3b1b/manim · error · ValueError

At least 2 mobjects needed for Intersection.

Error message

At least 2 mobjects needed for Intersection.

What it means

ValueError raised in Intersection.__init__ (manimlib/mobject/boolean_ops.py:81). Intersection folds pairwise skia-pathops intersection over the operand list starting from vmobjects[0] and vmobjects[1], so at least two mobjects are structurally required; with fewer than two there is nothing to intersect.

Source

Thrown at manimlib/mobject/boolean_ops.py:81

        _convert_skia_path_to_vmobject(outpen, self)


class Difference(VMobject):
    def __init__(self, subject: VMobject, clip: VMobject, **kwargs):
        super().__init__(**kwargs)
        outpen = pathops.Path()
        pathops.difference(
            [_convert_vmobject_to_skia_path(subject)],
            [_convert_vmobject_to_skia_path(clip)],
            outpen.getPen(),
        )
        _convert_skia_path_to_vmobject(outpen, self)


class Intersection(VMobject):
    def __init__(self, *vmobjects: VMobject, **kwargs):
        if len(vmobjects) < 2:
            raise ValueError("At least 2 mobjects needed for Intersection.")
        super().__init__(**kwargs)
        outpen = pathops.Path()
        pathops.intersection(
            [_convert_vmobject_to_skia_path(vmobjects[0])],
            [_convert_vmobject_to_skia_path(vmobjects[1])],
            outpen.getPen(),
        )
        new_outpen = outpen
        for _i in range(2, len(vmobjects)):
            new_outpen = pathops.Path()
            pathops.intersection(
                [outpen],
                [_convert_vmobject_to_skia_path(vmobjects[_i])],
                new_outpen.getPen(),
            )
            outpen = new_outpen
        _convert_skia_path_to_vmobject(outpen, self)

View on GitHub (pinned to dee01804d4)

Solutions

1. Pass at least two VMobjects: Intersection(mob_a, mob_b, mob_c)
2. Pre-check the splatted collection length before calling
3. For a single shape use the shape itself; for zero shapes decide on an Empty/VGroup fallback

Example fix

# before
overlap = Intersection(*regions)  # raises if len(regions) < 2

# after
assert len(regions) >= 2, "Intersection needs >= 2 mobjects"
overlap = Intersection(*regions)

if len(regions) < 2:
    raise ValueError(f"Intersection needs >= 2 mobjects, got {len(regions)}")
overlap = Intersection(*regions)

def is_intersection_ready(mobs: list) -> bool:
    return len(mobs) >= 2

When it happens

Trigger: Intersection(one_mob), Intersection(), or Intersection(*groups) where the splat yields fewer than two mobjects (e.g. an empty VGroup spread).

Common situations: Calling Intersection(*vg) where vg was filtered or sliced to <2 elements; animations where one operand is conditionally removed; copy-paste from Union example with a single argument.

Related errors

• At least 2 mobjects needed for Union.
• At least 2 mobjects needed for Exclusion.
• Unsupported: {path_verb}
• Invalid input sample type
• Mobject cannot contain self

AI-assisted analysis of 3b1b/manim@dee01804d4 (2026-08-14). Data as JSON: /api/errors/c5d031ee860e1889. Report an issue: GitHub.