Popcorn.js Base Plugin is a wrapper for creating Popcorn plugins that conform to the Best Practices guide. The goals of the Best Practices are to provide the best user experience, to empower authors who may or may not have advanced programming skills and to make plugins general and reusable.
Base Plugin is opinionated, assuming and enforcing standards for certain argument names and behaviors.
- Event callbacks added to
_setup,start,end,frameand_teardown - Discover target element
- Clean up plugin definition, filling in a "nop" for missing events
- Create container element, maintaining time order in DOM
- Easily animate parameters in
framemethod, with keyframes and multiple tweening functions - Provide access to normalized data for certain arguments
- Automatically clean up container element on
_teardown - Enable any CSS parameter names to be mapped directly to style of container element
- Utility: parse out array/object arguments from JSON or delimited strings
- Utility: cross-browser addClass/removeClass shim (no external libraries required)
- Display/hide container elements using CSS classes rather than element style
- Convert animations to CSS when available and appropriate
- Handle localization
- Add
loadevent method for retrieving remote resources when needed
Popcorn.basePlugin('myplugin', function(options, base) {
/*
* Closure variables and functions go here
* `base` is BasePlugin object for access to utilities
* `options` remains unchanged
*/
if (!base.target) {
/*
* This particular plugin requires a target element.
* If not target is specified (e.g. a new event in Popcorn
* Maker), return without doing anything.
*
* Base Plugin will handle creating empty `start` and `end`
* native methods so you don't have to worry about it.
*/
return;
}
return {
_setup: function( event, options ) {
/* optional. setup can be performed in parent function */
},
start: function( event, options ) {
},
frame: function( event, options ) {
},
end: function( event, options ) {
},
_teardown: function( options ) {
}
};
});
Authors using a plugin may specify callback functions to be called at
various points in the lifecycle of a track event: onSetup, onStart,
onFrame, onEnd and onTeardown. The onEnd and onTeardown
callbacks are run before the plugin's respective native method, if any;
others are run after the native method. Callbacks are run even if no
native method exists.
Inside a callback function, this represents the PopcornBaseEvent
object. The first and only argument is the event's options object,
except for onFrame, which takes the current time in seconds as the
second argument.
Base Plugin will wrap callbacks in try...catch so a crashing callback
will not break the plugin, but a stack trace, where available, will be
logged to the error console.
Callbacks are specified by assigning a function to an event's options
object:
popcorn.myplugin({
start: 0,
end: 1,
onStart: function(options) {
console.log('Event started at ' + options.start + ' seconds');
},
onFrame: function(options, time) {
}
});
Callbacks can alternatively be specified with a string representing the
name of a global function. This may be useful if Popcorn event data is
passing through a channel that does not allow functions, such as a JSON
blob or through a window.postMessage.
window.handleEventStart = function(options) {
console.log('Event started at ' + options.start + ' seconds');
};
popcorn.myplugin({
start: 0,
end: 1,
onStart: 'handleEventStart'
});
The second arugment passed to the definition function is an instance of
BasePluginEvent, which provides access to useful data and utility
methods.
The original options object passed to event creation. This object
remains unchanged.
An HTMLElement representing the target element in which to place
the event's container. If the original options.target is a string,
Base Plugin will search for an event with that id attribute. If no
element is found, .target will be undefined.
Element created by makeContainer, if any.
The name with which the plugin is registered on the global Popcorn object.
A reference to the function representing the respective callback. If the original was a string, this is the resolved function. If no function was found or the original is of the wrong type, this is undefined.
Creates a container element, which is set as the container property of
the BasePluginEvent and returned by this method. The container element
is inserted as a child of the target element, if it exists.
Containers are inserted in ascending time order, first by start, then
by end. Regardless of the order in which events are created, consistent
order in the DOM is guaranteed (except for events with the same start
and end time).
The first argument tag specifies the tag name with which to create the
element. If this is missing or evaluates to false, the default is 'div'.
The second argument insert, if false (but not undefined), will
prevent the insertion of the container element into the DOM.
Popcorn.basePlugin('myplugin', function(options, base) {
if (!base.target) {
return;
}
base.makeContainer();
base.container.appendChild(
document.createTextNode(options.text || '')
);
/* etc.... */
});
Specifies a given options parameter as one that can be animated.
Authors can specify start end, and keyframe values by setting the parameter as an object where each property is a keyframe with the property key representing the time.
