Browse Prior Art Database

Emulating Overlapping Windows on an Alphanumeric Display

IP.com Disclosure Number: IPCOM000040225D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 25K

Publishing Venue

IBM

Related People

Anthias, T: AUTHOR [+3]

Abstract

IBM 3270 architecture display devices have the special characteristic that they require one character cell on the screen for each alphanumeric field attribute. Special algorithms for positioning the alphanumeric field attributes are therefore necessary in order to emulate overlapping windows or partitions on these devices. An algorithm is disclosed for positioning field attributes before and after alphanumeric fields which are clipped by window boundaries or overlapped by other windows. This algorithm is also extended for positioning field attributes around the alphanumeric cells which make up the borders of windows. When alphanumeric fields within an emulated partition or window are clipped or overlapped, it is necessary to generate extra field attributes around the visible part or viewport of the field.

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Emulating Overlapping Windows on an Alphanumeric Display

IBM 3270 architecture display devices have the special characteristic that they require one character cell on the screen for each alphanumeric field attribute. Special algorithms for positioning the alphanumeric field attributes are therefore necessary in order to emulate overlapping windows or partitions on these devices. An algorithm is disclosed for positioning field attributes before and after alphanumeric fields which are clipped by window boundaries or overlapped by other windows. This algorithm is also extended for positioning field attributes around the alphanumeric cells which make up the borders of windows. When alphanumeric fields within an emulated partition or window are clipped or overlapped, it is necessary to generate extra field attributes around the visible part or viewport of the field. The field attribute is generated in the screen position before each visible part of the field, and a base protected attribute is generated in the screen position after each visible part of the field. These are called start and end attributes, respectively. To avoid conflict between start and end attributes of fields in adjacent or overlapping partitions or viewports, and to minimize the number of screen positions used for these extra attributes, the following algorithm is used to determine if and where to place the attributes. 1.If the position on the screen (wrapping round, if necessary) immediately before a visible portion of a field is of higher viewing priority than the partition to which the field belongs, then the start attribute is placed in the first visible byte; otherwise, it is placed at the screen position before this. 2.If the position on the screen immediately after a visible portion of a field is of higher viewing priority than the partition to which the field belongs, then the end attribute is placed in the last visible byte; otherwise, it is placed in the screen position after this. 3.In addition to (2), end attributes will not be generated if they overlay start attributes, as start attributes have priority. 4. This algorithm is implemented efficiently by means of a control block, ca...