:.· The truetype format blueprint

The TrueType format is - apart from the file format - basically the same under Windows and and MacOS. The form of appearance of a character, the so-called 'glyph', is described as a sequenz of dots on a grid. These dots can be 'on-curve' or 'off-curve'. Two on-curve dots make up a straight line (P0 and P2). A third dot outside of the line - an off-curve dot (P1) - makes a parabolic curve possible. These kind of curves are also known as square bezier curves. By moving the dots aroung on the grid the appearance of the curve can be manipulated.

By combining curves with straight lines it is possible to create complex glyphs. Fig. 2 shows on-curve (black) and off-curve (white) dots.
In relatively simple glyphs, like the one in fig. 2, the sequenz of dots defines a closed shape. More complex glyphs, like the one in fig. 3, have multiple forms which define the contour.
To describe a contour like the one shown in fig. 3 additional rules must be applied. All contours must be closed. The dots in the first contour must be numbered in ascending order, beginning with 0 (zero). Additional dots in new contours are numbered beginning with the next available number. The way in which the dots are numbered is very important, because it defines the contour's direction. A contour always runs from the smallest to the largest number. A contour's direction is needed to determine which contours must be filled (black) and which are unfilled (white).