Apollolux: created from http://web.archive.org/web/20110802085151/http://www.spheredev.org/wiki/GetTime

2013-06-01T22:46:19Z

created from http://web.archive.org/web/20110802085151/http://www.spheredev.org/wiki/GetTime

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Obtains the number of milliseconds elapsed since an arbitrary time.

==Usage==

{{Usage|returns=integer|func=GetTime}}

==Examples==

<syntaxhighlight>
var time = GetTime();
</syntaxhighlight>

The above gets the number of milliseconds passed since some predetermined time, and places it in the <var>time</var> variable.

<syntaxhighlight>
var start_time = GetTime();
// Code that needs to be timed
// ...
var duration = GetTime() - start_time;
</syntaxhighlight>

The above example will find out how long a particular piece of code runs for.

<syntaxhighlight>
function Delay(ms)
{
var start = GetTime();
while (GetTime() - start < ms);
}
</syntaxhighlight>

The above function is a simple mechanism to pause script execution for a given number of milliseconds, called using, for example, <code>Delay(1500);</code>, which pauses script execution for one and a half seconds. No updating or redrawing will take place while the delay is occurring.

<syntaxhighlight>
var done = false;
var fps = GetFrameRate();
var updates_performed = 0;
var start_time = GetTime();
while (!done)
{
while (updates_performed < (GetTime() - start_time) * 0.001 * fps)
{
// Update game here
// ...
updates_performed++;
}
// Draw the game screen here
// ...
FlipScreen();
}
</syntaxhighlight>

The above example is one way to regulate the speed of a Sphere game inside a JavaScript loop. The game code will have to be separated into updates (player input processing, moving entities, checking collisions, etc.) and drawing (drawing sprites, the map, score, etc.).

<syntaxhighlight>
var FPS = 60; // The desired FPS
var delayTime = 1000/FPS; // The time between frames
var lastTime = GetTime(); // The time of the last frame
while(loopCondition) // While we should continue looping
{
if(GetTime() > lastTime + delayTime) // If enough time has elapsed
{
lastTime = GetTime(); // Record the time of this frame
doStuff(); // Do your stuff
}
drawStuff(); // Draw your stuff
}
</syntaxhighlight>

This example is an alternative to the one above. Obviously, doStuff() and drawStuff() will correspond with functions that actually process the game logic and draw the game state respectively.

==Notes==
* The starting time can be assumed to be constant throughout the running of a game. Thus GetTime() is very useful as a tool to pace JavaScript loops, which would normally run at different speeds on different systems.
* Core JavaScript provides a similar mechanism via the [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date Date] object's [https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getTime Date.getTime]() method. This counter, if used with a Date object that reflects the current time, displays the number of milliseconds since midnight 01 January, 1970 UTC. Refer to the links for more information.
* Because GetTime() is a signed integer, it will wraparound from time to time.

==See also==
* [[API:FlipScreen|FlipScreen]]()
* [[API:GetFrameRate|GetFrameRate]]()
* Core JavaScript [https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date Date] object
* Core JavaScript [https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Date/getTime Date.getTime]()

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Legacy:GetTime - Revision history

Apollolux: created from http://web.archive.org/web/20110802085151/http://www.spheredev.org/wiki/GetTime