bevyengine/bevy · error · CubicBezierError

Unable to generate cubic curve: at least one set of control

Error message

Unable to generate cubic curve: at least one set of control points is required

What it means

CubicBezier::to_curve() errors when the spline holds no control point sets: at least one [P; 4] is required to form a segment (crates/bevy_math/src/cubic_splines/mod.rs:75-87). CubicBezier::new collects an iterator of 4-point sets, so an empty iterator yields an empty spline that cannot produce a curve.

Source

Thrown at crates/bevy_math/src/cubic_splines/mod.rs:92

    #[inline]
    fn to_curve(&self) -> Result<CubicCurve<P>, Self::Error> {
        let segments = self
            .control_points
            .iter()
            .map(|p| CubicSegment::new_bezier(*p))
            .collect_vec();

        if segments.is_empty() {
            Err(CubicBezierError)
        } else {
            Ok(CubicCurve { segments })
        }
    }
}
/// An error returned during cubic curve generation for cubic Bezier curves indicating that a
/// segment of control points was not present.
#[derive(Clone, Debug, Error)]
#[error("Unable to generate cubic curve: at least one set of control points is required")]
pub struct CubicBezierError;

/// A spline interpolated continuously between the nearest two control points, with the position and
/// velocity of the curve specified at both control points. This curve passes through all control
/// points, with the specified velocity which includes direction and parametric speed.
///
/// Useful for smooth interpolation when you know the position and velocity at two points in time,
/// such as network prediction.
///
/// ### Interpolation
///
/// The curve passes through every control point.
///
/// ### Tangency
///
/// Tangents are explicitly defined at each control point.
///
/// ### Continuity

View on GitHub (pinned to 396ca72708)

Solutions

Ensure at least one set of four control points is provided before calling to_curve().
Validate control_points is non-empty at construction time and fail loudly with context.
Log the point count where curves are generated to catch upstream data loss early.

Example fix

// before
let curve = CubicBezier::new(points).to_curve().unwrap(); // points empty -> error

// after
assert!(!points.is_empty(), "curve needs control points");
let curve = CubicBezier::new(points).to_curve()?;

Defensive patterns

Strategy: validation

Validate before calling

use bevy_math::CubicBezier;

fn build_curve<P: VectorSpace<Scalar = f32>>(points: Vec<[P; 4]>) -> Option<Result<CubicCurve<P>, CubicBezierError>> {
    if points.is_empty() {
        return None;
    }
    Some(CubicBezier::new(points).to_curve())
}

Try / catch

let curve = CubicBezier::new(points).to_curve();
match curve {
    Ok(c) => { /* sample c */ }
    Err(CubicBezierError) => { /* skip: no control point sets were provided */ }
}

Prevention

Assert non-empty control point sets where curves are authored.
Validate procedurally generated point sets before curve construction.
Log point counts at generation sites to catch emptied collections.

When it happens

Trigger: CubicBezier::new(empty_iterator).to_curve(), or building the control point list at runtime where a filter or data pipeline removed all points.

Common situations: Procedurally generated paths that end up empty (no samples passed a filter); config-driven curves with missing data; entity-driven curves where the source collection was despawned.

Related errors

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/2f91a9b744a9a662. Report an issue: GitHub.