Highlight macOS active windows using Hammerspoon init.lua

init.lua

local highlight = nil

local function highlightWindow()
    -- Clear any existing highlight
    if highlight then
        highlight:delete()
        highlight = nil
    end

    -- Get the currently focused window
    local win = hs.window.focusedWindow()
    if not win then
        return
    end

    -- Get the frame of the focused window
    local frame = win:frame()

    -- Create a new rectangle that slightly expands beyond the window's bounds
    local borderWidth = 5 -- Width of the border
    local highlightFrame = hs.geometry.rect(
        frame.x - borderWidth,
        frame.y - borderWidth,
        frame.w + (2 * borderWidth),
        frame.h + (2 * borderWidth)
    )

    -- Create the highlight rectangle
    highlight = hs.drawing.rectangle(highlightFrame)
    highlight:setStrokeColor({["red"] = 1, ["green"] = 0, ["blue"] = 0, ["alpha"] = 0.8})
    highlight:setStrokeWidth(borderWidth)
    highlight:setFill(false)
    highlight:setRoundedRectRadii(10, 10) -- Optional: rounded corners
    highlight:bringToFront(true) -- Ensure it's visible on top of the window
    highlight:show()
end

-- Bind the function to a hotkey (e.g., Ctrl + Alt + H)
-- hs.hotkey.bind({"ctrl", "alt"}, "H", highlightWindow)

-- Automatically remove the highlight when the focus changes
hs.window.filter.default:subscribe(hs.window.filter.windowFocused, function()
    highlightWindow()
end)

hs.window.filter.default:subscribe(hs.window.filter.windowUnfocused, function()
    if highlight then
        highlight:delete()
        highlight = nil
    end
end)