Beschreibung:
<jats:p>One of the common uses of bitmap terminals is storing multiple programming contexts in multiple, possibly overlapping, areas of the screen called windows. Windows traditionally store the visible state of a programming environment, such as an editor or debugger, while the user works with some other program. This model of interaction is attractive for one-process systems, but to make full use of a multiprogramming environment, windows must be asynchronously updated, even when partially or wholly obscured by other windows. For example, a long compilation may run in one window, displaying messages as appropriate, while the user edits a file in another window.</jats:p>
<jats:p>
This paper describes a set of low-level graphics primitives to manipulate overlapping asynchronous windows, called
<jats:italic>layers,</jats:italic>
on a bitmap display terminal. Unlike previous window software, these primitives extend the domain of the general bitmap operator
<jats:italic>bitblt</jats:italic>
to include bitmaps that are partially or wholly obscured.
</jats:p>