import { Context } from './context';
export declare class ExtensionsHash {
    protected static readonly WEBGL_BACKENDS: Array<string>;
    protected static readonly WEBGL_EXTENSIONS_BY_BACKEND: Map<number, string[]>;
    /**
     * All known WebGL extensions (regardless of WebGL version). When new extensions become known, a new internal
     * version has to be created, comprising all extensions again (some removed, some added w.r.t. previous versions).
     */
    protected static readonly EXTENSIONS_BY_VERSION: Map<number, string[]>;
    /**
     * Hash versioning is used to account for future, yet unknown/unpublished extensions while maintaining support for
     * existing hashes.
     */
    protected static readonly LATEST_VERSION = 0;
    protected static readonly BASE64_ALPHABET = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-+";
    /**
     * Encodes a number of bitfield semantics (of 6 bits) into a base64 character.
     * @param base64 - Bitfield of 6 bits (as number).
     */
    protected static encode64(bitfield: number): string;
    /**
     * Decodes a single base64 encoded character to a number of bitfield semantics.
     * @param base64 - Single base64 encoded character (string).
     */
    protected static decode64(base64: string): number;
    /**
     * Generates a hash that encodes the contexts webgl backend and extension support. This is intended to be queried
     * whenever support for a given context on a foreign client is due. The hash can be used as masquerade input.
     * @param backend - WebGL backend: 'webgl1' or 'webgl2'.
     * @param supported - Array of supported extensions to be encoded.
     */
    static encode(backend: Context.BackendType, supported: Array<string>): string;
    /**
     * Decodes a hash into a WebGL backend and supported extensions.
     * @param hash - Versioned extension hash.
     * @returns - Tuple of webgl backend and an array of extensions.
     */
    static decode(hash: string): [string, Array<string>];
    /**
     * For a given set of extensions, this generates the complementary set of extensions for a given backend.
     * @param backend - WebGL backend: 'webgl1' or 'webgl2'.
     * @param extensions - Array of extensions to be complemented to all extensions available to the backend.
     */
    static complement(backend: string, extensions: Array<string>): Array<string>;
}