ftcolumnflow

FTColumnflow

FTColumnflow is a polyfill that fixes the inadequacies of CSS column layouts. It is developed by FT Labs, part of the Financial Times. It is extensively used in the FT Web App, where it allows us to publish articles with complex newspaper/magazine style layouts, including features such as:

• Configurable column widths, gutters and margins
• Fixed-position elements
• Elements spanning columns
• Keep-with-next to avoid headings at the bottom of a column
• No-wrap class to avoid splitting elements across columns
• Grouping of columns into pages
• Horizontal or vertical alignment of pages
• Standardised line height to align text baseline to a grid
• Rapid reflow as required by events such as device orientation or font-size change

It is designed with the same column dimension specification API as the CSS3 multi-column specification (specify columnWidth, columnCount and/or columnGap), but gives far greater flexibility over element positioning within those columns.

Usage

Include FTColumnflow.js in your JavaScript bundle or add it to your HTML page like this:

<script type='text/javascript' src='/src/FTColumnflow.js'></script>

The script must be loaded prior to instantiating FTColumnflow on any element of the page. FTColumnflow adds pages and columns to the DOM inside a specified target element, which must be a child of the viewport element. The resulting pages are the same dimensions as the viewport, which allows for a scrolling window of multiple targets and pages to sit inside it.

FTColumnflow accepts two types of content—fixed and flowed—which can be specified either as text strings or as DOM nodes from which to copy elements. Fixed elements can be positioned using CSS classes to specify page number, vertical/horizontal anchoring, column span and span direction. Flowed elements will be flowed over columns and pages (created automatically) and can optionally include CSS classes to control wrapping behaviour.

To activate FTColumnflow on an article, create a target element inside a viewport:

<section id="viewport">
	...
	<article id="article-1"></article>
	...
</section>

Create a new instance of FTColumnflow, passing either ID names or DOM element references for target and viewport, along with an object of configuration parameters (all of which are optional):

var cf = new FTColumnflow('article-1', 'viewport', {
	columnCount: 3,
	standardiseLineHeight: true,
	pagePadding: 30,
});

or:

var articleEl  = document.getElementById('article-1');
var viewportEl = document.getElementById('viewport');

var cf = new FTColumnflow(articleEl, viewportEl, {
	columnCount: 3,
	standardiseLineHeight: true,
	pagePadding: 30,
});

To render flowed content, pass either text strings or DOM nodes into the FTColumnflow.flow() method. For example, if you have the following content, separated into flowed and fixed groups:

<div id="flowedContent">
	<p>One morning, when Gregor Samsa woke from troubled dreams, he found himself transformed in his bed into a horrible vermin. He lay on his armour-like back, and if he lifted his head a little he could see his brown belly, slightly domed and divided by arches into stiff sections.</p>
	<p>The bedding was hardly able to cover it and seemed ready to slide off any moment. His many legs, pitifully thin compared with the size of the rest of him, waved about helplessly as he looked. "What's happened to me? " he thought. It wasn't a dream.</p>
	...
</div>

<div id="fixedContent">
	<div class="col-span-2">
		<h1>The Metamorphosis</h1>
		<h2>Franz Kafka, 1915</h2>
	</div>
	<figure class="anchor-bottom-col-2">
		<img src="http://upload.wikimedia.org/wikipedia/commons/thumb/7/71/Metamorphosis.jpg/147px-Metamorphosis.jpg" style="width: 147px; height: 239px;" />
	</figure>
</div>

You could apply FTColumnflow to this content with code such as:

var flowedContent = document.getElementById('flowedContent'),
	fixedContent  = document.getElementById('fixedContent');

cf.flow(flowedContent, fixedContent);

Alternatively, you can pass your content into the flow method directly:

cf.flow(
	'<p>One morning, when Gregor Samsa woke from troubled dreams...',
	'<div class="col-span-2"><h1>The Metamorphosis</h1><h2>Franz Kafka, 1915</h2></div>...'
);

Examples

Here are some examples of FTColumnflow in use - feel free to copy the code and use as the basis for your own projects.

• Basic usage example
• FTColumnflow elements highlighted, which shows the derived baseline grid, the pages and columns, and also exposes the mechanism by which FTColumnflow overflows columns with content, then hides the overflow.
• Vertically-orientated pages
• noWrap class and noWrapOnTags config setting
• Another layout
• Native CSS3 columns, demonstrating the capability of CSS columns without using FTColumnflow.

How does it work?

With FTColumnflow, FTLabs have addressed some of the limitations of the CSS3 multi-column specification. We needed an approach which would give accurate and flexible newspaper-style column layouts, to which we could add fixed-position elements spanning over any number of columns.

