Patent GB-1292327-A (GB)
Title: An apparatus for use in visual data presentation to generate area elements having a certain structure
Inventor: ERIKSSON ERIK ARVID RUNE
IPC: G09G1/10
Filed: 1969-10-20
Abstract: 1292327 Cathode-ray tube displays E A R ERIKSSON and OLE NILSSON 20 Oct 1969 [24 Oct 1968] 51355/69 Heading H4T In graphic display apparatus area elements are produced having a required structure, i.e. "shading", by filling-in the areas with, e.g. parallel lines, dots &c. of a required density, intensity, shape or colour, the positions and lengths of the lines being determined in accordance with supplied data specifying the edge of area. The area is thus produced by the shading lines without a separate reproduction of the edge or periphery of the area. The invention is described in connection with a cathode-ray tube display but is stated to be applicable to display arrangements in which a light beam is caused to move over a photographic film according to a desired pattern. The embodiment described is concerned with shading the trapezoidal area element shown in Fig. 3 by filling-in with a plurality of vertical lines spaced by a distance D. The corners of the element are defined by the co-ordinate expressions: where the sign of # 1  and # 2  can be positive or negative and such co-ordinate values together with the value D specifying the spacing of the vertical lines and a quantity L specifying the number of such lines are utilized to determine the lengths and positions of the lines. In the operation of the invention successive values of the Y-co-ordinates are compared with the vertical deflection waveform during a horizontal (X-deflection) period and equality between the compared quantities is employed to produce beam intensity control pulses which switch the beam on for the duration of the tracing of each vertical shading line. Referring to Figs. 1 and 2, the co-ordinate values Y 0  and # 1  are set up in respective registers 28, 29 of a control voltage source 15 and the coordinate values Y 0 +# 3 and # 2  are set up in corresponding registers 28, 29 of an identical control voltage source 14. The outputs of registers 28 are supplied via D/A converters 30 to adders 32 and the outputs of registers 29 are supplied via D/A converters 31 and switches 33 (closed during operation) to integrators 34. The latter are e.g. of the capacitive type and produce an output comprising an exponentially varying D.C. voltage the inputs from the D/A converters 31 being at a high level so that the portion of the integrator outputs which is utilized (i.e. the first portion) is substantially linear. Such outputs are combined with the outputs of the D/A converters 30 in adders 32 which supply respective sampling circuits 35 and from which samples are periodically derived and supplied to a comparator 12 which also receives the vertical deflection waveform U y  from generator 10. The horizontal deflection U x  is produced by an arrangement 18 comprising registers 37, 38 in which the co-ordinate value X 0  and the spacing dimension D are respectively stored, the arrangement operating in response to pulses U 13  from a gate 20 to supply horizontal step deflections to the display tube 11 via a D/A converter 39. The quantity L defining the total number of lines is set up in a counter 22 and this is counted down to zero by the pulses from gate 20. These pulses U 13  which also act as sampling pulses for the samplers 35 are produced by a comparator 13 when equality is reached between the input vertical deflection waveform and lower and upper reference voltages U A , U B  from sources 16, 17, these voltages being set such that the spacing between the pulses U 13  remains constant. When a display is to be produced the circuit is "cleared" either by an output pulse which is produced by counter 22 at the termination of the last display operation or by a pulse supplied to terminal 25 either of which operates via OR gate 24 to close gates 20 and 21, to set a beam control flip-flop 40 such that the beam of tube 11 is blanked and to open switches 33. A start signal U s  is then supplied to terminal 27 which acts via AND gate 26, on the occurrence of the next pulse U 13  from comparator 13, to close the switches 33 and to open gate 21. The latter then passes pulse U 12  derived from comparator 12 on the first coincidence of the vertical deflection waveform and the sample input and the pulses U 12  open gate 20 and trigger flip-flop 40 such that the beam is unblanked. The latter then commences to trace a vertical line which is terminated by the next pulse U 12  produced by comparator 12 on the second coincidence between the vertical deflection waveform and the sample input, such pulse changing flip-flop 40 back to its initial (beam blanked) state. Thus a succession of beam unblanking pulses U i  is produced whilst the beam is moving between the positions determined by coincidence of the vertical deflection waveform and the sample values U M , U N  as shown in Fig. 2, and when all the lines have been produced the output from counter 22 closes gate 20 to terminate the horizontal deflection, ensures that the beam control flip-flop 40 blanks the beam and opens switches 33. Areas of other shapes may be produced by dividing them into sub-areas of trapezoidal or triangular shapes, the shading lines may be horizontal instead of vertical, the width of the lines may be varied by changing the intensity and focusing of the beam or by noise modulation of the horizontal deflection and dashed lines may be produced by pulse modulation of the beam intensity.