/**
 * WebGPU backend for `<r-glass rim>` — the exact same shape-only SDF rim +
 * chromatic fringe as the WebGL backend in `rim.ts`, reimplemented in WGSL.
 * See the module doc in `rim.ts` for what this draws and why it never
 * samples the backdrop; this file is purely an alternate rendering backend
 * for the identical effect, not a different one.
 *
 * WHY THIS EXISTS, GIVEN THE WEBGL PATH ALREADY WORKS EVERYWHERE:
 * It doesn't make this draw any faster. A single draw call, reissued only on
 * resize/radius change, has no per-frame or many-draw-call overhead for
 * WebGPU's command-buffer model to amortize, and the GPU-side shader work (a
 * handful of distance-field evaluations over a thin band of pixels) is
 * microseconds either way — the bottleneck for this workload was never the
 * choice of API. This backend exists because it was explicitly requested,
 * not because it measurably helps this effect; if `rim` ever grows into a
 * heavier multi-pass effect (real per-frame refraction, multiple blur
 * passes), that's the scenario where WebGPU's model would actually start to
 * matter.
 *
 * WHY IT'S A SEPARATE, OPTIONAL UPGRADE INSTEAD OF REPLACING WEBGL:
 * `GPUAdapter`/`GPUDevice` negotiation (`requestAdapter`/`requestDevice`) is
 * asynchronous — unlike `canvas.getContext('webgl')`, which returns
 * synchronously. Blocking the rim's first appearance on that Promise would
 * make an optional decorative layer show up later than the WebGL path does
 * today, for a visually identical result — a real regression for zero gain.
 * So `createRimRenderer` in `rim.ts` always shows the WebGL canvas first and
 * only swaps to this backend if/when the negotiation here resolves.
 */
export interface RimBackend {
    /** Draws once at the given backing-store size (already dpr-scaled) plus CSS-px radius and dpr. */
    draw(width: number, height: number, radius: number, dpr: number): void;
    /** Frees the GPU device — browsers cap how many WebGPU/WebGL contexts can be live at once. */
    destroy(): void;
}
/**
 * Negotiates a WebGPU device and configures `canvas` for it. Resolves to
 * `null` — never rejects — if WebGPU isn't present, adapter/device
 * negotiation fails, or the canvas context can't be configured. Every one of
 * those cases means the same thing to the caller: keep showing the WebGL rim.
 */
export declare function createWebGpuRim(canvas: HTMLCanvasElement): Promise<RimBackend | null>;