Values must be a number or string, and any numbers found within will be interpolated. Mixed strings are not allowed, so any keyframes that don't match the first one listed will be ignored. Hexidecimal colors will be translated to rgb or rgba values for interpolation. If the parameter is not an object, it is set but not animated.
Note: parameters cannot be animated unless Popcorn is given the frameAnimation option.
Plugins are provided animated values as follows:
var popcorn = Popcorn('#video', {
frameAnimation: true //don't forget this
});
popcorn.myplugin({
start: 0,
end: 1,
top: {
from: '10px',
to: '50px'
}
})
Multiple keyframes can be provided by specifying times as keys on the object. 'from' and 'to' can be used as aliases for 0 and 1, respectively. Keyframe times range from 0 to 1, and the times are scaled to the full length of the event. Anything outside that range is ignored.
var popcorn = Popcorn('#video', {
frameAnimation: true //don't forget this
});
popcorn.style({
start: 0,
end: 10,
bottom: {
0: '0px',
0.2: '100px', // at 2 seconds (0.2 * 10 = 2)
1: '0px' // at 10 seconds (1 * 10 = 10)
}
})
By default, values are interpolated linearly, but it is possible to specify a timing function, similarly to the kind applied to CSS animation. A timing function is set for a block of keyframes by setting the timing property to a string, which represents the name of the timing function (see documentation below for a list) and optional parameters.
popcorn.style({
start: 0,
end: 10,
bottom: {
0: '0px',
0.2: '100px', // at 2 seconds (0.2 * 10 = 2)
1: '0px' // at 10 seconds (1 * 10 = 10),
timing: 'cubic-bezier(0.1, 0.7, 1.0, 0.1)'
}
})
Each key frame can be given its own timing function:
popcorn.style({
start: 0,
end: 10,
timing: 'linear',
bottom: { //fly up to the top and then bounce to the bottom
0: '0px', //will use 'linear, the default'
0.2: {
val: '100px',
timing: 'bounce(100)' //first parameter is how much gravity
},
1: '0px' // at 10 seconds (1 * 10 = 10)
}
})
To animate a parameter, call base.animate in the plugin definition with the first parameter
as the name of the option. All options will be provided in base.options with the correct values
at any given time.
Popcorn.basePlugin('myplugin', function(options, base) {
base.animate('top');
/* etc.... */
return {
/* etc.... */
frame: function(event, options, time) {
this.container.style.top = this.options.top;
}
}
});
Optionally, animate can take a second argument specifying options. Currently, the only option
available is callback, which specifies a function to be called with the current value whenever
it is animated.
Popcorn.basePlugin('myplugin', function(options, base) {
base.makeContainer();
base.animate('top', {
callback: function(val) {
this.container.style.top = val;
}
});
/* etc.... */
});
As an alternate syntax, it is possible to simply pass the callback function in place of an object.
Popcorn.basePlugin('myplugin', function(options, base) {
base.makeContainer();
base.animate('top', function(val) {
this.container.style.top = val;
});
/* etc.... */
});
If a DOM Element is supplied in place of the callback function, animate will instead apply the animated property to the style of that element.
Popcorn.basePlugin('myplugin', function(options, base) {
base.makeContainer();
base.animate('top', this.container); //animate the 'top' CSS property
/* etc.... */
});
If no property name is supplied, and the only parameter is a DOM Element, all styles specified in the event's options will be animated. When base.animate() is called with no parameter, all styles are animated on the container element, if it exists.
Popcorn.basePlugin('myplugin', function(options, base) {
base.makeContainer();
base.animate(this.container); //Animate all styles!
});
When setting style properties that require experimental vendor prefixes, it is possible to substitute -*- for the vendor prefix. Popcorn Base will first try to set the non-prefixed style and then try each of the major browser vendor prefixes. If the same property is set with a full browser prefix, it will not be over-written.
popcorn.style({
start: 0,
end: 2,
'-*-transform': { //spin clockwise
from: 'rotate(0deg)',
to: 'rotate(360deg)'
},
'-moz-transform': { //...unless it's firefox; rotate counter-clockwise
from: 'rotate(360deg)',
to: 'rotate(0deg)'
}
})
A static utility method for retrieving an array from an input of
undetermined type. First argument data may be an array, a JSON string,
a single value or object, or a string to be split. Returned value is
guaranteed to be an array. If data is a single value or object,
toArray will return an array with that value as the only element.
If data is a string and the second argument delimiters is specified,
it will be used to split the string into an array. This should be a
string or RegExp, as per Javascript's String.split.
A static utility method for retriving an object. If data argument is
a JSON string, it will be parsed and the result will be returned.
