bevyengine/bevy · error · GltfError

failed to generate morph targets: {0}

Error message

failed to generate morph targets: {0}

What it means

GltfError::MorphTarget (#[from] bevy_mesh::morph::MorphBuildError) wraps failures while building morph-target vertex data and weights: mesh.set_morph_targets (loader/mod.rs:810) and MorphWeights::new (mod.rs:1902) require each target's attributes to match the expected POSITION/NORMAL/TANGENT layout and consistent counts; mismatches error out instead of producing a broken skinned mesh.

Source

Thrown at crates/bevy_gltf/src/loader/mod.rs:131

    ImageError(#[from] TextureError),
    /// The image URI was unable to be resolved with respect to the asset path.
    #[error("invalid image uri: {0}. asset path error={1}")]
    InvalidImageUri(String, ParseAssetPathError),
    /// Failed to read bytes from an asset path.
    #[error("failed to read bytes from an asset path: {0}")]
    ReadAssetBytesError(#[from] ReadAssetBytesError),
    /// Failed to load asset from an asset path.
    #[error("failed to load asset from an asset path: {0}")]
    AssetLoadError(#[from] AssetLoadError),
    /// Missing sampler for an animation.
    #[error("Missing sampler for animation {0}")]
    #[from(ignore)]
    MissingAnimationSampler(usize),
    /// Failed to generate tangents.
    #[error("failed to generate tangents: {0}")]
    GenerateTangentsError(#[from] bevy_mesh::GenerateTangentsError),
    /// Failed to generate morph targets.
    #[error("failed to generate morph targets: {0}")]
    MorphTarget(#[from] bevy_mesh::morph::MorphBuildError),
    /// Circular children in Nodes
    #[error("GLTF model must be a tree, found cycle instead at node indices: {0:?}")]
    #[from(ignore)]
    CircularChildren(String),
    /// Failed to load a file.
    #[error("failed to load file: {0}")]
    Io(#[from] Error),
}

/// Loads glTF files with all of their data as their corresponding bevy representations.
#[derive(TypePath)]
pub struct GltfLoader {
    /// List of compressed image formats handled by the loader.
    pub supported_compressed_formats: CompressedImageFormats,
    /// Custom vertex attributes that will be recognized when loading a glTF file.
    ///
    /// Keys must be the attribute names as found in the glTF data, which must start with an underscore.

View on GitHub (pinned to 396ca72708)

Solutions

1. Re-export shape keys ensuring every target carries POSITION (+ NORMAL/TANGENT) with identical formats and counts.
2. Delete unused shape keys before export to shrink the surface for mistakes.
3. Validate morph accessors with gltf-validator (checks target attribute consistency).
4. If morphs are not needed, export without shape keys.

fn morph_targets_consistent(doc: &gltf::Document) -> bool {
    doc.meshes().flat_map(|m| m.primitives()).all(|p| {
        let base: Vec<_> = p.attributes().iter().map(|(s, _)| s.to_string()).collect();
        p.morph_targets().all(|t| t.iter().all(|(s, _)| {
            base.iter().any(|b| b == &s.to_string())
                && matches!(s, gltf::Semantic::Positions | gltf::Semantic::Normals | gltf::Semantic::Tangents)
        }))
    })
}

match err {
    GltfError::MorphTarget(e) => {
        warn!("morph targets invalid ({e:?}); re-export shape keys with full POSITION/NORMAL/TANGENT sets");
    }
    other => return Err(other.into()),
}

When it happens

Trigger: A primitive whose morph targets omit some attributes (e.g. targets with POSITION but stray formats), target attributes with differing vertex counts/formats, or weights arrays inconsistent with the number of targets.

Common situations: Shape keys exported partially from DCCs; hand-crafted morph data; mixers combining targets from different meshes; aggressive optimizers rewriting morph accessors.

Related errors

• unsupported primitive mode
• failed to generate tangents: {0}
• Too many vertex components in morph target, max is {MAX_COMP
• Bevy only supports up to {} morph targets (individual poses)
• invalid glTF file: {0}

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/600b741ad63c013c. Report an issue: GitHub.