bevyengine/bevy · error · MeshTrianglesError

Source mesh does not have primitive topology TriangleList or

Error message

Source mesh does not have primitive topology TriangleList or TriangleStrip

What it means

Mesh::triangles() (crates/bevy_mesh/src/mesh.rs:2540) can only produce Triangle3d faces from meshes whose primitive_topology is TriangleList or TriangleStrip. Any other topology (PointList, LineList, LineStrip) reaches the fallback arm and returns MeshTrianglesError::WrongTopology.

Source

Thrown at crates/bevy_mesh/src/index.rs:68

#[derive(Debug, Error)]
pub enum MeshWindingInvertError {
    /// This error occurs when you try to invert the winding for a mesh with [`PrimitiveTopology::PointList`](super::PrimitiveTopology::PointList).
    #[error("Mesh winding inversion does not work for primitive topology `PointList`")]
    WrongTopology,

    /// This error occurs when you try to invert the winding for a mesh with
    /// * [`PrimitiveTopology::TriangleList`](super::PrimitiveTopology::TriangleList), but the indices are not in chunks of 3.
    /// * [`PrimitiveTopology::LineList`](super::PrimitiveTopology::LineList), but the indices are not in chunks of 2.
    #[error("Indices weren't in chunks according to topology")]
    AbruptIndicesEnd,
    #[error("Mesh access error: {0}")]
    MeshAccessError(#[from] MeshAccessError),
}

/// An error that occurred while trying to extract a collection of triangles from a [`Mesh`](super::Mesh).
#[derive(Debug, Error)]
pub enum MeshTrianglesError {
    #[error("Source mesh does not have primitive topology TriangleList or TriangleStrip")]
    WrongTopology,

    #[error("Source mesh position data is not Float32x3")]
    PositionsFormat,

    #[error("Face index data references vertices that do not exist")]
    BadIndices,
    #[error("mesh access error: {0}")]
    MeshAccessError(#[from] MeshAccessError),
}

/// An array of indices into the [`VertexAttributeValues`](super::VertexAttributeValues) for a mesh.
///
/// It describes the order in which the vertex attributes should be joined into faces.
#[derive(Debug, Clone, Reflect, PartialEq)]
#[reflect(Clone)]
#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
pub enum Indices {

View on GitHub (pinned to 396ca72708)

Solutions

1. Check mesh.primitive_topology() is TriangleList or TriangleStrip before calling triangles()
2. Skip non-triangle meshes in generic iteration code
3. Rebuild the mesh with a triangle topology if triangle data was actually expected

Example fix

// before
let tris: Vec<Triangle3d> = mesh.triangles()?.collect(); // Err(WrongTopology) on lines/points

// after
let tris = if matches!(
    mesh.primitive_topology(),
    PrimitiveTopology::TriangleList | PrimitiveTopology::TriangleStrip
) {
    mesh.triangles()?.collect::<Vec<_>>()
} else {
    Vec::new()
};

fn has_triangle_topology(mesh: &Mesh) -> bool {
    matches!(
        mesh.primitive_topology(),
        PrimitiveTopology::TriangleList | PrimitiveTopology::TriangleStrip
    )
}

if has_triangle_topology(&mesh) {
    let tris: Vec<_> = mesh.triangles()?.collect();
}

match mesh.triangles() {
    Ok(iter) => { /* iterate Triangle3d faces */ }
    Err(MeshTrianglesError::WrongTopology) => { /* skip non-triangle meshes */ }
    Err(other) => { /* positions/access errors */ }
}

When it happens

Trigger: mesh.triangles() or mesh.triangles_mut() on a mesh whose primitive_topology() is PointList, LineList or LineStrip.

Common situations: Physics or raytracing code that iterates triangles of every mesh, including particle or line meshes; UI/debug pipelines fed with non-triangle meshes; imported assets whose topology differs from the loader expectation.

Related errors

• Mesh winding inversion does not work for primitive topology
• Source mesh position data is not Float32x3
• Face index data references vertices that do not exist
• mesh access error: {0}
• cannot convert VertexAttributeValues::{variant} to {into}

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/cdfb40bcf6260ccc. Report an issue: GitHub.