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Chapter 4 - Font Manager / Font Manager Reference

The Font Family ('FOND') Resource

The Font Family Kerning Table

The font family kerning table consists of a group of kerning subtable entries. Each subtable contains the measurements of a hypothetical 1-point font of this family with a different stylistic variation. The Font Manager multiplies these measurements by the requested font size. The structure of the font family kerning table is shown in Figure 4-29.

Figure 4-29 The font family kerning table

The font family kerning table is represented by the KernTable data type, which is shown on page 4-45. It consists of a count, followed by a variable number of kerning subtable entries.

• Number of entries. This is an integer value that specifies the number of kerning subtable entries in this table minus 1. This value is represented by the numKerns field of the KernTable data type.

Each kerning subtable entry is represented by the KernEntry data type, which is described on page 4-45. Each subtable pertains to a specific style code and contains a variable number of kerning pair entries. The style code values are shown in Figure 4-23 on page 4-89. The elements of each subtable entry are as follows:

• Kern style. This is an integer value that specifies the style code to which the kerning information in the subtable pertains. This value is represented by the kernStyle field of the KernEntry data type.
• Entry length. This is an integer value that specifies the number of bytes in this kerning subtable. This value is represented by the kernLength field of the KernEntry
  data type.

Each kerning pair entry specifies a kerning distance in pixels for a pair of glyphs. Each glyph is specified by its character code. The structure of the kerning pair entry is shown in Figure 4-30.

Figure 4-30 A kerning pair entry

Each kerning pair entry is represented by the KernPair data type, which is shown on page 4-45. The elements of each entry are as follows:

• First character code. The one-byte character code of the first glyph of the kerning pair. This value is represented by the kernFirst field of the KernPair data type.
• Second character code. The one-byte character code of the second glyph of the kerning pair. This value is represented by the kernSecond field of the KernPair data type.
• Kerning distance. The kerning distance, in pixels, for the two glyphs at a point size of 1. This is a 16-bit fixed point value, with the integer part in the high-order 4 bits, and the fractional part in the low-order 12 bits. The Font Manager measures the distance in pixels and then multiplies it by the requested point size. This value is represented by the kernWidth field of the KernPair data type.