bevyengine/bevy · error

Allocation didn't exist or was already prepared

Error message

Allocation didn't exist or was already prepared

What it means

Panic in MaterialBindGroupAllocator::prepare_bind_groups: an unprepared bind group listed in to_prepare had no pending allocation entry (already prepared or never allocated). Indicates allocator state bookkeeping corruption; normally unreachable.

Source

Thrown at crates/bevy_render/src/material_bind_groups.rs:2487

    /// [`Self::allocate_unprepared`]. Such bind groups will defer being
    /// prepared until the next time this method is called.
    fn prepare_bind_groups(
        &mut self,
        render_device: &RenderDevice,
        pipeline_cache: &PipelineCache,
        fallback_buffer: &FallbackBuffer,
        shader_buffer_assets: &RenderAssets<GpuShaderBuffer>,
        changed_shader_buffers: &RenderChangedShaderBuffers,
    ) {
        self.invalidate_bind_group_for_changed_shader_buffers_if_needed(changed_shader_buffers);

        for bind_group_index in mem::take(&mut self.to_prepare) {
            let Some(MaterialNonBindlessAllocatedBindGroup::Unprepared {
                bind_group: unprepared_bind_group,
                layout: bind_group_layout,
            }) = mem::take(&mut self.bind_groups[*bind_group_index as usize])
            else {
                panic!("Allocation didn't exist or was already prepared");
            };

            // Pack any `Data` into uniform buffers.
            let mut uniform_buffers = vec![];
            for (index, binding) in unprepared_bind_group.binding_resources.iter() {
                let UnpreparedBindingResource::Data(ref data_range) = *binding else {
                    continue;
                };
                let label = format!("material uniform data {}", *index);
                let uniform_buffer = render_device.create_buffer_with_data(&BufferInitDescriptor {
                    label: Some(&label),
                    contents: &unprepared_bind_group.data_buffer
                        [(data_range.start as usize)..(data_range.end as usize)],
                    usage: BufferUsages::COPY_DST | BufferUsages::UNIFORM,
                });
                uniform_buffers.push(uniform_buffer);
            }

View on GitHub (pinned to 396ca72708)

Solutions

1. Report as a Bevy engine bug with a reproducing project
2. Avoid custom sequences that prepare the same material bind group twice

When it happens

Trigger: Thrown at crates/bevy_render/src/material_bind_groups.rs:2487 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/904b557c9cb5a3bb. Report an issue: GitHub.