Fonts & Encodings

Appendix E. TrueType Instructions

TrueType instructions have the same purpose as PostScript hints: the optimization of the bitmap rasterization of glyphs. That is why people often speak of "TrueType hints"—a false term that loses the meaning of "hint", which is "indication", "suggestion". There is a fundamental difference between the strategies for optimizing rasterization that the PostScript and TrueType fonts use. In the former, the font's designer gives a few indications to the PostScript interpreter, in the hope that his wishes will be granted. What he provides are nothing but indications: a few relevant dimensions, such as the height of the lowercase letters and the thickness of the strokes, and a few strokes that he would like to have rendered in the same way. These data are supplied to the "black box" that is the interpreter, and one can only hope that they will be used appropriately. But there is no guarantee as to the final result—only the promises of Adobe, balanced by a few arguments such as "if you give us the correct hints, we'll give you a good optimization", which could also be interpreted as "if the optimization is poor, the hints you gave us were incorrect; don't blame us!"

TrueType's strategy is different: one provides some clear and precise instructions to the TrueType processor and expects that they will be applied. A set of instructions is a program, written in a syntax similar to assembly language. This approach is also more democratic, since anyone can write ...