Slabtype algorithm now a jQuery plugin

Algorithms, Digital Humanities, Graphic Design, jQuery, Source Code, Typography


Slabtype, the text rendering algorithm I developed for Public Secrets, has been adapted by web developer Brian McAllister as a jQuery plugin. If you’re interested, you can read details about the inner workings of the original algorithm. Very gratifying to see past work live on in new forms!


The slabtype algorithm, Part 4: Final layout and source code

Algorithms, Flash, Graphic Design, Interactive Design, Source Code, Typography

This is the final installment of a four-part graphical dissection of the “slabtype” text layout algorithm I developed for Public Secrets. For an introduction to the algorithm, visit The slabtype algorithm, Part 1: Background. To review some calculations that set the stage, visit Part 2: Initial calculations. To get into the real meat of the algorithm, visit Part 3: Iterative line splitting.

In this post, we’ll wrap things up by doing our final layout of the text, followed by the source code for the algorithm. The iterative sequence we explored in the previous installment successfully turned our original text:

Original text

into seven separate lines:

All seven lines

We’re almost done. Our next task is to assemble these lines into a slab by scaling them all to an identical pixel width:

Scaled lines

And finally, to scale the entire slab to fit inside the original box, allowing for a minimum amount of padding on each side:

Scaled lines inside slab

And with that, the algorithm has run its course. In conjunction with the treemap algorithm, the slabtype algorithm allows us to dynamically lay out the entire contents of a screen like this

A screen full of slabtype

using only a collection of quotes as a starting point. Due to randomization in the input to the treemap algorithm, even identical collections of quotes are never laid out in exactly the same way. Within Public Secrets, you can briefly see the dynamism of the slabtype algorithm in action when a box containing a quote resizes as it moves from one location to another—the text inside shifts around to keep pace with the changing dimensions of its enclosing rectangle.

This algorithm was included in Public Secrets as a method called formatInscription, which is reproduced below (AS 2.0). I hope this has been a useful exercise—I’d love to get your feedback, questions, or suggestions for improvement.

    /* -- formatInscription : formats the text to fit the slab dimensions -- */
    public function formatInscription(rect:Rectangle, useMargin:Boolean):Void {
        // calculate height of the ’ideal’ line
        var idealLineAspectRatio:Number = PS.fontInfo.altGoth3D.aspectRatio * PS.fontInfo.altGoth3D.idealLineLength;
        var idealLineWidth:Number = rect.width;
        var idealLineHeight:Number = idealLineWidth / idealLineAspectRatio;
        var lineCount:Number = Math.floor(rect.height / idealLineHeight);
        var idealCharPerLine:Number = Math.min(60, Math.max(Math.round(this._inscription.length / lineCount), 1));
        // segment the text into lines
        var words:Array = this._inscription.split(“ ”);
        var lineBreaks:Array = new Array();
        var preText,postText,finalText:String;
        var preDiff,postDiff:Number;
        var wordIndex:Number = 0;
        var lineText:Array = new Array();
        var counter:Number = 0;
        // while we still have words left, build the next line
        while (wordIndex < words.length) {
            postText = “”;
            // build two strings (preText and postText) word by word, with one
            // string always one word behind the other, until
            // the length of one string is less than the ideal number of characters
            // per line, while the length of the other is greater than that ideal
            while (postText.length < idealCharPerLine) {
                preText = postText;
                postText += words[wordIndex]+“ ”;
                if (wordIndex >= words.length) {
            // calculate the character difference between the two strings and the
            // ideal number of characters per line
            preDiff = idealCharPerLine - preText.length;
            postDiff = postText.length - idealCharPerLine;
            // if the smaller string is closer to the length of the ideal than
            // the longer string, and doesn’t contain just a single space, then
            // use that one for the line
            if ((preDiff < postDiff) && (preText.length > 2)) {
                finalText = preText;
            // otherwise, use the longer string for the line
            } else {
                finalText = postText;
            lineText.push(finalText.substr(0, finalText.length-1));
        lineCount = lineText.length;
        // create inscription clip
        this.createEmptyMovieClip(“inscriptionClip”, 10);
        this._inscriptionClip = this[“inscriptionClip”];
        // build the text fields
        var curY:Number = 0;
        this._lines = new Array();
        for (var i:Number=0; i<lineCount; i++) {
            this._inscriptionClip.attachMovie(“altGoth3DText”, “line”+i, 10+i);
            this._lines[i].content.text = lineText[i];
            // scale this line so it exactly fits with width of the rect
            this._lines[i]._yscale = this._lines[i]._xscale = (rect.width / this._lines[i].content.textWidth) * 100;
            this._lines[i]._y = curY;
            curY += this._lines[i]._height * .59;
        this._inscriptionWidth = rect.width;
        this._inscriptionHeight = curY;
        this._inscriptionAR = this._inscriptionWidth / this._inscriptionHeight;
        if (useMargin) {
            var margin:Number = this._margin;
        } else {
            var margin:Number = 0;
        // calculate the scaling to apply so the total inscription fits inside the rect
        // centered, with the given margin
        var clipScale:Number;
        clipScale = ((rect.width-(margin * 2)) / rect.width) * 100;
        if (this._inscriptionHeight > rect.height) {
            clipScale = ((rect.height-(margin * 2)) / this._inscriptionHeight) * 100;
        this._inscriptionClip._yscale = this._inscriptionClip._xscale = clipScale;
        this._inscriptionClip._x = (rect.width - (rect.width * (clipScale / 100))) / 2;
        this._inscriptionClip._y = (rect.height - (this._inscriptionHeight * (clipScale / 100))) / 2;
        GraphicUtil.changeColor(this._inscriptionClip, this._colorScheme.text_color);


