Planetary.js uses a plugin-based architecture, and all the built-in functionality is built using this architecture. This makes Planetary.js extremely flexible.
Plugins are loaded either globally by planetaryjs.loadPlugin or for a specific planet instance by planet.loadPlugin. If you call draw on a planet and it has no plugins loaded at all (from either source), Planetary.js will use the default plugin stack, which consists of the earth and pings plugins.
A plugin is simply a JavaScript function that takes a planet instance as a parameter and performs some operation on it. The best plugins do one tiny thing. If you want a plugin to do a lot of things at once, you should build a plugin that wraps other, smaller plugins; in fact, this is exactly how the earth plugin is built. See the Earth Plugin documentation for more details.
Most of the time, a plugin will implement its behavior by registering callbacks into a planet's lifecycle hooks. For example, the following simple plugin increments the planet's projection's rotation by one degree every tick (this would make for a very fast spinning globe, but demonstrates the idea nicely enough):
var autorotate = function(planet) {
planet.onDraw(function() {
var rotation = planet.projection.rotate();
rotation[0] += 1;
if (rotation[0] >= 180) rotation[0] -= 360;
planet.projection.rotate(rotation);
});
};
planet.loadPlugin(autorotate);Often, you'll want your plugin to be configurable with some user-defined values. In this case, you can create a higher-order function, which takes your configuration data and then returns the plugin function. You can then call this function to generate the plugin for use by loadPlugin.
var autorotate = function(degreesPerTick) {
return function(planet) {
planet.onDraw(function() {
var rotation = planet.projection.rotate();
rotation[0] += degreesPerTick;
if (rotation[0] >= 180) rotation[0] -= 360;
planet.projection.rotate(rotation);
});
};
};
planet.loadPlugin(autorotate(5));If you need to do some work before your plugin is ready to be used, you can add a hook to a planet's onInit hook to do the necessary setup.
var somePlugin = function(planet) {
planet.onInit(function() {
doSomeSetupWork();
});
};If you need to do some asynchronous setup--such as fetching data with an Ajax request--before your plugin is ready, you can accept an argument to your onInit function. This argument is a function that tells Planetary.js when you're done setting up; simply call this function after your asynchronous operations are complete and Planetary.js will continue to initialize the planet. If you accept the parameter but don't call it, the initialization process will stop (and your planet will not work).
var somePlugin = function(planet) {
planet.onInit(function(done) {
doSomeAsynchronousSetupWork(function() {
done();
});
});
};Many plugins will want to draw onto the globe's canvas; you can do so by registering a function to a planet's onDraw hook.
var somePlugin = function(planet) {
planet.onDraw(function() {
planet.withSavedContext(function(context) {
context.beginPath();
planet.path.context(context)({type: 'Sphere'});
context.fillStyle = 'black';
context.fill();
});
});
};The planet exposes properties and methods, such as context, path, and withSavedContext to assist with drawing to the canvas. The Planet API documentation goes into more detail on individual properties.
As explained in the planet.path documentation on the Planet API page, planet.path is a d3.geo.path object that can be used to draw geographical geometry onto the canvas. The path will take care of transforming the coordinates to be projected onto the orthographic view of the globe.
As a demonstration of this technique, the following is a plugin that will take the land data from a TopoJSON data source (stored on planet.plugins.topojson.world), convert it to a GeoJSON feature, and draw it on the planet. This code is similar to (but slightly simplified from) the Land plugin's implementation.
var drawLand = function(planet) {
planet.onDraw(function() {
planet.withSavedContext(function(context) {
var world = planet.plugins.topojson.world;
var land = topojson.feature(world, world.objects.land);
context.beginPath();
planet.path.context(context)(land);
context.fillStyle = 'white';
context.fill();
});
});
};Obviously, you can use private internal variables to keep track of any data your plugin needs in order to operate. However, if you want to expose a public API to users of your plugin, you should avoid attaching them directly to the planet and instead attach them to the planet's plugins namespace. You should use a name specific to your plugin, and this name should be well documented in your plugin's documentation.
var autorotate = function(degreesPerTick) {
return function(planet) {
var paused = false;
// Attach our public API to `planet.plugins`
// on the `autorotate` namespace.
planet.plugins.autorotate = {
pause: function() { paused = true; },
resume: function() { paused = false; }
};
planet.onDraw(function() {
if (paused) return;
var rotation = planet.projection.rotate();
rotation[0] += degreesPerTick;
if (rotation[0] >= 180) rotation[0] -= 360;
planet.projection.rotate(rotation);
});
};
};
planet.loadPlugin(autorotate(5));
planet.draw(canvas);
setTimeout(function() {
planet.plugins.autorotate.pause();
}, 5000);There are a few things you can do to make your plugin all it can be:
loadPlugin directly, even if your plugin doesn't take any configuration options. It makes for a more consistent API, and allows you to more easily add the ability to specify configuration options in the future.planet.plugins.pluginName, where pluginName is the name of your plugin.