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Chapter 4 - Font Manager / Font Manager Reference

The Bitmapped Font ('NFNT') Resource

The Offset to the Width/Offset Table

The offset to the width/offset table element of the bitmapped font resource is represented as the owtLoc field in the FontRec data type. This field defines the offset from the beginning of the resource to the beginning of the width/offset table.

The value of nDescent, when positive, is used as the high-order 16 bits in the 32-bit value that is used to store the offset of the width table from the beginning of the resource. To compute the actual offset, the Font Manager uses this computation:

actualOffsetWord := BSHL(nDescent, 16) + owTLoc;

If the value of nDescent is negative, it is still the negative of the descent measurement, as it was in the original usage of these values; however, the Font Manager no longer
uses this value.

Note

This field was originally defined as an integer value, because it was not foreseen that this value could exceed 32 KB. The negated descent element, represented in the nDescent field of the FontRec data type, was created purely for the convenience of the Font Manager. It stored the negative of the value of the descent field, which is always positive by QuickDraw convention. When the depth of fonts increased, the values of the owTLoc field had to increase, and the extra bits needed to be stored somewhere. Since the nDescent field was created as a convenience, it was a handy place to store more information.