Flowing text over columns using JavaScript is not so easy: although it's trivial for a human to spot the last word before a column boundary, not so for a computer. Our first iteration looped through each word in the flowed text to determine whether or not it was within the bounds of the current column. When the first out-of-bounds word was found, the paragraph was split, and the second part moved over to a new column. However, this was found to be very slow and DOM-heavy, especially with long paragraphs.

We then realised that we didn't need to split the paragraphs to prevent out-of-bounds words being seen - we could do the same using overflow: hidden. So the new approach is to determine where in a paragraph the column's bottom boundary will fall, and to copy that paragraph to a new column, with a negative top margin equal to that of the overflow. This example shows a FTColumnflow layout with its internals exposed - it can be seen that paragraphs overflow the purple column boundaries, but are repeated in the following column, shifted up so that the next line of text is visible.

One important consideration for this approach is that, using overflow: hidden, it's possible for a column's boundary to chop off part of a line of text - see this broken example. Here, the line-height of the page elements is not correctly configured in relation to the height of the columns - there is no consistent baseline grid. For a succesful layout with FTColumnflow, it is important that the column height is a whole multiple of the grid height, and that all elements are placed on the grid.

Setting the standardiseLineHeight configuration option to true (it defaults to false) will automatically determine the baseline grid from your page's CSS. It will ensure that column heights are multiples of the grid height, and will pad all fixed and flowed elements to ensure they conform to the grid. See the same example with standardiseLineHeight: true.

Configuration

Configuration options can be specified at create-time by passing a JSON object as the third argument to the FTColumnflow constructor. All parameters are optional; any which are specified will override default values.

Column dimension configuration is designed to be as close as possible to the CSS3 multi-column specification, using the same logic to determine columnWidth, columnCount and columnGap.

• pageClass: 'mypageclass',

  Class name to add to each page created by FTColumnflow. Class names are normalised (invalid characters are replaced with a -). (String, default 'cf-page')

• columnClass: 'mycolumnclass',

  Class name to add to each column created by FTColumnflow. Class names are normalised (invalid characters are replaced with a -). (String, default 'cf-column')

• viewportWidth: 800,

  Viewport width in pixels if known, otherwise it will be measured. Note this is not the browser viewport, but refers to a DOM element passed to the FTColumnflow constructor. See Public interface for details. (Integer, default null)

• viewportHeight: 600,

  Viewport height in pixels if known, otherwise it will be measured. Note this is not the browser viewport, but refers to a DOM element passed to the FTColumnflow constructor. See Public interface for details. (Integer, default null)

• layoutDimensionsCache: {...},

  Pass in cached values from a previous invocation of FTColumnflow with exactly the same configuration parameters and viewport dimensions. These can be obtained from a previous flow using cf.layoutDimensions; (Object, default null)

• pageArrangement: 'horizontal',

  Pages are absolutely positioned with respect to the target parent container. This parameter determines their arrangement. ('horizontal'|'vertical', default 'horizontal')

• pagePadding: 10,

  Padding in pixels to add to each page (resulting page + padding will equal the viewport dimensions). For horizontal arrangement, padding is added to left/right only, and for vertical to the top/bottom only. (Integer, default 0)

• columnFragmentMinHeight: 20,

  Minimum height of each column 'fragment', in pixels. If fixed-position elements result in shortened, fragmented columns, no blocks of text will be shorter than this value. (Integer, default 0)

• columnWidth: 200,

  Optimal column width in pixels, or 'auto'. Integer must be greater than 0. The actual columns may be wider (to fill the available space) or narrower if the specified columnWidth is greater than the available width. A value of auto will result in a column width determined by using the other properties (columnCount and columnGap). (Integer|'auto', default 'auto')

• columnCount: 3,

  Optimal number of columns per page, or 'auto'. Integer must be greater than 0. If both columnWidth and columnCount are defined, columnCount is the maximum number of columns per page. A value of auto will result in a column count determined by using the other properties (columnWidth and columnGap). (Integer|'auto', default 'auto')

• columnGap: 20,

  Column gap in pixels, or 'normal'. Integer must be greater than 0. The default value, 'normal', is set to 1em. (Integer|'auto', default 'normal')

• standardiseLineHeight: true,

  If false, FTColumnflow assumes all column content is corrected/padded to conform to a baseline grid (for example, paragraph margins should be a multiple of their line-height value), and determines the grid height from the lineheight of a paragraph. If true, FTColumnflow uses the mode of the first few line-heights found, and adds padding to all other element to conform to the grid. (Boolean, default false)

• lineHeight: 20

  Specify the line-height of the flowed content. If not set, it will be determined by analysing the content. (Integer, default null)

• minFixedPadding: 0.5,

  Minimum space between fixed elements and columns, expressed as a multiple of the grid height. (Float, default 1)

• noWrapOnTags: ['figure', 'h3', ...],

  Assume a 'nowrap' class for every element which matches the list of tags. (Array, default [])

• showGrid: true */,

  Show the baseline grid - very useful for debugging line-height issues. (Boolean, default false)

• debug: true */,

  Print internal calls to _log() to the console (Useful for development, not used in this release). (Boolean, default false)

Public interface

Constructor

• var cf = new FTColumnflow(target, viewport, {...});

  Instantiate an FTColumnflow instance, which will operate on target within viewport.

