scratch-vm/src/util/timer.js

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/**
* @fileoverview
* A utility for accurately measuring time.
* To use:
* ---
* var timer = new Timer();
* timer.start();
* ... pass some time ...
* var timeDifference = timer.timeElapsed();
* ---
* Or, you can use the `time` and `relativeTime`
* to do some measurement yourself.
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*/
/**
* @constructor
*/
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const Timer = function () {};
/**
* Used to store the start time of a timer action.
* Updated when calling `timer.start`.
*/
Timer.prototype.startTime = 0;
/**
* Disable use of self.performance for now as it results in lower performance
* However, instancing it like below (caching the self.performance to a local variable) negates most of the issues.
* @type {boolean}
*/
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const USE_PERFORMANCE = false;
/**
* Legacy object to allow for us to call now to get the old style date time (for backwards compatibility)
* @deprecated This is only called via the nowObj.now() if no other means is possible...
*/
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const legacyDateCode = {
now: function () {
return new Date().getTime();
}
};
/**
* Use this object to route all time functions through single access points.
*/
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const nowObj = (USE_PERFORMANCE && typeof self !== 'undefined' && self.performance && 'now' in self.performance) ?
self.performance : Date.now ? Date : legacyDateCode;
/**
* Return the currently known absolute time, in ms precision.
* @returns {number} ms elapsed since 1 January 1970 00:00:00 UTC.
*/
Timer.prototype.time = function () {
return nowObj.now();
};
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/**
* Returns a time accurate relative to other times produced by this function.
* If possible, will use sub-millisecond precision.
* If not, will use millisecond precision.
* Not guaranteed to produce the same absolute values per-system.
* @returns {number} ms-scale accurate time relative to other relative times.
*/
Timer.prototype.relativeTime = function () {
return nowObj.now();
};
/**
* Start a timer for measuring elapsed time,
* at the most accurate precision possible.
*/
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Timer.prototype.start = function () {
this.startTime = nowObj.now();
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};
Timer.prototype.timeElapsed = function () {
return nowObj.now() - this.startTime;
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};
module.exports = Timer;