Browse Prior Art Database

Fractional Scaling of Integer Vectors

IP.com Disclosure Number: IPCOM000043188D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 1 page(s) / 13K

Publishing Venue

IBM

Related People

Berghorn, CR: AUTHOR [+2]

Abstract

Vectors representing X-Y positions on a graphic display screen can be scaled by non-integer values. Coordinate values representing points on the screen of a computer graphics display device are usually represented by integers, and data to be displayed are usually represented by sets of coordinate values. A line is represented by the coordinates of its two endpoints. A line may be scaled (magnified or reduced in size) by multiplying its length by the desired scaling factor and using the product to compute a new endpoint. This is most usually done by multiplying the individual X- and Y-axis delta values by the scaling factor.

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Fractional Scaling of Integer Vectors

Vectors representing X-Y positions on a graphic display screen can be scaled by non-integer values. Coordinate values representing points on the screen of a computer graphics display device are usually represented by integers, and data to be displayed are usually represented by sets of coordinate values. A line is represented by the coordinates of its two endpoints. A line may be scaled (magnified or reduced in size) by multiplying its length by the desired scaling factor and using the product to compute a new endpoint. This is most usually done by multiplying the individual X- and Y-axis delta values by the scaling factor. Scaling by integer multipliers is easily accomplished with inexpensive logic circuits; however, scaling by non-integers generally requires either analog scaling techniques or a floating-point processor within the display station, or else it is done in the host computer system before the X-Y values are transmitted to the display station. This invention provides a simple, fast and inexpensive means of doing this function within the display station. In the IBM 3277 Graphics Attachment (GA), point coordinates are pairs of 12-bit binary values in the range 0-4095 decimal. A six-bit scaling factor is supported, providing scaling multipliers in the range 0-63 decimal. Because the X value and Y value are specified at different points in time, a single 6 x 12-bit multiplier serves as a vector scaler in the 3277GA. Two factors limit the usefulness of integer scaling: the size of the smallest vector increment before scaling, and the visual resolution of the display screen upon which the vectors are to be displayed. If the smallest increment is substantial relative to the smallest visible unit, then the usable range of scaling factors is limited, and only the smaller values will be used. In the 3277G...