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Special Glyphs

NSFont defines two special glyphs. NullGlyph indicates no glyph at all and is useful in some layout methods for calculating information that isn’t relative to another glyph. For example in Objective-C, with positionOfGlyph:precededByGlyph:isNominal:, you can specify NSNullGlyph as the first argument to get the nominal advancement of the preceding glyph.

The other special glyph is ControlGlyph, which the text system maps onto control functions such as linefeed and tab. This glyph has no graphic representation and has no inherent advancement of its own. Instead, the text system examines the control character underlying the glyph to determine what kind of special layout it needs to perform.

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