Add support for rounding specific corners

[yshui]

Discussed in https://github.com/yshui/picom/discussions/918

^{Originally posted by snoweuph November 9, 2022} I currently am ricing my i3 with picom and i've got the big problem that in the Tabbed mode the Tabbed bar is seen as an extra Window and so is completely separately rounded from the windows inside of it

I currently can Only Exclude the i3 tabbed bar from getting rounded and only.

# Exclude conditions for rounded corners.
rounded-corners-exclude = [
  "class_g = 'i3-frame'",
];

overall like this ending like this I can't only select windows who are in a tabbed i3 environment, because there's nothing specificly differentiating them from normal windows when I look them up with xprop

so my request put short is:

• let me only exclude specific corners for specific windows, so I can make that bar rounded on the top and not rounded on the bottom
• some way to use new setting on the i3 tabbed container maybe there is one already and i'm just to stupid

Suggestion

The option could look like this

rounded-corners-exclude = [
  "window_type = 'unknown'",
  "class_g = 'i3-frame'" 0 0 1 1,
]

the extra 4 numbers after the selector are for the corners in clockwise order starting from top left, 0 meaning don't select these for the excluding, 1 meaning this should get excluded, so that this would end up with rounded corners on the top but none one the bottom

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Also supersedes #1442