Raster, Vector, and TrueType® Fonts

Windows-based applications can use three different kinds of font technologies to display and print text: raster, vector, and TrueType. The differences between these fonts reflect the way that the glyph for each character or symbol is stored in the respective font-resource file. In raster fonts, a glyph is a bitmap that Windows uses to draw a single character or symbol in the font. In vector fonts, a glyph is a collection of line endpoints that define the line segments Windows uses to draw a character or symbol in the font. In TrueType fonts, a glyph is a collection of line and curve commands as well as a collection of hints. Windows uses the line and curve commands to define the outline of the bitmap for a character or symbol in the TrueType font. Windows uses the hints to adjust the length of the lines and shapes of the curves used to draw the character or symbol. These hints and the respective adjustments are based on the amount of scaling used to reduce or increase the size of the bitmap.

Because the bitmaps for each glyph in a raster font are designed for a specific resolution of device, raster fonts are generally considered to be device dependent. Vector fonts, on the other hand, are not device dependent, because each glyph is stored as a collection of scalable lines. However, vector fonts are generally drawn more slowly than raster or TrueType fonts. TrueType fonts provide both relatively fast drawing speed and true device independence. By using the hints associated with a glyph, a developer can scale the characters from a TrueType font up or down and still maintain their original shape.

As previously mentioned, the glyphs for a font are stored in a font-resource file. A font-resource file is actually a Windows library that contains only data ¾ there is no code. For raster and vector fonts, this data is divided into two parts: a header describing the font's metrics and the glyph data. A font-resource file for a raster or vector font is identified by the .FON filename extension. For TrueType fonts, there are two files for each font: the first file contains a relatively short header and the second contains the actual font data. The first file is identified by a .FOT extension and the second is identified by a .TTF extension.