gfx-rs/wgpu · error

Clamp to border is not supported

Error message

Clamp to border is not supported

What it means

Raised by map_address_mode in the WebGPU (browser) backend when a sampler is created with AddressMode::ClampToBorder. The browser WebGPU API only supports ClampToEdge, Repeat, and MirrorRepeat address modes, so the backend cannot map ClampToBorder and panics. This is a backend capability limitation, not a validation error.

Source

Thrown at wgpu/src/backend/webgpu.rs:775

    match mode {
        wgt::FilterMode::Nearest => webgpu_sys::GpuFilterMode::Nearest,
        wgt::FilterMode::Linear => webgpu_sys::GpuFilterMode::Linear,
    }
}

fn map_mipmap_filter_mode(mode: wgt::MipmapFilterMode) -> webgpu_sys::GpuMipmapFilterMode {
    match mode {
        wgt::MipmapFilterMode::Nearest => webgpu_sys::GpuMipmapFilterMode::Nearest,
        wgt::MipmapFilterMode::Linear => webgpu_sys::GpuMipmapFilterMode::Linear,
    }
}

fn map_address_mode(mode: wgt::AddressMode) -> webgpu_sys::GpuAddressMode {
    match mode {
        wgt::AddressMode::ClampToEdge => webgpu_sys::GpuAddressMode::ClampToEdge,
        wgt::AddressMode::Repeat => webgpu_sys::GpuAddressMode::Repeat,
        wgt::AddressMode::MirrorRepeat => webgpu_sys::GpuAddressMode::MirrorRepeat,
        wgt::AddressMode::ClampToBorder => panic!("Clamp to border is not supported"),
    }
}

fn map_color(color: wgt::Color) -> webgpu_sys::GpuColorDict {
    webgpu_sys::GpuColorDict::new(color.a, color.b, color.g, color.r)
}

fn map_store_op(store: crate::StoreOp) -> webgpu_sys::GpuStoreOp {
    match store {
        crate::StoreOp::Store => webgpu_sys::GpuStoreOp::Store,
        crate::StoreOp::Discard => webgpu_sys::GpuStoreOp::Discard,
    }
}

fn map_map_mode(mode: crate::MapMode) -> u32 {
    match mode {
        crate::MapMode::Read => webgpu_sys::gpu_map_mode::READ,
        crate::MapMode::Write => webgpu_sys::gpu_map_mode::WRITE,

View on GitHub (pinned to 3e11ff59bf)

Solutions

1. Change the sampler's address mode to ClampToEdge, Repeat, or MirrorRepeat on web.
2. Emulate ClampToBorder in-shader: clamp UVs and manually blend with the border color at edges.
3. Pad the texture with the border color in its own pixels and use ClampToEdge to approximate the behavior.

Example fix

// before
let sampler = device.create_sampler(&wgpu::SamplerDescriptor { address_mode: wgpu::AddressMode::ClampToBorder, ..Default::default() });
// after
let sampler = device.create_sampler(&wgpu::SamplerDescriptor { address_mode: wgpu::AddressMode::ClampToEdge, ..Default::default() });

assert_ne!(address_mode, wgpu::AddressMode::ClampToBorder, "ClampToBorder unsupported on web backend");

fn is_web_safe_address_mode(m: wgpu::AddressMode) -> bool {
    matches!(m, wgpu::AddressMode::ClampToEdge | wgpu::AddressMode::Repeat | wgpu::AddressMode::MirrorRepeat)
}

When it happens

Trigger: Calling device.create_sampler with address_mode (or any of address_mode_u/v/w) set to wgpu::AddressMode::ClampToBorder on the web backend.

Common situations: Sharing sampler configuration between native and web builds; using border-color-based effects like mirrored UI padding or shadow-map comparison sampling that rely on ClampToBorder; porting native engines to WASM.

Related errors

• Web backend does not support arrays of samplers
• multi-plane textures are not supported
• found `ShaderSource::Dummy`
• Web backend does not support arrays of buffers
• Web backend does not support BINDING_INDEXING extension

AI-assisted analysis of gfx-rs/wgpu@3e11ff59bf (2026-09-03). Data as JSON: /api/errors/995c5fd5e94b1d02. Report an issue: GitHub.