branch: externals/coterm
commit db17a99f2a4393e2a836102259b024732609d285
Author: m <>
Commit: m <>
Describe terminal emulation
---
coterm.el | 35 +++++++++++++++++++++++++++++++++++
1 file changed, 35 insertions(+)
diff --git a/coterm.el b/coterm.el
index 2edd904..340548b 100644
--- a/coterm.el
+++ b/coterm.el
@@ -61,6 +61,15 @@
;; ;; Optional: bind `coterm-char-mode-cycle' to C-; in comint
;; (with-eval-after-load 'comint
;; (define-key comint-mode-map (kbd "C-;") #'coterm-char-mode-cycle))
+;;
+;;
+;; Differences from M-x term:
+;;
+;; coterm is written as an upgrade to comint. For existing comint users, the
+;; behaviour of comint doesn't change with coterm enabled comint except for the
+;; added functionality that we can now use TUI programs. It is therefor good
+;; for users who generally prefer comint to term.el but sometimes miss the
+;; superior terminal emulation that term.el provides.
(require 'term)
(eval-when-compile
@@ -438,6 +447,32 @@ is the process mark."
;;; Terminal emulation
+;; This is essentially a re-implementation of term.el's terminal emulation. I
+;; could have simply reused functions from term.el but that would have been
+;; unsatisfactory in my opinion. That is mostly due to the fact that term.el's
+;; terminal emulation inserts a lot of redundant trailing whitespace end empty
+;; lines, which I believe is very distracting for ordinary comint usage.
+;;
+;; Terminal emulation is coordinate based, for example, "move cursor to row 11
+;; and column 21". A coordinate position may not be reachable in an Emacs
+;; buffer because the specified line is currently too short or there aren't
+;; enough lines in the buffer. term.el automatically inserts empty lines and
+;; spaces in order to move point to a specified coordinate position. This
+;; results in trailing whitespace.
+;;
+;; coterm takes a different approach. Instead of moving point, the current
+;; terminal cursor coordinates are kept in the variables `coterm--t-row' and
+;; `coterm--t-col'. Moving the terminal cursor simply means adjusting these
+;; two variables, no whitespace needs to be inserted. Point and process mark
+;; are usually not guaranteed to be anywhere near the current coordinate
+;; position and are only restored at the end of the main filter function
+;; `coterm--t-emulate-terminal'. Only when terminal emulation requires
+;; insertion of actual text do we have to be able to reach the current cursor
+;; coordinates. We may have to insert newlines and spaces to make this
+;; position reachable, but inserting text after this whitespace means that it
+;; isn't trailing or redundant (except if the inserted text consists of only
+;; whitespace).
+
(defconst coterm--t-control-seq-regexp
;; Differences from `term-control-seq-regexp':
;;
