Introduce analogue clock time icon

With the SVG library (bundled as part of Emacs), we can generate an
analogue clock for the current time to-the-minute, instead of using the
nearest-hour nerdicon.

This relies on a graphical display, and so a new variable is introduced,
`doom-modeline-time-analogue-clock' and the behaviour is gated
on (display-graphic-p).

There are a number of variables that affect the style of the displayed
clock. For now, I've chosen to be conservative and just expose
`doom-modeline-time-clock-minute-resolution' as a custom variable,
leaving the rest as constants. We may well want to revisit this in the
future.

I've personally been running this variant of the time segment for over a
year now, and as a result am pretty confident there are no behaviour or
performance issues with this implementation.

This implementation is originally sourced from
https://github.com/tecosaur/emacs-config/blob/a3c3b73a00f4e034ffeae11f20b00d1eb948a6e6/config.org#time.

README.md

@@ -237,6 +237,10 @@ Run `M-x customize-group RET doom-modeline RET` or set the variables.
 ;; It respects option `doom-modeline-icon' and option `doom-modeline-time-icon'.
 (setq doom-modeline-time-live-icon t)
 
+;; Whether to use an analogue clock svg as the live time icon.
+;; It respects options `doom-modeline-icon', `doom-modeline-time-icon', and `doom-modeline-time-live-icon'.
+(setq doom-modeline-time-analogue-clock t)
+
 ;; Whether to use unicode as a fallback (instead of ASCII) when not using icons.
 (setq doom-modeline-unicode-fallback nil)
 

doom-modeline-core.el

@@ -233,6 +233,20 @@ It respects option `doom-modeline-icon' and option `doom-modeline-time-icon'."
   :type 'boolean
   :group 'doom-modeline)
 
+(defcustom doom-modeline-time-analogue-clock t
+  "Whether to draw an analogue clock SVG as the live time icon.
+
+It respects options `doom-modeline-icon', `doom-modeline-time-icon', and
+`doom-modeline-time-live-icon'."
+  :type 'boolean
+  :group 'doom-modeline)
+
+(defcustom doom-modeline-time-clock-minute-resolution 1
+  "The clock will be updated every this many minutes, truncated.
+See `doom-modeline-time-analogue-clock'."
+  :type 'number
+  :group 'doom-modeline)
+
 (defcustom doom-modeline-unicode-fallback nil
   "Whether to use unicode as a fallback (instead of ASCII) when not using icons."
   :type 'boolean

doom-modeline-segments.el

@@ -3080,28 +3080,73 @@ mouse-3: Restart preview"
 ;; Display time
 ;;
 
+(defconst doom-modeline--clock-hour-hand-ratio 0.45
+  "Length of the hour hand as a proportion of the radius.")
+
+(defconst doom-modeline--clock-minute-hand-ratio 0.7
+  "Length of the minute hand as a proportion of the radius.")
+
+(defconst doom-modeline--clock-inverse-size 4.8
+  "The size of the clock, as an inverse proportion to the mode line height.")
+
+(defvar doom-modeline--clock-cache nil
+  "The last result of `doom-modeline--generate-clock'.")
+
+(defun doom-modeline--generate-clock ()
+  "Return a string containing the current time as an analogue clock svg.
+When the svg library is not availible, return nil."
+  (cdr
+   (or (and (equal (truncate (float-time)
+                             (* doom-modeline-time-clock-minute-resolution 60))
+                   doom-modeline--clock-cache))
+       (and (require 'svg nil t)
+            (setq doom-modeline--clock-cache
+                  (cons (truncate (float-time)
+                                  (* doom-modeline-time-clock-minute-resolution 60))
+                        (with-temp-buffer
+                          (svg-insert-image
+                           (micro-clock-svg
+                            (string-to-number (format-time-string "%-I")) ; hour
+                            (* (truncate (string-to-number (format-time-string "%-M"))
+                                         doom-modeline-time-clock-minute-resolution)
+                               doom-modeline-time-clock-minute-resolution) ; minute
+                            (/ doom-modeline-height doom-modeline--clock-inverse-size) ; radius
+                            "currentColor"))
+                          (propertize
+                           " "
+                           'display
+                           (append (get-text-property 0 'display (buffer-string))
+                                   '(:ascent center))
+                           'face 'doom-modeline-time
+                           'help-echo (lambda (_window _object _pos)
+                                        (format-time-string "%c"))))))))))
+
 (defun doom-modeline-time-icon ()
   "Displays the time icon."
-  (doom-modeline-icon
-   'mdicon
-   (if doom-modeline-time-live-icon
-       (pcase (% (caddr (decode-time)) 12)
-         (0 "nf-md-clock_time_twelve_outline")
-         (1 "nf-md-clock_time_one_outline")
-         (2 "nf-md-clock_time_two_outline")
-         (3 "nf-md-clock_time_three_outline")
-         (4 "nf-md-clock_time_four_outline")
-         (5 "nf-md-clock_time_five_outline")
-         (6 "nf-md-clock_time_six_outline")
-         (7 "nf-md-clock_time_seven_outline")
-         (8 "nf-md-clock_time_eight_outline")
-         (9 "nf-md-clock_time_nine_outline")
-         (10 "nf-md-clock_time_ten_outline")
-         (11 "nf-md-clock_time_eleven_outline"))
-     "nf-md-clock_outline")
-   "⏰"
-   ""
-   :face '(:inherit doom-modeline-time :weight normal)))
+  (or (and doom-modeline-time-live-icon
+           doom-modeline-time-analogue-clock
+           (display-graphic-p)
+           (doom-modeline--generate-clock))
+      (doom-modeline-icon
+       'mdicon
+       (if doom-modeline-time-live-icon
+           (pcase (% (caddr (decode-time)) 12)
+             (0 "nf-md-clock_time_twelve_outline")
+             (1 "nf-md-clock_time_one_outline")
+             (2 "nf-md-clock_time_two_outline")
+             (3 "nf-md-clock_time_three_outline")
+             (4 "nf-md-clock_time_four_outline")
+             (5 "nf-md-clock_time_five_outline")
+             (6 "nf-md-clock_time_six_outline")
+             (7 "nf-md-clock_time_seven_outline")
+             (8 "nf-md-clock_time_eight_outline")
+             (9 "nf-md-clock_time_nine_outline")
+             (10 "nf-md-clock_time_ten_outline")
+             (11 "nf-md-clock_time_eleven_outline"))
+         "nf-md-clock_outline")
+       "⏰"
+       ""
+       :face '(:inherit doom-modeline-time :weight normal))))
 
 (doom-modeline-def-segment time
   (when (and doom-modeline-time