Little improvements on pulse.el

[Gabriel <gabriel376@hotmail.com>]

I have been playing with pulse.el in the last few days and some
ideas/questions come to my mind.

This is the current source code of 'pulse-line-hook-function':

(defun pulse-line-hook-function ()
  "Function used in hooks to pulse the current line.
Only pulses the line if `pulse-command-advice-flag' is non-nil."
  (when pulse-command-advice-flag
    (pulse-momentary-highlight-one-line (point))))

1. It can be useful in some cases to pulse the current line by using an
interactive command, for example, when doing a presentation, a pairing
with other developer, or to easily find the cursor position. Since
'pulse-line-hook-function' is not a good name for an interactive
function, we can create a new command for that.

2. The name and the docstring mention the use with hooks, but would be
nice to use with advices as well. For example, to highlight the current
line when the cursor, buffer or window changes:

(dolist (symbol '(scroll-up-command
                  scroll-down-command
                  recenter-top-bottom
                  other-window
                  windmove-do-window-select
                  kill-current-buffer
                  delete-window))
  (advice-add symbol :after #'pulse-line-hook-function))

The code above does not work, since 'pulse-line-hook-function' does not
accept any argument (sent by the advice function). We can make it accept
optional arguments, but again the name will not be the best one.

3. I could not find any documentation or usage in emacs source code for
'pulse-line-hook-function' and 'pulse-command-advice-flag'. Is the flag
'pulse-command-advice-flag' really needed ? The git history says the
last modification of this code was 12+ years ago.

4. Would be nice to have support for 'pulse-highlight-start-face' in the
themes provided by Emacs, especially on modus-themes.

5. The code on 'pulse-lighten-highlight' can be significantly improved
by replacing 'pulse-int-to-hex' and 'pulse-color-values-to-hex' with
'color-gradient' from color.el. The idea is to build the list of color
gradients beforehand and use a timer to set each color according to
'pulse-iterations' and 'pulse-delay'. A very basic example:

(let* ((start (color-name-to-rgb (face-background 'pulse-highlight-start-face)))
       (end (color-name-to-rgb (face-background 'default)))
       (gradient-rgb (append (list start)
                             (color-gradient start end pulse-iterations)
                             (list end)))
       (gradient-hex (mapcar (apply-partially 'apply 'color-rgb-to-hex) gradient-rgb)))
  (seq-do-indexed (lambda (color index)
                    (run-with-timer (* index pulse-delay)
                                    nil
                                    (apply-partially 'funcall
                                                     (lambda (color)
                                                       (set-face-background 'default
                                                                            color))
                                                     color)))
                  gradient-hex))

Please share your comments and suggestions. I have FSF copyright
assignment and can open patches for these (or other) improvements/bugs.

Regards,
Gabriel