import type { Nullable, int } from "../../types";
import { _TimeToken } from "../../Instrumentation/timeToken";
import { PerfCounter } from "../../Misc/perfCounter";
import type { Observer } from "../../Misc/observable";
import type { AbstractEngine } from "../abstractEngine";
import "../AbstractEngine/abstractEngine.query";
declare module "../../Engines/engine" {
    interface Engine {
        /**
         * Starts a time query (used to measure time spent by the GPU on a specific frame)
         * Please note that only one query can be issued at a time
         * @returns a time token used to track the time span
         */
        startTimeQuery(): Nullable<_TimeToken>;
        /**
         * Ends a time query
         * @param token defines the token used to measure the time span
         * @returns the time spent (in ns)
         */
        endTimeQuery(token: _TimeToken): int;
        /** @internal */
        _currentNonTimestampToken: Nullable<_TimeToken>;
        /** @internal */
        _captureGPUFrameTime: boolean;
        /** @internal */
        _gpuFrameTimeToken: Nullable<_TimeToken>;
        /** @internal */
        _gpuFrameTime: PerfCounter;
        /** @internal */
        _onBeginFrameObserver: Nullable<Observer<AbstractEngine>>;
        /** @internal */
        _onEndFrameObserver: Nullable<Observer<AbstractEngine>>;
        /** @internal */
        _createTimeQuery(): Nullable<WebGLQuery>;
        /** @internal */
        _deleteTimeQuery(query: WebGLQuery): void;
        /** @internal */
        _getGlAlgorithmType(algorithmType: number): number;
        /** @internal */
        _getTimeQueryResult(query: WebGLQuery): any;
        /** @internal */
        _getTimeQueryAvailability(query: WebGLQuery): any;
    }
}