GB1442544A - Apparatus for use in character generation - Google Patents

Abstract

1442544 Character generator ROCKWELL INTERNATIONAL CORP 16 April 1974 [11 May 1973 (2)] 16530/74 Heading G4A A character generator, by executing a program of instructions individual to a character to be displayed, establishes, for each successive value of one co-ordinate in a two co-ordinate system, values of the other co-ordinate representing the initial and terminal points of a section of the character along the particular value of the one co-ordinate. The generator may be used in conjunction with a CRT whose beam is alternately unblanked and blanked at successive ones of generated Y coordinate values during its Y scan at each successive X co-ordinate value, the Y values being computed during the preceding scan. The program defines the character in its maximum size, scaling factors being used to display smaller sizes. An exemplary program is shown in Fig. 3B to develop the character of Figs. 3A and 3C. The instructions are taken in sequence, each instruction being started at a cycle determined by a value in the preceding instruction and all instructions being executed in each successive cycle until cancelled (EOLP) or replaced by a later instruction. The allowable instructions include BOLP instructions which establish initial Y values for a pair of outlines, e.g. 1 and 2, Fig. 3C, defining the initial and terminal point of a section of the character. The Y values are stored in increasing value in a circulating store together with an identification of which outline they relate to and are compared with the current Y value of the beam position to control unblanking and blanking of the beam. Slope instructions CM establish a slope for a specified outline by specifying a Y increment (or decrement) which is used to modifiy the current Y value for the next scan, the increments (and decrements) being read from an R.O.M. by coded signals M in the instruction. Change slope instructions CK progressively modify the slope as the current X value increases, each slope being maintained for a number of cycles (X values) determined by values read from an R.O.M. so as to match the outlines traced to a curve more closely. EOLP instructions delete the Y values for specified pairs of outlines and an EC instruction deletes all Y values, terminating the display. The Specification describes the system in some detail, specifying the R.O.M. contents and the way in which they are arranged and used so as to reduce the amount of storage required.