In this paper we present a dynamic font model, LiveType, that supports complex non-linear dynamic behaviours of letter shapes. Inherent typographic and stylistic constraints are preserved during dynamic behaviour. The capability of modifying letter shapes through parameter specification is present in the font itself and is provided to any user of the font.
LiveType is implemented using parametric features and constraints. The constraints evaluation algorithm operates in linear time in the size of a glyph and guarantees finding a single solution. Constraints are represented using a special novel type of constraints graph, a mixed ratio graph, which can deal with most constraints cycles of the kind arising in the font domain. In addition, a novel constraint state machine enables modification of the shape's underlying topology during dynamic behaviour.