The slabtype algorithm, Part 3: Iterative line splitting

Algorithms, Flash, Graphic Design, Interactive Design, Typography

This is the third in a four-part graphical dissection of the “slabtype” text layout algorithm I developed for Public Secrets. For an introduction to the algorithm, visit The slabtype algorithm, Part 1: Background. To review the calculations that set the stage for this post, visit Part 2: Initial calculations.

In this post, we’ll take up the real workhorse of the slabtype algorithm—iterative line splitting—followed by the final layout of the text.

Our initial calculations provided us with a single very important number: 8, our ideal character count per line. This number gives us a target to aim for as we split our text into individual lines. We start by dividing our text into its constituent words:

Word splitting

Next, we execute the following iterative sequence:

  1. Create two containers for words. One will hold the next word of the text, the other will hold the next two words of the text.
  2. Keep adding subsequent words to both containers until the character length of one container is less than or equal to the length of the ideal character count per line, while the character length of the other container is greater than the ideal character count per line.
  3. Store the contents of the container whose character count is closest to the ideal character count per line.
  4. Repeat.

Here’s a diagram of how we arrive at our first line using this sequence:

First line

In this example, our two word containers initially hold the words “I and “I WISH. Neither of these exceed the ideal character count per line, so we continue adding words, giving us “I WISH and “I WISH IT. The latter is ten characters long, two characters longer than our ideal character count per line of eight. Since the former is seven characters long, resulting in only a one-character difference between its length and the ideal, we store “I WISH as the contents as the first line of the slab.

Here’s how we arrive at the next line:

Second line

Here, we have a very similar case. Neither IT nor IT WAS exceed the ideal character count, so we proceed to IT WAS and IT WAS THAT. IT WAS is only two characters off the ideal, compared to three characters for IT WAS THAT, so we pick the former.

Third line

The third line plays out a bit differently.  With THAT and THAT SIMPLE, we find that THAT SIMPLE’s character count of eleven is nearer the target of eight than THAT’s character count of four, so we go with the latter.

The fourth line plays out much like the first two:

Fourth line

While the fifth pass chooses the first of the two text containers:

Fifth line

The sixth finds ERASE MY matching the ideal character count per line exactly:

Sixth line

Leaving PAST” as our only remaining word, which becomes a line unto itself.

Seventh line

Since we have exhausted our available words, the iterative part of the algorithm ends, resulting in our original text being split into seven lines:

All seven lines

For the final installment, we’ll turn our attention to laying out the text within the target box (source code will be provided).

Coming soon: The slabtype algorithm, Part 4: Final layout and source code


The slabtype algorithm, Part 2: Initial calculations

Algorithms, Flash, Graphic Design, Interactive Design, Typography

This is the second in a four-part graphical dissection of the “slabtype” text layout algorithm I developed for Public Secrets. For an introduction to the algorithm, visit The slabtype algorithm, Part 1: Background.

Execution of the slabtype algorithm breaks down into three phases: initial calculations, iterative line splitting, and final layout. In this post, we’ll tackle the initial calculations that set the stage for the work of the algorithm.

