////  RenderEventHandler.h////  Created by Bradley Austin Davis on 29/6/2018.//  Copyright 2018 High Fidelity, Inc.////  Distributed under the Apache License, Version 2.0.//  See the accompanying file LICENSE or http://www.apache.org/licenses/LICENSE-2.0.html//#ifndef hifi_RenderEventHandler_h#define hifi_RenderEventHandler_h #include <functional>#include <QEvent>#include <QElapsedTimer>#include "gl/OffscreenGLCanvas.h" enum ApplicationEvent {    // Execute a lambda function    Lambda = QEvent::User + 1,    // Trigger the next render    Render,    // Trigger the next idle    Idle,}; /** * This class does not handle actual rendering, it just generates Frame objects and submits them to be rendered * on the Present thread. */class RenderEventHandler : public QObject {    using Parent = QObject;    Q_OBJECTpublic:    using CheckCall = std::function <bool()>;    using RenderCall = std::function <void()>;     /**     * Function that gets called to check if given Frame object creation event should run or should be skipped.     * Can be used to throttle rate at which Frame objects are generated..     */    CheckCall _checkCall;     /**     * Function that generates new Frame object and submits it to display plugin to be rendered on Present thread.     */    RenderCall _renderCall;     /**     *     * @param checkCall     * @param renderCall     */    RenderEventHandler(CheckCall checkCall, RenderCall renderCall);     /**     * Time at which last Frame object was generated.     * Can be used for throttling by `GraphicsEngine::shouldPaint`.     */    QElapsedTimer _lastTimeRendered;     /**     * Frame object creation event is in progress currently or the thread is paused.     * Set to `false` after the render event finishes.     * Set to `true` in `GraphicsEngine::checkPendingRenderEvent`.     */    std::atomic<bool> _pendingRenderEvent{ true };     /**     * Processing render events is initially paused, and is resumed during the startup process using this call.     */    void resumeThread(); private:    /**     * Initialize the thread on which Frame objects will be generated.     * Thread is called Render thread, but does not do rendering.     */    void initialize();     /**     * Generate and a new Frame object and submit it to display plugin to be rendered later on a separate thread.     */    void render();     /**     * Qt event handler. Handles "render" event (which generates a Frame object but does not render) posted my main application.     * @param event Qt event.     * @return True if the event was processed.     */    bool event(QEvent* event) override;}; #endif // #include hifi_RenderEventHandler_h