Device for forming a circular image on a display screen

Details Device for forming a circular image on a display screen Device for forming a circular image on a display screen

1992-11-09

1995-01-31

Nguyen, Phu K.

G06F 1560

Patent

active

053865014

ABSTRACT:
A display screen (3) is scanned in a pattern of parallel image lines, each extending in conformity with the equation y=Y.sub.L in a rectangular system of coordinates associated with the display screen, Y.sub.L having a different value for each image line, and an output signal is formed at any instant at which an image line intersects the circumference of a desired circle (31) to be formed bounding the image. The device includes a first store (13) for coordinates X.sub.r, Y.sub.r of at least one quadrant of a reference circle (27) having a predetermined centre M.sub.0 (X.sub.0, Y.sub.0) and a predetermined radius R.sub.r, the Y.sub.r coordinate acting as an address, the associated X.sub.r coordinate being stored at each address Y.sub.r, respectively; an arithmetic device (15) for calculating the coordinates X', Y' of the desired circle (31) from the coordinates X.sub.r, Y.sub.r of the reference circle (27) and given values of the radius R and the coordinates X.sub.1 , Y.sub.1 of the centre M.sub.1 of the desired circle; a second store (19) for the calculated values of X' and Y', the calculated values Y' acting as addresses, the associated values of X' being stored at each address Y'; and a comparator (23) for comparing, during the scanning of the display screen (3), the x-coordinates followed during the formation of each image line y=Y.sub.L m with the value X' associated with Y'=Y.sub.L and stored in the second store, and for generating an output signal at the instant at which x=X'.

REFERENCES:
patent: 5265197 (1993-11-01), Kondo

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