Tentatively adapt to Modus 4

FTR, things that I expect to need further tweaks and/or discussions
with Prot:

(a) no "version" command, so it's kind of hard to guess what we are
    working with programmatically,

(b) preset palettes overrides are unavailable before loading the
    themes, and we can't require 'modus-themes either; maybe the
    manual should point out that users who want to use those presets
    should (1) do that in :config (2) load the theme twice?

(c) lots of backgrounds look very light/saturated to me even in the
    "faint preset": e.g. diff backgrounds, selected completion,
    region, eldoc current argument.

1 files changed, 54 insertions, 4 deletions

diff --git a/.emacs b/.emacs
index b810d3c..d9b99ab 100644
--- a/.emacs
+++ b/.emacs
@@ -640,9 +640,7 @@
   :custom
   (use-package-always-defer t))
 
-(use-package emacs
-  :when (>= emacs-major-version 28)
-  :init
+(defun my/modus<4-config ()
   (setq modus-themes-bold-constructs t
         modus-themes-deuteranopia t
         modus-themes-diffs 'bg-only
@@ -657,9 +655,61 @@
         modus-themes-prompts '(background)
         modus-themes-region '(bg-only)
         modus-themes-variable-pitch-ui t)
-  :config
   (load-theme 'modus-vivendi))
 
+(defun my/hsl-to-rgbhex (h s l)
+  (apply
+   'color-rgb-to-hex
+   `(,@(color-hsl-to-rgb h s l) 2)))
+
+(defun my/decline-diff-hue (h)
+  (list-colors-display
+   (seq-map (lambda (l) (my/hsl-to-rgbhex h 1.0 l))
+            '(0.04 0.08 0.16))))
+
+(defun my/modus>=4-config ()
+  (setq modus-themes-bold-constructs t
+        modus-themes-italic-constructs t
+        modus-themes-mixed-fonts t
+        modus-themes-variable-pitch-ui t
+        modus-themes-headings '((1 . (variable-pitch 1.2))
+                                (2 . (variable-pitch 1.15))
+                                (3 . (variable-pitch 1.1))
+                                (4 . (variable-pitch 1.05))
+                                (t . (variable-pitch)))
+        modus-themes-org-blocks 'gray-background)
+  (load-theme 'modus-vivendi-deuteranopia)
+  (setq modus-vivendi-deuteranopia-palette-overrides
+        ;; TODO: set bg-prompt?
+        `(;; (my/decline-diff-hue 0.14)
+          (bg-removed-faint     "#141100")
+          (bg-removed           "#282200")
+          (bg-removed-refine    "#514400")
+          ;; (my/decline-diff-hue 0.59)
+          (bg-added-faint       "#000914")
+          (bg-added             "#001228")
+          (bg-added-refine      "#002551")
+          ;; (my/decline-diff-hue 0.76)
+          (bg-changed-faint     "#0b0014")
+          (bg-changed           "#160028")
+          (bg-changed-refine    "#2d0051")
+          ,@modus-themes-preset-overrides-faint))
+  (load-theme 'modus-vivendi-deuteranopia))
+
+(use-package emacs
+  :when (>= emacs-major-version 28)
+  ;; `(modus-themes) Sample configuration with and without
+  ;; use-package' recommends setting options in :init and loading the
+  ;; theme in :config; unfortunately it's not possible to access the
+  ;; palettes without loading the themes AFAICT, so do everything in
+  ;; :config.
+  :config
+  (cond
+   ((memq 'modus-vivendi-deuteranopia (custom-available-themes))
+    (my/modus>=4-config))
+   (t
+    (my/modus<4-config))))
+
 (use-package package
   :custom
   (package-selected-packages