Browse Prior Art Database

Continuous Angle and Distance Graphics Display

IP.com Disclosure Number: IPCOM000046176D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 21K

Publishing Venue

IBM

Related People

Halliwell, H: AUTHOR

Abstract

Because of the time required for calculations, a digital read-out of the distance and direction traversed by a light pen on a refreshed display is not available until the light pen reaches its destination. This describes a technique for a continuous updating of the angle and distance traveled while the light pen is moving.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 57% of the total text.

Page 1 of 2

Continuous Angle and Distance Graphics Display

Because of the time required for calculations, a digital read-out of the distance and direction traversed by a light pen on a refreshed display is not available until the light pen reaches its destination. This describes a technique for a continuous updating of the angle and distance traveled while the light pen is moving.

The usual calculation of the distance and angle traversed by a light pen in a graphics system is performed by the host computer after an interrupt to perform the calculation. This interrupt occurs when the light pen reaches its final point. Such a process is too slow to permit the parameters to be continuously displayed during the light pen tracking. By the following method, these parameters can be determined directly in the display processor, i.e., a microprocessor dedicated to controlling the display, so that the read-out can be updated each refresh cycle without interrupting and delaying the host computer.

The method involves executing a single iteration of a Newton- Raphson approximation every refresh cycle of the display. In the first step, the absolute screen coordinates are updated by the light pen tracking system and converted to application coordinates based on parameters written by the host computer into the display buffer work space. The orthogonal displacements, dx and dy, from a fixed reference point (also written in the work space) are determined by subtraction. The maximum of dx and...