Emacs 29.1 Transparency Alpha On Sway

I have just been been going through the new features added to emacs 29.1 and have been trying out the transparency or alpha-background on sway.

“alpha-background controls the opacity of the text background when running on a composited display.”.

I was keenly looking for an emacs improvement to the swaywm built in compositing method which in the case of emacs would make transparent the whole window including text which of course isn’t ideal.

I had defined the following in my sway config file:

for_window [class="Emacs"] opacity 0.92

0.92 seemed to be the perfect balance between wallpaper visibility and text legibility.

I am now going to compare the emacs alpha-background method with an equivalent sway emacs compositing opacity.

So for emacs I am going to set something like:

(set-frame-parameter nil 'alpha-background 70)
(add-to-list 'default-frame-alist '(alpha-background . 70))

See the following images for a comparison (can you guess which is which?) - I would suggest opening each image in separate browser tabs and comparing that way.

Note/Disclaimer: I chose opacity values that displayed an equivalent wallpaper visibility through emacs and as it turned out the opacity values were different which I suspect relates to the way the sway compositor is processing its opacity value rather than the way emacs does it but the demonstration fundamentally should still be a valid one.

and here is a more detailed comparison on a selected screen region:

Suffice it to say that this is a very nice improvement and certainly something I shall be using from now on.