Got some old loops of cracked/brittle garden hose?
Hang it on a hook mounted high on the end wall of your garage ,about the middle of the garage is good.
About 20 ft will do ,loop it over the hook twice.
You now have 3-4bits of hose hanging down 5-8 feet.
will hang 3-5 in out from the wall.
Drive your car in,once you see the hose begin to move,you know your almost at the wall.
Then you can stop, or even edge in another inch or 2,the hose will prevent any damage.
If you do store stuff at the end wall or have presses etc,hang the hose from a rafter/similar so it hangs a couple of inches in front of these items.
I have tried string with a small plastic weight on the end ,to hit the windscreen at point x.,but its a lil hit and miss(groan) and there is no built in shock absorbtion.