phaser/wip/states/MainLoop.js

/**
* @author       Richard Davey <rich@photonstorm.com>
* @copyright    2016 Photon Storm Ltd.
* @license      {@link https://github.com/photonstorm/phaser/blob/master/license.txt|MIT License}
*/

// My thanks to Isaac Sukin for creating MainLoop.js, on which lots of this is based.

Phaser.State.MainLoop = function (state, framerate)
{
    /**
    * @property {Phaser.State} state
    */
    this.state = state;

    /**
    * @property {Phaser.Game} game - A reference to the currently running Game.
    */
    this.game = state.game;

    // The amount of time (in milliseconds) to simulate each time update() runs.
    this.timestep = 1000 / framerate;

    this.physicsStep = 1 / framerate;

    // The cumulative amount of in-app time that hasn't been simulated yet.
    // See the comments inside animate() for details.
    this.frameDelta = 0;

    // The timestamp in milliseconds of the last time the main loop was run.
    // Used to compute the time elapsed between frames.
    this.lastFrameTimeMs = 0;

    // An exponential moving average of the frames per second.
    this.fps = 60;

    // The timestamp (in milliseconds) of the last time the `fps` moving
    // average was updated.
    this.lastFpsUpdate = 0;

    // The number of frames delivered in the current second.
    this.framesThisSecond = 0;

    // The number of times update() is called in a given frame. This is only
    // relevant inside of animate(), but a reference is held externally so that
    // this variable is not marked for garbage collection every time the main
    // loop runs.
    this.numUpdateSteps = 0;

    // The minimum amount of time in milliseconds that must pass since the last
    // frame was executed before another frame can be executed. The
    // multiplicative inverse caps the FPS (the default of zero means there is
    // no cap).
    this.minFrameDelay = 0;

    // Whether the main loop is running.
    this.running = false;

    // `true` if `MainLoop.start()` has been called and the most recent time it
    // was called has not been followed by a call to `MainLoop.stop()`. This is
    // different than `running` because there is a delay of a few milliseconds
    // after `MainLoop.start()` is called before the application is considered
    // "running." This delay is due to waiting for the next frame.
    this.started = false;

    // Whether the simulation has fallen too far behind real time.
    // Specifically, `panic` will be set to `true` if too many updates occur in
    // one frame. This is only relevant inside of animate(), but a reference is
    // held externally so that this variable is not marked for garbage
    // collection every time the main loop runs.
    this.panic = false;
};

Phaser.State.MainLoop.prototype.constructor = Phaser.State.MainLoop;

Phaser.State.MainLoop.prototype = {

    setMaxFPS: function (fps)
    {
        if (fps === 0)
        {
            this.stop();
        }
        else
        {
            this.minFrameDelay = 1000 / fps;
        }
    },

    getMaxFPS: function ()
    {
        return 1000 / this.minFrameDelay;
    },

    resetFrameDelta: function ()
    {
        var oldFrameDelta = this.frameDelta;

        this.frameDelta = 0;

        return oldFrameDelta;
    },

    start: function ()
    {
        if (this.started)
        {
            return this;
        }

        this.started = true;
        this.running = true;

        this.lastFrameTimeMs = window.performance.now();
        this.lastFpsUpdate = window.performance.now();
        this.framesThisSecond = 0;
    },

    //  timestamp = DOMHighResTimeStamp
    step: function (timestamp)
    {
        // Throttle the frame rate (if minFrameDelay is set to a non-zero value by
        // `MainLoop.setMaxAllowedFPS()`).
        if (timestamp < this.lastFrameTimeMs + this.minFrameDelay)
        {
            return;
        }

        // frameDelta is the cumulative amount of in-app time that hasn't been
        // simulated yet. Add the time since the last frame. We need to track total
        // not-yet-simulated time (as opposed to just the time elapsed since the
        // last frame) because not all actually elapsed time is guaranteed to be
        // simulated each frame. See the comments below for details.
        this.frameDelta += timestamp - this.lastFrameTimeMs;
        this.lastFrameTimeMs = timestamp;

        // Run any updates that are not dependent on time in the simulation.

        //  Here we'll need to run things like tween.update, input.update, etc.
        this.state.sys.begin(timestamp, this.frameDelta);

        // Update the estimate of the frame rate, `fps`. Every second, the number
        // of frames that occurred in that second are included in an exponential
        // moving average of all frames per second, with an alpha of 0.25. This
        // means that more recent seconds affect the estimated frame rate more than
        // older seconds.
        if (timestamp > this.lastFpsUpdate + 1000)
        {
            // Compute the new exponential moving average with an alpha of 0.25.
            // Using constants inline is okay here.
            this.fps = 0.25 * this.framesThisSecond + 0.75 * this.fps;

            this.lastFpsUpdate = timestamp;
            this.framesThisSecond = 0;
        }

        this.framesThisSecond++;

        this.numUpdateSteps = 0;

        var step = this.timestep;

        while (this.frameDelta >= step)
        {
            // this.update(this.timestep);

            this.state.sys.update(step, this.physicsStep);

            for (var c = 0; c < this.state.sys.children.list.length; c++)
            {
                var child = this.state.sys.children.list[c];

                if (child.exists)
                {
                    child.update(step);
                }
            }

            //  Dev level callback
            this.state.update(step);

            this.frameDelta -= this.timestep;

            if (++this.numUpdateSteps >= 240)
            {
                this.panic = true;
                break;
            }
        }

        this.state.sys.preRender();

        this.state.sys.updates.start();

        if (this.state.settings.visible && this.state.sys.color.alpha !== 0 && this.state.sys.children.list.length > 0)
        {
            this.game.renderer.render(this.state, this.frameDelta / this.timestep);
        }

        this.state.sys.updates.stop();

        // Run any updates that are not dependent on time in the simulation.
        this.state.sys.end(this.fps, this.panic);

        this.panic = false;
    },

    /*
    update: function (timestep)
    {
        this.state.sys.update(timestep);

        var c;
        var child;

        for (var c = 0; c < this.state.sys.children.list.length; c++)
        {
            var child = this.state.sys.children.list[c];

            if (child.exists)
            {
                child.update(timestep);
            }
        }

        //  Dev level callback
        this.state.update(timestep);

        for (c = 0; c < this.state.sys.children.list.length; c++)
        {
            var child = this.state.sys.children.list[c];

            if (child.exists)
            {
                child.update(timestep);
            }
        }
    },
    */

    stop: function ()
    {
        this.running = false;
        this.started = false;

        return this;
    }

};