.wait()
+"""
+
+    after_code = """from manim import *
+
+class Animation(Scene):
+    def construct(self):
+
+        circle = Circle(radius=1.0, color=BLUE)
+        circle.shift(RIGHT * 2)
+
+        square = Square(side_length=2.0, color=RED)
+        square.shift(LEFT * 2)
+
+        self.play(Create(circle))
+        self.wait()
+"""
+
+    before = Code(
+        code=before_code,
+        tab_width=4,
+        background="window",
+        language="Python",
+        font="Monospace",
+        style="one-dark",
+        line_spacing=1,
+    ).scale(0.8)
+
+    after = Code(
+        code=after_code,
+        tab_width=4,
+        background="window",
+        language="Python",
+        font="Monospace",
+        style="one-dark",
+        line_spacing=1,
+    ).scale(0.8)
+
+    scene.add(before)
+    scene.play(CodeTransform(before, after))