bevyengine/bevy · error · InsufficientDataError

Not enough data to build curve: needed at least {expected} c

Error message

Not enough data to build curve: needed at least {expected} control points but was only given {given}

What it means

InsufficientDataError is the error type of CubicGenerator::to_curve / CyclicCubicGenerator::to_curve_cyclic. It reports `expected` = the minimum point count for that spline and `given` = what you supplied. Point-interpolation splines (LinearSpline, CubicBezier point interpolation, Hermite) need at least 2 points; control-point splines (CubicBezierSpline with control points, CubicBSpline) need at least 4.

Source

Thrown at crates/bevy_math/src/cubic_splines/mod.rs:906

            .map(|(&a, &b)| CubicSegment {
                coeff: [a, b - a, P::default(), P::default()],
            })
            .collect_vec();

        if segments.is_empty() {
            Err(InsufficientDataError {
                expected: 2,
                given: self.points.len(),
            })
        } else {
            Ok(CubicCurve { segments })
        }
    }
}

/// An error indicating that a spline construction didn't have enough control points to generate a curve.
#[derive(Clone, Debug, Error)]
#[error("Not enough data to build curve: needed at least {expected} control points but was only given {given}")]
pub struct InsufficientDataError {
    expected: usize,
    given: usize,
}

/// Implement this on cubic splines that can generate a cubic curve from their spline parameters.
#[cfg(feature = "alloc")]
pub trait CubicGenerator<P: VectorSpace> {
    /// An error type indicating why construction might fail.
    type Error;

    /// Build a [`CubicCurve`] by computing the interpolation coefficients for each curve segment.
    fn to_curve(&self) -> Result<CubicCurve<P>, Self::Error>;
}

/// Implement this on cubic splines that can generate a cyclic cubic curve from their spline parameters.
///
/// This makes sense only when the control data can be interpreted cyclically.

View on GitHub (pinned to 396ca72708)

Solutions

Check the error message: `expected` tells you the exact minimum for the spline type you used; supply at least that many points.
Branch at runtime: skip curve creation or fall back to a constant/linear path when points.len() < expected.
For data-driven splines, validate keyframe counts at asset load time and reject with a descriptive asset error instead of failing mid-system.

Example fix

// before
let spline = LinearSpline::new(vec![start]);
let curve = spline.to_curve()?; // InsufficientDataError { expected: 2, given: 1 }

// after
let spline = LinearSpline::new(points.clone());
let curve = if points.len() >= 2 {
    Some(spline.to_curve()?)
} else {
    None // or hold position / teleport to the single point
};

Defensive patterns

Strategy: try-catch

Validate before calling

const MIN_POINTS: usize = 2; // 4 for CubicBSpline / control-point CubicBezierSpline
if spline_points.len() >= MIN_POINTS {
    let curve = spline.to_curve()?;
}

Try / catch

let curve = match spline.to_curve() {
    Ok(curve) => curve,
    Err(InsufficientDataError { expected, given }) => {
        warn!("path needs {expected} points, got {given}; holding position");
        return Ok(()); // skip this frame rather than crash
    }
};

Prevention

Check the docs of each spline type for its minimum point count before building it.
Validate point counts at asset/entity spawn time, not inside per-frame systems.
Keep a fallback behavior (hold position, straight line) for degenerate point lists.

When it happens

Trigger: Calling to_curve() (or to_curve_cyclic()) on a spline built from fewer points than its minimum: LinearSpline::new(vec![p0]).to_curve(), CubicBezierSpline::new().add_control_points([a,b,c]).to_curve() with 3 of 4, CubicBSpline with 3 points, Hermite spline with a single point.

Common situations: Runtime-generated trajectories that can degenerate to one point; editor tools where the user has clicked only one point; animation keyframe lists loaded from data with a missing entry; tests with tiny fixtures.

Related errors

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/6aaea0d1b26e9b0f. Report an issue: GitHub.