  • target

    DOM element, or element ID attribute, into which FTColumnflow should write pages and columns. This should be an empty container; all contents will be overwritten.

  • viewport

    DOM element, or element ID attribute, for the viewport from which to determine page and column dimensions.

  • config

    Object of key/value configuration pairs (see Configuration above).

  When FTColumnflow is instantiated on an element, the return value from the constructor is an object that offers a number of public properties, methods and events.

Methods

• flow(flowed, fixed);

  Flow flowed content over columns and pages, and position fixed content according to style rules on the elements.

  • flowed

    DOM element containing content to flow, or an HTML string of elements. Flowed elements may optionally specify CSS classes to control wrapping behaviour:

    • nowrap

      This element must not span a column break (eg. an image, header, etc.).

    • keepwithnext

      Avoid a column or page break after this element; prefer a break before if necessary

  • fixed

    DOM element containing content to position absolutely, or an HTML string of elements. Fixed elements are anchored in the order they appear in the DOM, so the second item to be anchored top-left will appear underneath the first (with a margin equal to one grid height). Elements should be given CSS classes to specify their position on the page:

    • anchor-<vertical-pos>-<horizontal-pos> OR anchor-<vertical-pos>-col-<n>

      Page position to which fixed element should be anchored. (Default anchor-top-left).

      • vertical-pos : [top, middle, bottom]
      • horizontal-pos : [left, right]
      • n : integer

    • col-span-<n|all>[-<left>|-<right>]

      Fixed element should span n columns (or all columns), optionally specifying a direction in which to span. (Default: col-span-1, default span direction: right).

    • attach-page-<n>

      Fixed element should appear on page n. (Default: attach-page-1).

• reflow({});

  Re-flow the same content using different configuration parameters. This is useful when a hand-held device is rotated (orientationchange event), or font-sized is changed on the page, for example.

  • config

    Object of key/value configuration pairs (see Configuration above).

• destroy();

  Destroy the FTColumnflow DOM nodes, and free up memory.

Properties

All public properties are read-only.

• pageClass

  The normalised class name added to pages (see pageClass in Configuration above).

• columnClass

  The normalised class name added to columns (see columnClass in Configuration above).

• pageCount

  The number of pages created by the last run of cf.flow()

• layoutDimensions

  The dimensions configuration object produced by the last run of cf.flow(). This can be cached externally, and fed back into FTColumnflow using the layoutDimensionsCache config parameter (see Configuration above) to reduce calculations and DOM reads on subsequent flows.

  Example output:

{
	"pageInnerWidth":  740,
	"pageInnerHeight": 600,
	"colDefaultTop":   0,
	"colDefaultLeft":  30,
	"columnCount":     3,
	"columnWidth":     236,
	"columnGap":       16
}

Compatibility

FTColumnflow supports the following browsers:

• Google Chrome (18+)
• Apple Safari (5+)
• Firefox (10+)
• Mobile Safari (iOS 5+)
• Android browser (ICS+)
• Blackberry browser (PlaybookOS 2.0.1+)
• Microsoft Internet Explorer (10+)

Testing

FTColumnflow is a fully Test-Driven codebase. Modifcations to the code should have an accompanying test case added to verify the new feature, or confirm the regression or bug is fixed.

NOTE: as of 28th June 2012, FTColumnflow no longer uses JsTestDriver as a test framework - we found it was too limited in scope, and that Buster.js fulfilled all the features and more.

FTColumnflow uses Buster.js as a TDD framework. This requires Node and NPM - installation instructions are at http://busterjs.org/docs/getting-started/. Buster.js creates an HTTP server to which any number of real browsers can be attached; the tests will be performed on each browser.

Usage

• Change to FTColumnflow directory:

  $ cd [FTColumnflow root directory]
  

• Start test suite server:

  $ buster server
  buster-server running on http://localhost:1111
  

  Buster.js has now started a server - in this case, on port 1111 (use $ buster server -p 1234 to specify the port). Visit http://localhost:1111 in any number of browsers, and capture them to run tests in those browser.

• Run tests in a new shell:

  $ buster test
  

  There are a number of options for test output - see the reporters documentation and the Reporters examples at the bottom of the overview page.

Credits and collaboration

The lead developer of FTColumnflow is George Crawford at FT Labs. All open source code released by FT Labs is licenced under the MIT licence. We welcome comments, feedback and suggestions. Please feel free to raise an issue or pull request. Enjoy.