import settings from '../settings';
import { UPDATE_PRIORITY } from '../const';
import TickerListener from './TickerListener';
/**
* A Ticker class that runs an update loop that other objects listen to.
* This class is composed around listeners
* meant for execution on the next requested animation frame.
* Animation frames are requested only when necessary,
* e.g. When the ticker is started and the emitter has listeners.
*
* @class
* @memberof PIXI.ticker
*/
export default class Ticker
{
/**
*
*/
constructor()
{
/**
* The first listener. All new listeners added are chained on this.
* @private
* @type {TickerListener}
*/
this._head = new TickerListener(null, null, Infinity);
/**
* Internal current frame request ID
* @private
*/
this._requestId = null;
/**
* Internal value managed by minFPS property setter and getter.
* This is the maximum allowed milliseconds between updates.
* @private
*/
this._maxElapsedMS = 100;
/**
* Whether or not this ticker should invoke the method
* {@link PIXI.ticker.Ticker#start} automatically
* when a listener is added.
*
* @member {boolean}
* @default false
*/
this.autoStart = false;
/**
* Scalar time value from last frame to this frame.
* This value is capped by setting {@link PIXI.ticker.Ticker#minFPS}
* and is scaled with {@link PIXI.ticker.Ticker#speed}.
* **Note:** The cap may be exceeded by scaling.
*
* @member {number}
* @default 1
*/
this.deltaTime = 1;
/**
* Time elapsed in milliseconds from last frame to this frame.
* Opposed to what the scalar {@link PIXI.ticker.Ticker#deltaTime}
* is based, this value is neither capped nor scaled.
* If the platform supports DOMHighResTimeStamp,
* this value will have a precision of 1 µs.
* Defaults to target frame time
*
* @member {number}
* @default 16.66
*/
this.elapsedMS = 1 / settings.TARGET_FPMS;
/**
* The last time {@link PIXI.ticker.Ticker#update} was invoked.
* This value is also reset internally outside of invoking
* update, but only when a new animation frame is requested.
* If the platform supports DOMHighResTimeStamp,
* this value will have a precision of 1 µs.
*
* @member {number}
* @default -1
*/
this.lastTime = -1;
/**
* Factor of current {@link PIXI.ticker.Ticker#deltaTime}.
* @example
* // Scales ticker.deltaTime to what would be
* // the equivalent of approximately 120 FPS
* ticker.speed = 2;
*
* @member {number}
* @default 1
*/
this.speed = 1;
/**
* Whether or not this ticker has been started.
* `true` if {@link PIXI.ticker.Ticker#start} has been called.
* `false` if {@link PIXI.ticker.Ticker#stop} has been called.
* While `false`, this value may change to `true` in the
* event of {@link PIXI.ticker.Ticker#autoStart} being `true`
* and a listener is added.
*
* @member {boolean}
* @default false
*/
this.started = false;
/**
* Internal tick method bound to ticker instance.
* This is because in early 2015, Function.bind
* is still 60% slower in high performance scenarios.
* Also separating frame requests from update method
* so listeners may be called at any time and with
* any animation API, just invoke ticker.update(time).
*
* @private
* @param {number} time - Time since last tick.
*/
this._tick = (time) =>
{
this._requestId = null;
if (this.started)
{
// Invoke listeners now
this.update(time);
// Listener side effects may have modified ticker state.
if (this.started && this._requestId === null && this._head.next)
{
this._requestId = requestAnimationFrame(this._tick);
}
}
};
}
/**
* Conditionally requests a new animation frame.
* If a frame has not already been requested, and if the internal
* emitter has listeners, a new frame is requested.
*
* @private
*/
_requestIfNeeded()
{
if (this._requestId === null && this._head.next)
{
// ensure callbacks get correct delta
this.lastTime = performance.now();
this._requestId = requestAnimationFrame(this._tick);
}
}
/**
* Conditionally cancels a pending animation frame.
*
* @private
*/
_cancelIfNeeded()
{
if (this._requestId !== null)
{
cancelAnimationFrame(this._requestId);
this._requestId = null;
}
}
/**
* Conditionally requests a new animation frame.
* If the ticker has been started it checks if a frame has not already
* been requested, and if the internal emitter has listeners. If these
* conditions are met, a new frame is requested. If the ticker has not
* been started, but autoStart is `true`, then the ticker starts now,
* and continues with the previous conditions to request a new frame.
*
* @private
*/
_startIfPossible()
{
if (this.started)
{
this._requestIfNeeded();
}
else if (this.autoStart)
{
this.start();
}
}
/**
* Register a handler for tick events. Calls continuously unless
* it is removed or the ticker is stopped.
*
* @param {Function} fn - The listener function to be added for updates
* @param {Function} [context] - The listener context
* @param {number} [priority=PIXI.UPDATE_PRIORITY.NORMAL] - The priority for emitting
* @returns {PIXI.ticker.Ticker} This instance of a ticker
*/
add(fn, context, priority = UPDATE_PRIORITY.NORMAL)
{
return this._addListener(new TickerListener(fn, context, priority));
}
/**
* Add a handler for the tick event which is only execute once.
*
* @param {Function} fn - The listener function to be added for one update
* @param {Function} [context] - The listener context
* @param {number} [priority=PIXI.UPDATE_PRIORITY.NORMAL] - The priority for emitting
* @returns {PIXI.ticker.Ticker} This instance of a ticker
*/
addOnce(fn, context, priority = UPDATE_PRIORITY.NORMAL)
{
return this._addListener(new TickerListener(fn, context, priority, true));
}
/**
* Internally adds the event handler so that it can be sorted by priority.
