Bergson is the scheduling system for Flocking and Aconite. It provides a variety of clocks driven by different sources (such as requestAnimationFrame, the Web Audio API, and setInterval), and a priority queue-based scheduler that allows you to queue up one-time and repeating function calls.
Bergson provides a very low-level API for scheduling, and is intended for library developers to build their own rhythmic and pattern-based abstractions on top of.
var scheduler = berg.scheduler({
components: {
clock: {
type: "berg.clock.requestAnimationFrame",
options: {
freq: 60
}
}
}
});
scheduler.start();
scheduler.schedule({
type: "once",
time: 30 // 30 seconds from now
callback: function (now) {
// Do something in the future.
}
});
scheduler.schedule({
type: "repeat",
time: 5, // Start repeating five seconds from now.
freq: 2, // Repeat every two seconds.
end: 20, // Stop repeating 20 seconds from now.
callback: function (now) {
// Do something repeatedly.
}
});
scheduler.clock.events.onTick.addListener(function (time, rate) {
// Do something every time the clock ticks.
});
A score event specification is a JSON-type (i.e. plain old, non-prototypal) object that describes the event to be scheduled. It can contain the following properties.
| Property | Value | Description |
|---|---|---|
| type | "once" or "repeat" |
The type of event to schedule (either one-time or repeating). |
| time | Number | The future time in seconds when the scheduled event should occur. |
| interval | Number | (Only for repeating events) The time interval, in seconds, between repetitions. This option takes precendence over freq if both are provided. |
| freq | Number | (Only for repeating events) The frequency at which the event should repeat. This option will be overridden by interval if both are provided. |
| end | Number | (Only for repeating events) The future time in seconds when the scheduled event should stop repeating. |
| callback | Function | The function to invoke. |
For more information on interacting with models, see the Infusion documentation about the Change Applier.
| Property | Description | Types |
|---|---|---|
| timeScale | The scheduler's time scale factor. Defaults to 1.0. | Number |
| Property | Description | Types |
|---|---|---|
| queue | The priority queue used to sort and queue score events. | berg.priorityQueue |
| Method | Description | Argument Types | Returns |
|---|---|---|---|
| start | Starts the scheduler and its clock. | none | undefined |
| stop | Stops the scheduler and its clock. | none | undefined |
| schedule | Schedules an event | A _score event specification_ object | The scheduled score event specification. |
| clear | Removes a scheduled event from the scheduler queue. | The _score event specification_ to clear. | undefined |
| clearAll | Removes all scheduled events from the scheduler queue. | none | undefined |
| setTimeScale | Sets the time scale factor for the scheduler. This will cause all time values for current and future scheduled events to be scaled by the specified value. | Number |
undefined |
| Property | Description | Types |
|---|---|---|
| time | The current clock time, in seconds. | Number |
| freq | The clock's frequency, in cyles per second. | Number |
| tickDuration | The duration between ticks, in seconds. | Number |
| Method | Description | Argument Types | Returns |
|---|---|---|---|
| start | Starts the clock. | none | undefined |
| stop | Stops clock. | none | undefined |
| tick | Advances the clock's time. (This will be invoked automatically for most clocks.) | None | undefined |
| Event Name | Description | Argument Types |
|---|---|---|
| onTick | Fires each time the clock ticks. | Number time: the current clock time in seconds |
| Clock | Description | Default rate |
|---|---|---|
berg.clock.requestAnimationFrame |
A clock that is driven at (or as near as possible to) the display's refresh rate by the browser's built-in requestAnimationFrame function. Note that this clock will be throttled down to
1 Hz automatically by the browser if its tab is not active. |
60 Hz. You must override this value if your display is running a different refresh rate. |
berg.clock.audioContext |
Uses the Web Audio API's AudioContext as a source of time. This clock
needs to be driven by your own ScriptProcessorNode code (i.e. by calling its tick() method within your onaudioprocess handler). This clock will not start ticking until its start() method is invoked by a user action (such as a button click). |
Dynamically determined based on the AudioContext's sampleRate and this clock's blockSize option. |
berg.clock.autoAudioContext |
An AudioContext-based clock that will automatically create a ScriptProcessorNode instance and wire it up correctly for you. Use this if you're not using the Web Audio API directly, but want a rock-solid clock for scheduling events in your application. This clock will not start ticking until its start() method is invoked by a user action (such as a button click). |
Dynamically determined based on the AudioContext's sampleRate and this clock's blockSize option. |
berg.clock.setInterval |
A clock that is driven by the browser's built-in (and notoriously jittery) setInterval function. Use this if you don't need significant reliability, and want maximal cross-environment compatibility (e.g. with Node.js). Note that this clock will be throttled down automatically
by the browser if its tab is not active. |
10 Hz |
berg.clock.workerSetInterval |
Like berg.clock.setInterval, except that it employs a Web Worker in order to avoid
the standard throttling done by browsers when the page is in the background. |
10 Hz |
berg.clock.offline |
A base grade for creating your own types of clocks. An offline clock tracks time relatively (i.e. without reference to a "real" source of time such as the system clock). This clock should be driven manually by invoking its tick() method. | 1 Hz |
berg.clock.realtime |
A base grade for creating your own types of clocks.
A realtime clock tracks time based on the actual system time using,
by default, performance.now().
This clock should be driven manually by invoking its tick() method. |
1 Hz |
Bergson uses Node.js, npm, Grunt, and Testem for its build and test tooling. Here's how to get set up:
1. Install the [Node.js](https://nodejs.org/en/) LTS release
3. Install Grunt: <code>npm install -g grunt-cli</code>
4. Install Testem: <code>npm install -g testem</code>
To download all of Bergson's dependencies, build them, and then build Bergson itself, run the following commands:
npm install
grunt
Bergson's test suite can be run on both Node.js and all of the browsers installed on your computer using Testem:
npm test
If you'd like to run only the Node.js tests, run:
npm run node-test
Or if you only want to run the browser tests:
npm run browser-test
Alternatively, if you'd like to only run the tests in one browser, you can open the test suite tests/unit/all-tests.html file by hand in your browser.
Bergson is supported by the Flocking community and uses its forums:
The Flocking mailing list is the place to ask questions, share code, and request new features.
Flocking has an IRC channel, which can also be used to ask questions about Bergson. Join #flocking on irc.freenode.net.
Bergson is written and maintained by Colin Clark. It is dually licensed under the MIT and GPL 2.0 licenses.
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