Three constants are used to constrain the results of the initial calculations. The first is the average aspect ratio of a single character of the font we plan to use (Alternate Gothic No. 3, in this case). This is important because it gives us a way to guess how wide a particular line of text is going to be without consuming precious time by actually laying it out. I looked at a selection of characters from the font and estimated the aspect ratio accordingly.

Average character aspect ratio

Next, I decided upon a character count for the “ideal line length” of text to be fit into the slab. Since I used the “squarified” variant of the treemap algorithm to generate the enclosing boxes, I could be confident that a fixed value would give good results, but a more truly dynamic implementation would derive the ideal line length from a pixel value for the average height or width of a single character in the ideal point size for the display.

Ideal line length, in characters

We multiply the average character aspect ratio by the ideal line length to arrive at an aspect ratio for the “ideal line”:

Ideal line aspect ratio

These constants are defined once at the beginning of the program. The calculations which follow are executed each time the algorithm is invoked.

We start with the text which the algorithm is tasked with laying out.

Source text

The algorithm is then supplied with the dimensions of the slab (box) into which the text is to be placed:

Enclosing box dimensions

We divide the width of the box by the aspect ratio of the “ideal line” of text which it is to contain, resulting in a pixel value for the height of this line.

Line height, in pixels

When we divide the height of the box by the height of the ideal line, we arrive at a hypothetical line count—an estimate of how many lines the text is going to have to be broken into to fit snugly within the box.

Hypothetical line count

Since we know the number of characters in our text, we divide it by our hypothetical line count to come up with an “ideal character count” per line of text.

Ideal character count per line

As we will see in the next part, this is a very important value—it becomes a benchmark to help us decide where to split the text into lines.

Coming soon: The slabtype algorithm, Part 3: Iterative line splitting


The slabtype algorithm, Part 1: Background

Algorithms, Flash, Graphic Design, Interactive Design, Typography

Animator/designer Alessandro Ceglia pointed out to me a few months back that it’s possible that many users of Public Secrets don’t realize that the piece’s visual presentation is almost entirely algorithmic. Once you get beyond the title screen, all visual composition is handled dynamically, and you’ll never be able to take two identical screenshots of the piece. The designer’s statement for the project describes the two main algorithms used in the project: treemaps (an existing solution dating back to 1991) and an original text-layout algorithm which as of this article is dubbed “slabtype.”

Treemaps (which I fell in love with after seeing Martin Wattenberg’s Map of the Market while I was working at Razorfish) are covered extensively elsewhere (description, history, Wikipedia) and are used to generate the overall layout of boxes for each screen of the piece. In this four-part series of posts I’m going to present a graphical breakdown of the slabtype algorithm responsible for laying out the text and quotations which appear inside the boxes (source code will be provided in the final post).

As the design process for Public Secrets began to lead Sharon Daniel and I back towards her original idea of making the treemap algorithm a central metaphor of the piece, it became clear that we could really use some aesthetically pleasing way of dynamically placing arbitrary amounts of text inside a box. Early designs organized the statements of the incarcerated women as collections of titles, but ultimately these approaches were rejected as too index-like and lacking in emotional power.

An early, more index-like design for Public Secrets.

An early, more index-like design for Public Secrets.

A subsequent design hit upon what later became our “split” view, which runs text along an arbitrary rectilinear dividing line between halves of a binary. The dividing line was shown to organize the space on either side into rectangular blocks in which text was laid out along the borders of squares. The idea was intriguing, and I started writing some pseudocode to work out how to fit the text to the border: the program would make a “best guess” at the relative point sizes needed and then refine the guess iteratively. The algorithm was never finalized, however, as it was clear that the type was too hard to read in this configuration.


The “split” view, featuring text running around the borders of boxes.

Further exploration led to a new tack in which the text associated with a particular box was chopped up and resized into a slab that approximated the shape of its enclosing rectangle. This method seemed to add an urgent quality to the quotes and supported an approach in which the quotes themselves were the primary visual experience of the piece—dovetailing nicely with Sharon’s original intent to foreground the voices of the women.

A mockup of the approach that became the model for the slabtype algorithm.

A mockup of the approach that became the model for the slabtype algorithm.

The above screen was assembled by hand in Illustrator and Photoshop, but after Sharon agreed that this approach held promise, I started working on the algorithm itself.

Next: The slabtype algorithm, Part 2: Initial calculations


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