Lem's displaying concepts

Lem has some concept for displaying. This document is a result of a survey about them.

Logical concept for physical displaying areas dealt by frontends; like ncurses, electron and so on. So display has no data representation in source codes, it appears as a word. (For now) there is one display per one frontend. Lem doesn’t touch displays directly but touch these via method like lem-if:display-width.

Source (for instance): /frontends/ncurses/ncurses.lisp

UI parts like minibuffers or popup windows or normal buffers, in the display(s?). They’re defined in each frontend and Lem doesn’t touch them directly.

Source (for instance): /frontends/ncurses/ncurses.lisp

Lem’s low-level displaying area. Each screens correspond to its view. Each screen has its position and size, and may have modeline.

Source: /lib/core/interface.lisp

Lem’s displaying area. Windows have its screen, buffer and view-point (maybe viewport).

Split area is implemented with windows and window-node structure. window-node has split type (:hsplit and :vsplit), car and cdr. Root area is stored in *window-tree* special variable. *window-tree* may be an window or an window-node, by which Lem manages nest of displaying area. If it’s an window-node it means Lem’s displaying area is splitted, when its child (car or cdr) is an window-node that child area is also splitted, and so forth…

Source: /lib/core/window.lisp

Frames are the concept and the structure that represent whole window configuration in a display. It is introduced by this pull-request https://github.com/cxxxr/lem/pull/500 .

Note the special variable lem::*display-frame-map*. This mapping correspond from display-thing (for now, it’s lem:implementation) to a frame. It is for multi frame support in the near future.

Source: /lib/core/frame.lisp

The name frame appears some place of /lib/core/window.lisp as arguments of adjust-windows. This function seems to do a process when frame size is changed, e.g. terminal resizing. In this case, frame means a display described above.

Virtual frames are introduced by frame-multiplexer (called “fm-mode” at this PR). Because, in frame-multiplexer, it is needed to store frames and to switch between them. One virtual frame store multiple frames in it, and modify lem::*display-frame-map* when like frame switching.

Source: /lib/core/frame-multiplexer.lisp