focused()
A Boolean variable that's true if the window is focused and false if not.
Note: The window can only receive input if it's focused.
Examples

-- Open this example in two separate browser
-- windows placed side-by-side to demonstrate.
function setup()
size(100, 100)
describe('A square changes color from green to red when the window is out of focus.')
end
function draw()
-- Change the background color
-- when the window
-- goes in/out of focus.
if focused then
background(0, 255, 0)
else
background(255, 0, 0)
end
end