free openSS

26 ❘ FREE/OPEN SOURCE SOFTWARE: LOCALIZATIONAnti-aliasing, capability of the rasterizer to simulate unfitted pixels with some illusion to humanperception, such as using grayscales and coloured-subpixels, resulting in the feeling of “smoothcurves.”These can improve the quality of vector fonts at small sizes. Moreover, the need for bitmap fonts inmodern desktops is gradually diminishing.Font FormatsCurrently, the X Window system for GNU/Linux desktop supports many font formats.BDF FontsBDF (Bit-map Distribution Format) is a bitmap font format of the X Consortium for exchanging fonts in aform that is both human-readable and machine-readable. Its content is actually in plain text.PCF FontsPCF (Portable Compiled Format) is just the compiled form of the BDF format. It is binary and thus, onlymachine-readable. The utility that compiles BDF into PCF is bdftopcf. Although BDF fonts can be directlyinstalled into the X Window system, they are usually compiled for better performance.Type 1 FontsType 1 is a vector font standard devised by Adobe and supported by its Postscript standard. So it is wellsupported under most UNIX and GNU/Linux, through the X Window system and Ghostscript. Therefore,it is the recommended format for traditional UNIX printing.TrueType FontsTrueType is a vector font standard developed by Apple, and is also used in Microsoft Windows. Its popularityhas grown along with the growth of Windows. XFree86 also supports TrueType fonts with the help of theFreeType library. Ghostscript has also supported TrueType. Thus, it becomes another potential choice forfonts on GNU/Linux desktops.OpenType FontsRecently, Adobe and Microsoft have agreed to create a new font standard that covers both Type 1 andTrueType technologies with some enhancements to cover the requirements of different scripts in theworld. The result is OpenType.An OpenType font can describe glyph outlines with either Type 1 or TrueType splines. In addition,information for relative glyph positioning (namely, GPOS table) has been added for combining marks tobase characters or to other marks, as well as some glyph substitution rules (namely, GSUB table), so thatit is flexible enough to draw characters of various languages.Output MethodsOutput method is a procedure for drawing texts on output devices. It converts text strings into sequencesof properly positioned glyphs of the given fonts. For the simple cases like English, the character-toglyphmapping may be straightforward. But for other scripts the output methods are more complicated.Some could be with combining marks, some written in directions other than left-to-right, some withglyph variations of a single character, some requiring character reordering, and so on.With traditional font technologies, the information for handling complex scripts is not stored in thefonts. So the output methods bear the burden. But with OpenType fonts, where all of the rules are stored,the output methods just need the capability to read and apply the rules.Output methods are defined at different implementations. For X Window, it is called X Output Method(XOM). For GTK+, it uses a separate module called Pango. For Qt, it implements the output method bysome classes. Modern rendering engines are now capable of using OpenType fonts. So, there are twoways of drawing texts in output method implementations. If you are using TrueType or Type 1 fonts andyour script has some complications over Latin-based languages, you need to provide an output methodthat knows how to process and typeset characters of your script. Otherwise, you may use OpenTypefonts with OpenType tables that describe rules for glyph substitution and positioning.