Feat (or bug?) - Change new background-opacity-cells to behave like Alacritty

[PowerUser64]

I've been testing out the newly-added background-opacity-cells option that was added as requested in #5911. The option is supposed to make the background of all transparent so the whole terminal can be transparent, which (according to the initial feature request) mimics how Alacritty does transparency with its transparent_background_colors option. However, in its current state, I don't think the background-opacity-cells option will satisfy most users who want to mimic what Alacritty does.

Here's a screenshot of the feature, as it appears in Ghostty (left), and Alacritty (right):

Notice how the window in the upper left is less transparent than the others

On the top, I have Neovim running in both Ghostty and Alacritty, which is an application that paints the whole screen with a background color. Ghostty is set to use the background-opacity-cells option, which should make the cell backgrounds transparent (like Alacritty), but it doesn't.

The problem is how transparency is applied in rendering. The current solution results in the opacity of cells stacking with the normal opacity of the terminal, so the cells with a background color end up being considerably more opaque than those without a background color.

Alacritty, on the other hand, uses the transparent_background_colors option to apply the opacity at a later stage in its rendering pipeline. Rather than applying it in a way that causes the terminal's "normal" background opacity to blend with the text layer's opacity, it applies it such that the opacity of the terminal overwrites the opacity of the cells.

I suggest that Ghostty change how its background-opacity-cells works to match Alacritty's behavior, because I believe that it is more desirable in most cases. The current behavior could even be considered bugged if going by what's said in the original feature request.

Thoughts?

[rhodes-b]

i only took a very quick glance at this but i assume its a duplicate of this
#7957

[PowerUser64]

Yeah it is, thanks. I'll add to that one.