Feature-Based Design of Fonts Using Constraints - CiteSeerX

Feature-Based Design of Fonts Using Constraints Ariel Shamir and Ari Rappoport Institute of Computer Science, The Hebrew University, Jerusalem 91904, Israel. http://www.cs.huji.ac.il/ arik arir , arik—arir @cs.huji.ac.il

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Abstract. Computer-aided font design is still a very tedious and repetitive task. New font models and new functionalities presented by digital media further require a new method for design of font families and dynamic variable fonts. Current design paradigms are either outline based, offering low level operations, or parametric but non-visual programming. Parametric feature based design helps in creating a design environment for high level parametric font design. However, the approaches suggested so far are too restrictive in their definition of features, and none of them utilises constraints in feature definition and design. We present a new approach for parametric feature based font design. Our approach extends the definition and use of features by defining implicit feature parts using constraints. Furthermore, the visual design system and the use of constraints for preserving designer’s intentions create a more natural environment in which high level parametric behaviors can be defined. This simplifies design of single fonts and also enables the simultaneous design of font families through parameterization.

1 Introduction Computer-aided design tools for typographers and font designers have been created as early as the 1960s [17]. Nonetheless, to date, font design systems allow mostly low level outline based manipulation of shapes, and the design process of a whole font is still a very tedious and repetitive task. New developments [2, 4] enable the wrapping of several font families in one font model. This complicates the design process even further, as the need for simultaneous design of a whole family of fonts arises. Solutions for designing families of geometric objects make use of parametric tools and constraints [18]. Advanced parametric and feature based design frameworks for fonts have been proposed (Section 2), but have failed to gain acceptance among the designer community either because they were non-visual, or because the definition and usage of features had been too restrictive. Moreover, none of the font design frameworks presented so far has used constraints in the context of a visual direct manipulation tool. With the advent of new electronic media like web pages, CD-roms and hypertext files, new challenges are posed for fonts functionality. Fonts should allow shape variations and manipulation through high level parametric operations. They should no longer be a static object and should gain a more dynamic, lively nature. Designing such fonts is a completely novel task for typographers, and the form of design tools for this kind of design process is yet to be developed. In this work we present a new approach for parametric feature based design of fonts. In contrast to previous programmable parametric models [13, 22], our system is

visual in nature and gives the designer direct manipulation capabilities. In contrast to previous feature based models [7, 1, 14] our notion of a feature is extended by the usage of constraints. Our approach creates a more natural and effective design environment for classic font design, for font families design and for dynamic or parametric font design. A review on different font design paradigms and their limitations is given in Section 2. In Section 3 we portray the guidelines of our approach to font design. Section 4 describes all components of our system and their implementation. We present two applications of our approach: in Section 5 application for font families design, and in Section 6 application for oriental font design.

2 Font Design Paradigms There are two different methods to create a digital representation of a font [3]. The first is by acquiring existing external designs using digitisation or some auto-tracing mechanism [9, 12]. This means the design itself has been done manually sometime previous to the use of the computer. This method is of special importance as a mean to import the wealth of typefaces available in traditional forms. The second method of creating digital fonts is to use the computer as a tool for designing the letter shapes themselves. These tools fall into one of several categories: visual direct manipulation tools, programmable tools and parametric features tools.

2.1 Visual Direct Manipulation Design Tools The importance of direct visual feedback in design cannot be overestimated. Designers think visually and prefer to act directly on their design objects. Both high-end and lowend visual direct font design tools are available on the market and inside commercial companies (e.g. Ikarus, FontStudio, Typo, FontLab, Fontographer) and they present different levels of functionality and quality. Still, the fact that the end product of all of them is an outline font [2, 15] affected most of them to be outline based tools. Such tools give the user the ability to create and manipulate lines and curves by adding, deleting or moving points which define splines of various types. Most of the splines used give direct manipulation capabilities and natural control over the shape of the spline, allowing very fine adjustments to the contours of the outline (see Figure 1). However, using the underlying outline model also affected systems not to use feature based or hierarchical design, and therefore, important typographic elements and glyph parts are indistinguishable. This means much of the typographic information or nature of the designed object cannot be used. Most systems also lack any mechanism for carrying design information or gestures from one glyph part to another or across the font. This means corrections to the same part of glyphs must be done over and over again, and there is no global control of font values. Lastly, there is no support for the creation of parametric or dynamic variations of the design. Exploring design space in search of possible new forms or shapes becomes a tedious process, and designing families of fonts or dynamically changing fonts is practically impossible.

Fig. 1. Example of direct manipulation of design using outline operations in a visual font design system (Fontographer).

mode_setup; thin#:=.5pt#; thick#:=1.1pt#; u#:=.6pt#; ht#:=7pt#; slab#:=.25pt#; jut#:=.9pt#; bracket#:=1pt#; serif_darkness:=1/3; def serif(suffix $) (expr breadth, theta, left_jut, right_jut) = penpos$(breadth/abs sind theta, 0); z$a - z$l = z$f - z$r = (bracket/abs sind theta) * dir theta; y$c=y$d; y$b=y$e=y$; y$b-y$c=if theta