US3761765A — Crt display system with circle drawing

Claim 1

Independent Claim 307 words

A display system of the CRT type, in which lines to be displayed are produced from signals representing the co-ordinates of points spaced along the lengths of the lines to be displayed, including means for generating signals representing the coordinates of points spaced along the lengths of a succession of adjoining straight lines each of which is of a predetermined length and at a predetermined angle such that the display produced from said signals approximates to a desired curved line; said signal generating means comprising: a. first storage means for storing in respect of each straight line information defining the difference in position of adjacent points in that straight line and hence defining the angle of that line b. second storage means for storing information defining the desired length of each straight line; c. length counting means for indicating the actual length of the straight line currently being drawn; d. comparator means, responsive to outputs from the second storage means and the length counting means, for producing an output when the line currently being drawn is of the desIred length; e. line counting means, responsive to the output of said comparator, for indicating which straight line is currently being drawn; f. co-ordinate register means for holding information defining the co-ordinates of a point; g. logic circuit means for selecting and supplying information from said first storage means to said register means in dependence on the count of said line counting means; and h. means for applying input pulses to said length counting means so that information defining the co-ordinates of each point in turn appears in said register means, in the order the points occur along said curved line, the image produced on the screen of the display device of the system being a representation of the points defined by the information appearing in said register means.

Claim 2

Dependent Claim 307 words

A display system of the CRT type, in which lines to be displayed are produced from signals representing the co-ordinates of points spaced along the lengths of the lines to be displayed, including means for generating signals representing the coordinates of points spaced along the lengths of a succession of adjoining straight lines each of which is of a predetermined length and at a predetermined angle such that the display produced from said signals approximates to a desired curved line; said signal generating means comprising: a. first storage means for storing in respect of each straight line information defining the difference in position of adjacent points in that straight line and hence defining the angle of that line b. second storage means for storing information defining the desired length of each straight line; c. length counting means for indicating the actual length of the straight line currently being drawn; d. comparator means, responsive to outputs from the second storage means and the length counting means, for producing an output when the line currently being drawn is of the desIred length; e. line counting means, responsive to the output of said comparator, for indicating which straight line is currently being drawn; f. co-ordinate register means for holding information defining the co-ordinates of a point; g. logic circuit means for selecting and supplying information from said first storage means to said register means in dependence on the count of said line counting means; and h. means for applying input pulses to said length counting means so that information defining the co-ordinates of each point in turn appears in said register means, in the order the points occur along said curved line, the image produced on the screen of the display device of the system being a representation of the points defined by the information appearing in said register means.

Claim 3

Dependent Claim 39 words

A system according to claim 1 wherein the information stored in said first and second storage means is such that the display produced from the generated signals is a substantially regular many-sided polygon and thus approximates to a circle.

Claim 4

Dependent Claim 94 words

A system according to claim 2 wherein the display produced is a polygon having an integral number of sides in each quadrant, said first storage means stores information in respect of points in the sides in one octant of the polygon; and said first storage means is connected to said register means via output circuit means for controlling the information supplied to the register means from said first storage means to obtain information defining the co-ordinates of the points in the sides of the other seven octants of the polygon in said register means.

Claim 5

Dependent Claim 87 words

A system according to claim 2 wherein said second storage means stores a number defining the radius of the circle, and second logic circuit means is provided for increasing the number of points in every side of the polygon by the same amount in response to an increase in the more significant part of the number and for increasing the number of points in a fractional selection only of the sides of the polygon in response to an increase in the less significant part of the number.

Claim 6

Dependent Claim 53 words

A system according to claim 1 wherein adjacent points in each straight line are equally spaced and second logic circuit means are provided for varying the number of points in a selection, which may be all, of said straight lines, thereby to vary the size of said curved line without altering its shape.

Claim 7

Dependent Claim 38 words

A system according to claim 4 wherein an increase in the number of points in a side of said fractional selection is effected by delaying the output of the comparator for that side by one input pulse period.

Claim 8

Dependent Claim 35 words

A system according to claim 4 wherein said fractional selection is determined by comparing said less significant part of the number stored in the second storage means and the count of said side counting means.

Claim 9

Dependent Claim 56 words

A system according to claim 1 including a deflection system associated with the display device and means for applying the output of said signal generating means to said deflection system so as to produce images on the screen of the display at positions corresponding to the points defined by the output of said signal generating means.

Claim 10

Dependent Claim 52 words

A system according to claim 1 including a deflection system for scanning the screen of the display device in a raster, and means for utilizing the output of the signal generating means to brighten-up portions of the raster lines corresponding to the points defined by the output signal of said generating means.

Claim 11

Dependent Claim 50 words

A system according to claim 9 including means for controlling the length of the brightened-up portions of the raster lines in dependence on the spacing of the points defined by the output of the signal generating means, thereby to render each straight line image of substantially the same overall brightness.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1976-09-24	1977-03-26	1977-09-25	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1980-09-24	1981-03-26	1981-09-25	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1984-09-24	1985-03-26	1985-09-25	$7700.00	Window Closed / Lapsed

Crt display system with circle drawing

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