bevyengine/bevy · error · MeshTrianglesError

mesh access error: {0}

Error message

mesh access error: {0}

What it means

MeshTrianglesError::MeshAccessError is the #[from] wrapper around MeshAccessError inside triangle extraction. triangles() calls try_attribute and try_indices, which fail with ExtractedToRenderWorld when the mesh's CPU-side vertex/index data has been moved to the RenderWorld because asset_usage excludes MAIN_WORLD.

Source

Thrown at crates/bevy_mesh/src/index.rs:76

    /// * [`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 {
    U16(Vec<u16>),
    U32(Vec<u32>),
}

impl Indices {
    /// Returns an iterator over the indices.
    pub fn iter(&self) -> impl Iterator<Item = usize> + '_ {
        match self {

View on GitHub (pinned to 396ca72708)

Solutions

1. Set mesh.asset_usage to include RenderAssetUsages::MAIN_WORLD alongside RENDER_WORLD
2. Read triangle data before the mesh asset is rendered/extracted
3. Keep a separate CPU-side copy of geometry for physics/picking

Example fix

// before
mesh.asset_usage = RenderAssetUsages::RENDER_WORLD;
let tris: Vec<Triangle3d> = mesh.triangles()?.collect(); // Err(ExtractedToRenderWorld)

// after
mesh.asset_usage = RenderAssetUsages::MAIN_WORLD | RenderAssetUsages::RENDER_WORLD;
let tris: Vec<Triangle3d> = mesh.triangles()?.collect();

fn mesh_readable_on_cpu(mesh: &Mesh) -> bool {
    mesh.asset_usage.contains(RenderAssetUsages::MAIN_WORLD)
}

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

match mesh.triangles() {
    Ok(iter) => { /* use triangles */ }
    Err(MeshTrianglesError::MeshAccessError(
        MeshAccessError::ExtractedToRenderWorld,
    )) => { /* use a CPU-side copy of the geometry instead */ }
    Err(other) => { /* topology / format / index errors */ }
}

When it happens

Trigger: Calling mesh.triangles() on a mesh whose asset_usage is RenderAssetUsages::RENDER_WORLD only, after the render world has extracted the data.

Common situations: Runtime collision or picking systems reading triangles of memory-optimized meshes; mesh inspection tools running after extraction; assets shared between rendering and CPU physics without MAIN_WORLD.

Related errors

• Mesh access error: {0}
• The mesh vertex/index data has been extracted to the RenderW
• Source mesh does not have primitive topology TriangleList or
• Source mesh position data is not Float32x3
• Face index data references vertices that do not exist

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/29ebfc292da72df8. Report an issue: GitHub.