* Priority allows certain handler (user, AnimatedSprite, Interaction) to be run
* before the rendering.
*
* @private
* @param {TickerListener} listener - Current listener being added.
* @returns {PIXI.ticker.Ticker} This instance of a ticker
*/
_addListener(listener)
{
// For attaching to head
let current = this._head.next;
let previous = this._head;
// Add the first item
if (!current)
{
listener.connect(previous);
}
else
{
// Go from highest to lowest priority
while (current)
{
if (listener.priority > current.priority)
{
listener.connect(previous);
break;
}
previous = current;
current = current.next;
}
// Not yet connected
if (!listener.previous)
{
listener.connect(previous);
}
}
this._startIfPossible();
return this;
}
/**
* Removes any handlers matching the function and context parameters.
* If no handlers are left after removing, then it cancels the animation frame.
*
* @param {Function} fn - The listener function to be removed
* @param {Function} [context] - The listener context to be removed
* @returns {PIXI.ticker.Ticker} This instance of a ticker
*/
remove(fn, context)
{
let listener = this._head.next;
while (listener)
{
// We found a match, lets remove it
// no break to delete all possible matches
// incase a listener was added 2+ times
if (listener.match(fn, context))
{
listener = listener.destroy();
}
else
{
listener = listener.next;
}
}
if (!this._head.next)
{
this._cancelIfNeeded();
}
return this;
}
/**
* Starts the ticker. If the ticker has listeners
* a new animation frame is requested at this point.
*/
start()
{
if (!this.started)
{
this.started = true;
this._requestIfNeeded();
}
}
/**
* Stops the ticker. If the ticker has requested
* an animation frame it is canceled at this point.
*/
stop()
{
if (this.started)
{
this.started = false;
this._cancelIfNeeded();
}
}
/**
* Destroy the ticker and don't use after this. Calling
* this method removes all references to internal events.
*/
destroy()
{
this.stop();
let listener = this._head.next;
while (listener)
{
listener = listener.destroy(true);
}
this._head.destroy();
this._head = null;
}
/**
* Triggers an update. An update entails setting the
* current {@link PIXI.ticker.Ticker#elapsedMS},
* the current {@link PIXI.ticker.Ticker#deltaTime},
* invoking all listeners with current deltaTime,
* and then finally setting {@link PIXI.ticker.Ticker#lastTime}
* with the value of currentTime that was provided.
* This method will be called automatically by animation
* frame callbacks if the ticker instance has been started
* and listeners are added.
*
* @param {number} [currentTime=performance.now()] - the current time of execution
*/
update(currentTime = performance.now())
{
let elapsedMS;
// If the difference in time is zero or negative, we ignore most of the work done here.
// If there is no valid difference, then should be no reason to let anyone know about it.
// A zero delta, is exactly that, nothing should update.
//
// The difference in time can be negative, and no this does not mean time traveling.
// This can be the result of a race condition between when an animation frame is requested
// on the current JavaScript engine event loop, and when the ticker's start method is invoked
// (which invokes the internal _requestIfNeeded method). If a frame is requested before
// _requestIfNeeded is invoked, then the callback for the animation frame the ticker requests,
// can receive a time argument that can be less than the lastTime value that was set within
// _requestIfNeeded. This difference is in microseconds, but this is enough to cause problems.
//
// This check covers this browser engine timing issue, as well as if consumers pass an invalid
// currentTime value. This may happen if consumers opt-out of the autoStart, and update themselves.
if (currentTime > this.lastTime)
{
// Save uncapped elapsedMS for measurement
elapsedMS = this.elapsedMS = currentTime - this.lastTime;
// cap the milliseconds elapsed used for deltaTime
if (elapsedMS > this._maxElapsedMS)
{
elapsedMS = this._maxElapsedMS;
}
this.deltaTime = elapsedMS * settings.TARGET_FPMS * this.speed;
// Cache a local reference, in-case ticker is destroyed
// during the emit, we can still check for head.next
const head = this._head;
// Invoke listeners added to internal emitter
let listener = head.next;
while (listener)
{
listener = listener.emit(this.deltaTime);
}
if (!head.next)
{
this._cancelIfNeeded();
}
}
else
{
this.deltaTime = this.elapsedMS = 0;
}
this.lastTime = currentTime;
}
/**
* The frames per second at which this ticker is running.
* The default is approximately 60 in most modern browsers.
* **Note:** This does not factor in the value of
* {@link PIXI.ticker.Ticker#speed}, which is specific
* to scaling {@link PIXI.ticker.Ticker#deltaTime}.
*
* @member {number}
* @readonly
*/
get FPS()
{
return 1000 / this.elapsedMS;
}
/**
* Manages the maximum amount of milliseconds allowed to
* elapse between invoking {@link PIXI.ticker.Ticker#update}.
* This value is used to cap {@link PIXI.ticker.Ticker#deltaTime},
* but does not effect the measured value of {@link PIXI.ticker.Ticker#FPS}.
* When setting this property it is clamped to a value between
* `0` and `PIXI.settings.TARGET_FPMS * 1000`.
*
* @member {number}
* @default 10
*/
get minFPS()
{
return 1000 / this._maxElapsedMS;
}
set minFPS(fps) // eslint-disable-line require-jsdoc
{
// Clamp: 0 to TARGET_FPMS
const minFPMS = Math.min(Math.max(0, fps) / 1000, settings.TARGET_FPMS);
this._maxElapsedMS = 1 / minFPMS;
}
}
