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);


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