Add support for background transparency toggling.

Since Emacs 29, frame background transparency is supported. Default keybindings
for background transparency toggling and transient state are added near
transparency toggling with key bindings bound to the keys `SPC T B`.

CHANGELOG.develop

@@ -75,6 +75,7 @@ the [[file:CHANGELOG.org][CHANGELOG.org]] file.
   (thanks to Sylvain Benner, Compro Prasad and Keith Simmons)
 - Added support for native fill column indicator in Emacs 27+ (thanks to
   Andriy Kmit)
+- Add support for background transparency aka true transparency. Key bindings are under ~SPC T B~ (thanks to JoshTRN)
 *** Breaking Changes
 **** Major
 - Support for Emacs 25 or Emacs 26 has been dropped, the minimal Emacs version

core/core-dotspacemacs.el

@@ -497,6 +497,13 @@ can be toggled through `toggle-transparency'."
   'integer
   'spacemacs-dotspacemacs-init)
 
+(spacemacs|defc dotspacemacs-background-transparency 90
+  "A value from the range (0..100), in increasing opacity, which describes the
+transparency level of a frame background when it's active or selected. Transparency
+can be toggled through `toggle-background-transparency'."
+  'integer
+  'spacemacs-dotspacemacs-init)
+
 (spacemacs|defc dotspacemacs-show-transient-state-title t
   "If non nil show the titles of transient states."
   'boolean

core/templates/.spacemacs.template

@@ -377,6 +377,11 @@ It should only modify the values of Spacemacs settings."
    ;; Transparency can be toggled through `toggle-transparency'. (default 90)
    dotspacemacs-inactive-transparency 90
 
+   ;; A value from the range (0..100), in increasing opacity, which describes the
+   ;; transparency level of a frame background when it's active or selected. Transparency
+   ;; can be toggled through `toggle-background-transparency'. (default 90)
+   dotspacemacs-background-transparency 90
+
    ;; If non-nil show the titles of transient states. (default t)
    dotspacemacs-show-transient-state-title t
 

doc/DOCUMENTATION.org

@@ -93,6 +93,7 @@
     - [[#title][Title]]
       - [[#iconified-tabified-title][Iconified (tabified) title]]
     - [[#transparency][Transparency]]
+    - [[#background-transparency][Background transparency]]
 - [[#layouts-and-workspaces][Layouts and workspaces]]
   - [[#layouts][Layouts]]
     - [[#the-default-layout][The default layout]]
@@ -1669,6 +1670,20 @@ In the transient state:
 | ~T~           | toggle transparency on and off |
 | ~q~           | quit transient state           |
 
+*** Background transparency
+The Frame background transparency can be toggled with: ~SPC T B~
+
+This also opens the Frame Background Transparency Transient State.
+
+In the transient state:
+
+| Key binding   | Description                               |
+|---------------+-------------------------------------------|
+| ~+~, ~=~, ~k~ | increase background transparency          |
+| ~-~, ~_~, ~j~ | decrease background transparency          |
+| ~T~           | toggle background transparency on and off |
+| ~q~           | quit transient state                      |
+
 * Layouts and workspaces
 Layouts are window configurations with buffer isolation. Each layout can define
 several workspaces (think of them as sub-layouts), sharing the same list of

layers/+spacemacs/spacemacs-defaults/keybindings.el

@@ -1053,3 +1053,69 @@ If FRAME is nil, it defaults to the selected frame."
   'spacemacs/scale-transparency-transient-state/spacemacs/toggle-transparency)
 
 ;; end of Transparency Transient State
+
+;; Background Transparency transient-state
+
+(defun spacemacs/enable-background-transparency (&optional frame alpha-background)
+  "Enable background transparency for FRAME.
+If FRAME is nil, it defaults to the selected frame.
+ALPHA is a pair of active and inactive transparency values. The
+default value for ALPHA is based on `dotspacemacs-background-transparency'"
+  (interactive)
+  (message (number-to-string dotspacemacs-background-transparency))
+  (let ((alpha-setting (or alpha-background dotspacemacs-background-transparency)))
+    (message (number-to-string alpha-setting))
+    (set-frame-parameter frame 'alpha-background alpha-setting)))
+
+(defun spacemacs/disable-background-transparency (&optional frame)
+  "Disable background transparency for FRAME.
+If FRAME is nil, it defaults to the selected frame."
+  (interactive)
+  (set-frame-parameter frame 'alpha-background 100))
+
+
+(defun spacemacs/toggle-background-transparency (&optional frame)
+  "Toggle between transparent and opaque background state for FRAME.
+If FRAME is nil, it defaults to the selected frame."
+  (interactive)
+  (let ((alpha-background (frame-parameter frame 'alpha-background))
+        (dotfile-setting dotspacemacs-background-transparency))
+    (if (equal alpha-background dotfile-setting)
+        (spacemacs/disable-background-transparency frame)
+      (spacemacs/enable-background-transparency frame dotfile-setting))))
+
+(defun spacemacs/increase-background-transparency (&optional frame)
+  "Increase background transparency for FRAME.
+If FRAME is nil, it defaults to the selected frame."
+  (interactive)
+  (let* ((current-alpha (or (frame-parameter frame 'alpha-background) 100))
+         (message current-alpha)
+         (increased-alpha (- current-alpha 5)))
+    (when (>= increased-alpha frame-alpha-lower-limit)
+      (set-frame-parameter frame 'alpha-background increased-alpha))))
+
+(defun spacemacs/decrease-background-transparency (&optional frame)
+  "Decrease backrgound transparency for FRAME.
+If FRAME is nil, it defaults to the selected frame."
+  (interactive)
+  (let* ((current-alpha (or (frame-parameter frame 'alpha-background) 100))
+         (decreased-alpha (+ current-alpha 5)))
+    (when (<= decreased-alpha 100)
+      (set-frame-parameter frame 'alpha-background decreased-alpha))))
+
+(spacemacs|define-transient-state scale-background-transparency
+  :title "Frame Background Transparency Transient State"
+  :doc "\n[_+_/_=_/_k_] increase transparency [_-_/___/_j_] decrease [_T_] toggle [_q_] quit"
+  :bindings
+  ("+" spacemacs/increase-background-transparency)
+  ("=" spacemacs/increase-background-transparency)
+  ("k" spacemacs/increase-background-transparency)
+  ("-" spacemacs/decrease-background-transparency)
+  ("_" spacemacs/decrease-background-transparency)
+  ("j" spacemacs/decrease-background-transparency)
+  ("T" spacemacs/toggle-background-transparency)
+  ("q" nil :exit t))
+
+(spacemacs/set-leader-keys "TB"
+  'spacemacs/scale-background-transparency-transient-state/spacemacs/toggle-background-transparency)
+