bug#51309: 28.0.60; [Feature Request] Allow to customize tab-bar button images

[Carlos Pita <carlosjosepita2@gmail.com>]

Hi Juri,

> This definitely should be customizable, but it's unclear what do you
> want to customize: only the file path to the image, or allow to set
> the button propertized with an image with image properties like
> :margin/:ascent?

Probably the entire (image ...) descriptor. So it's possible to use svg
images (with rsvg enabled which now is the
default) that will work fine at any resolution. Also, even if the images
are correctly centered, they look vertically misaligned wrt text, this
is pretty common and tweaking the ascent may help, I guess.

And perhaps setting a nil descriptor should be allowed as a way to
disable the image altogether.

> Could you send such a button string with an image that looks good
> on HiDPI screens?  Then we could try to make a customizable option
> based on your design.

Vectorized images will do it. Otherwise you will have to provide pixmaps
at twice the resolution and, anyway, with fractional scaling they might
end up being blurry again (although not so much as when scaling up
x2). I assume there are not many devices with higher scaling factors
running emacs out there, yet...

There are plenty of free svg icons for light and dark themes here:
https://github.com/microsoft/vscode-icons/tree/main/icons.

Best regards,
Carlos