switcher.ui.highlight rounded corners? about hammerspoon HOT 2 CLOSED

It's possible, but requires messing with hs.window.switcher's internals even more using Lua's debug functions:

local function findUpvalue(f, name)
	local i = 0
	local n, v
	repeat
		i = i + 1
		n, v = debug.getupvalue(f, i)
	until not n or n == name
	if not n then return nil end
	return i, v
end

local setUiPrefsUpvalueIndex, oldSetUiPrefs = findUpvalue(hs.window.switcher.new, 'setUiPrefs')
if not setUiPrefsUpvalueIndex then
	error "Couldn't find hs.window.switcher's setUiPrefs function"
end
debug.setupvalue(hs.window.switcher.new, setUiPrefsUpvalueIndex, function(self)
	oldSetUiPrefs(self)
	local highlightRadius = self.ui.highlightRadius or 0
	self.drawings.highlightRect:setRoundedRectRadii(highlightRadius, highlightRadius)
end)

-- Now you can do:
hs.window.switcher.ui.highlightRadius = 10 -- or whatever
ws = hs.window.switcher.new( --[[ whatever arguments ]] )

-- or for a specific switcher:
ws.ui.highlightRadius = 15 -- or whatever

There are three radii that are computed and used by hs.window.switcher, so it depends which one you're trying to match:

• ui.titleRectRadius: Used for the window titles in the main switcher area. Defined as 1/4 of ui.textSize (which defaults to 16, making this radius 4).
• selectedRectRadius: Used for the large preview box for the selected window, as well as the title box at the top of that preview. Defined as 1/4 of the height of an uppercase O in the selected-window title font (with the odd effect of not rounding those corners if you turn that title off). With default settings, that seems to work out to 8.
• padding: Used for the corners of the switcher itself. Also has some non-corner-radius uses: It's the amount of space between two thumbnails, or between the first/last thumbnail and the corresponding edge of the switcher. Defined in a complicated way based on ui.thumbnailSize, the number of windows, and the available screen width. If you're trying to match the switcher's corners, it will probably take a more involved patch to actually find that value.