An Algorithmic Interpretation of the GKS TEXT Primitive

Abstract

The specification of text output is one of the most complex parts of the GKS standard [1]. The text “geometry” is determined by a wide variety of factors: some, such as character height, are specified directly by the user; others, such as the aspect ratio of a character in a given font, are characteristic of a particular implementation. The GKS document gives a detailed, but informal, description of the way in which these various factors combine to determine the text size and position. The purpose of this paper is to put forward a more formal description of the GKS text geometry: an algorithm is presented that calculates the size and positions of individual character bodies for any text string, under any setting of text attributes, together with the text extent rectangle and concatenation point; a realization of the algorithm as a FORTRAN 77 subroutine is also given. It is hoped that the algorithm will help implementos to interpret the GKS standard more easily.