libtypeset is a C++ library that aims at providing an abstract layouting engine
suitable for typesetting complex documents.
The library is heavily inspired by TeX, the typesetting system designed by Donald Knuth. It currently implements many of the primitives present in the language including boxes, glue, kerns and penalties.
The Qt framework is used to provide some examples of typesetting text.
Albeit being extremely simple, the concepts of boxes and glue turn out to be also incredibly powerful. They make text justification an easy task while also allowing particular spacing rules out of the box.
The following picture shows how a single line of text can be rendered on pages with different width. First the line is rendered on its ideal page width, then the page width is increased respectively by 15% and 25%.
Notice how the spacing rules are different after a comma or a period. Here, the interword space increase 50% faster after a comma and 100% faster after a period, hence making the space after a period almost twice as large as a regular space.
libtypeset also provides a basic implementation of TeX linebreaking algorithm.
This algorithm is used to break a paragraph of text into a series of line.
Unlike a naive algorithm which would consider each line independently, TeX linebreaking algorithm considers the paragraph as a whole to produce more aesthetic results. Indeed, the basic strategy that consists of filling a line with as much text as possible and then going to the next line may produce lines with too few words that will look bad. TeX tries to avoid such situations by sometimes putting fewer words than possible on a line to make the next lines look better. The whole process is in fact an optimisation problem: the algorithm tries to minimise a cost (in the context of TeX, this cost is called the demerit).