GNU bug report logs - #70697
30.0.50; Frame parameter alpha-background is ignored for fringe bitmaps & internal borders

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Package: emacs; Reported by: Aleksandar Dimitrov <mail@HIDDEN>; dated Wed, 1 May 2024 12:02:02 UTC; Maintainer for emacs is bug-gnu-emacs@HIDDEN.

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From: Aleksandar Dimitrov <mail@HIDDEN>
To: bug-gnu-emacs@HIDDEN
Subject: 30.0.50; Frame parameter alpha-background is ignored for fringe
 bitmaps & internal borders
User-Agent: mu4e 1.12.1; emacs 30.0.50
Date: Wed, 01 May 2024 12:52:58 +0200
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Hi all,

Runinng in any compositing window manager (this includes Wayland with a
PGTK build of Emacs, but also X without PGTK), the frame parameter
alpha-background is ignored for at least

- fringe bitmaps
- insets drawn with internal-border-width

The resulting visual effect is quite jarring, and makes both of these
difficult to use together with transparency.

Here's a small emacs -Q script to exhibit the problem:

#+begin_src emacs-lisp

;; Turn off scroll bars to make the bugs more visible.
(scroll-bar-mode -1)

;; set transparency & internal border width.
;; Note how the internal border is going to be drawn in a solid white colour
;; and will ignore the alpha value.
(modify-all-frames-parameters '((alpha-background . 50)
                                (internal-border-width . 20)))

(define-fringe-bitmap 'test-bitmap
  (vector (expt 2 15)) nil 16 '(top t))

;; Define a face for the fringe that has a different background colour, to
;; more easily discern the fringe bitmap bug from the internal border bug.
(make-face 'test-face)
(set-face-attribute 'test-face nil :background "pink")

;; Apply a fringe bitmap to all lines in the current buffer. Note how the fringe
;; bitmap is monochrome, but the background colour ignores the global alpha value.
(defun apply-fringe-bitmap ()
  "Apply a fringe bitmap to the current buffer to exhibit the transparency bug."
   (point-min) (point-max)
     #(" " 0 1 (display (left-fringe test-bitmap test-face)))
     #(" " 0 1 (display (left-fringe test-bitmap test-face))))))

(add-hook 'emacs-startup-hook #'apply-fringe-bitmap)


And here's how it looks like:
(that's my personal home page, not an image hoster.)

I would expect the white border around the frame to also be transparent,
and the fringe, too.


Acknowledgement sent to Aleksandar Dimitrov <mail@HIDDEN>:
New bug report received and forwarded. Copy sent to bug-gnu-emacs@HIDDEN. Full text available.
Report forwarded to bug-gnu-emacs@HIDDEN:
bug#70697; Package emacs. Full text available.
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Last modified: Wed, 1 May 2024 12:15:01 UTC

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