Otherwise, data will be returned unchanged.
A utility for adding one or more classes to a DOM element. This method wraps (or polyfills) classList.add.
Unlike classList.add, classes can be an array or a string delimited
by spaces, returns, newlines or commas. Duplicates will be removed.
Though most desktop browsers that support HTML5 video also support
classList natively, it is still missing from Internet Explorer
and iOS before v5.0, so a polyfill is provided.
Similar to addClass, but removes any classes specified in the second
argument.
A range of timing functions are provided for use in keyframing. Some functions replicate the CSS Animation timing functions, but additional, more complex functions are provided as well.
All functions are accessible in the Popcorn.basePlugin.timing object. These may be useful within the plugin itself or for visualizing the path of the timing function on a canvas. Each function in the timing object is a "function factory" that will accept the configuration parameters and return the actual timing function.
var cubicBezier;
//list all the timing functions
for (i in Popcorn.basePlugin.timing) {
console.log('i'); //put these in a <select> element when building your editor
}
cubicBezier = Popcorn.basePlugin.timing['cubic-bezier'](0.1, 0.7, 1.0, 0.1);
cubicBezier(0); // 0
cubicBezier(1); // 1
cubicBezier(0.25); // 0.44075538703700035
The default timing function, linear progresses the animation from start to finish at constant speed.
A cubic Bézier curve which replicates the cubic-bezier timing in CSS Animation. This is extremely flexible but can be difficult to use by hand.
x1, y1, x2, y2 are numbers representing the coordinates of P1 and P2 of the curve. x1 and x2 must be between 0 and 1 (inclusive). Defaults are: 0.25, 0.1, 0.25, 1.0; the same as ease.
Timing proceeds in n equidistant steps, as in a staricase function. At each step, the animation jumps to the end state and stays in that position until the next step or keyframe.
Replicates CSS step-start.
n - the number of steps, must be greater than zero.
Timing proceeds in n equidistant steps, as in a staricase function. At each step, the animation stays at the initial state and jumps to the final position at the end of the step.
Replicates CSS step-end.
n - the number of steps, must be greater than zero.
Begins slowly, accelerates and stops abruptly. Identical to cubic-bezier(0.42, 0.0, 1.0, 1.0).
Replicates CSS ease-in.
Begins slowly, accelerates and slows down. Identical to cubic-bezier(0.42, 0.0, 0.58, 1.0).
Replicates CSS ease-in-out.
Starts quickly and slows down. Identical to cubic-bezier(0.0, 0.0, 0.58, 1.0).
Replicates CSS ease-out.
Similar to ease-in-out, but accelerates faster at the beinning and slows down more gradually. Identical to cubic-bezier(0.25, 0.1, 0.25, 1.0).
Replicates CSS ease.
Similar to standard CSS easing functions, but eases on a square (a.k.a. "quadratic") curve, like a parabola.
Like quad functions, but progresses on a cubic function (i.e. "t^3") rather than square function. Acceleration and deceleration are steeper than quad.
Like quad and cubic, but uses a quartic function (i.e. "t^4"). Steeper than cubic.
Ease on a quintic function (i.e. "t^5"). Steeper than quartic.
Like quad, cubic, quart and quint functions, but will operate on any arbitrary power for finer control.
power - the power to which to raise the time. Must be a number greater than or equal to zero. Default is 1 (same as linear).
ease-in-power(3)is the same as `ease-in-cubic'ease-in-power(1)is the same as `linear' (but not as efficient)ease-in-power(8)is very steep acceleration and decelerationease-in-power(2.5)steeper than quadratic, but not as steep as cubic
Ease along the first part of a sine curve. More subtle than quadratic.
Ease along an exponential curve 2^(10*(t-1)). Very gradual at the ends and quick in the middle.
Circular easing along an arc, as on the curve of a quarter-circle.
Animation accelerates towards and end bounces against it multiple times like a ball falling to the ground. Each successive bounce is diminished until it settles at the end point.
gravity - Rate of acceleration towards the end point. Since the animation scales to the duration of the Popcorn event, you will probably need to play around with this value until you find the setting that looks good. Must be a number greater than zero. A gravity value of 2.0 will make the first "drop" from 0 to 1 take the entire time of the animation.
bounce - A number from 0 to 1 that represents the "height" of each bounce. When set to 0, the animation will accelerate to the end and then stop. At 1, the animation will bounce without diminishing until the end of the event (and stop abruptly).
Popcorn Base Plugin is made available under the MIT License.
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