This is possibly hard water deposits (limescale), which can be removed with vinegar. Check you are using the correct dosing of detergent.
Important
In the interest of consumer safety, any adjustments, alterations or replacement
parts should only be made or fitted by a suitably qualified and competent person
with the machine disconnected from the mains supply.
Check that rinse aid and salt are topped up if you are using these separately. If you are using a 3 in 1 or similar tablet formulation, find out if your water supply is particularly hard or not. If it is hard then extra salt may need to be added to boost the water softening effectiveness, or alternatively you might find it more cost effective to use separate detergent, rinse aid and salt.
Important
In the interest of consumer safety, any adjustments, alterations or replacement
parts should only be made or fitted by a suitably qualified and competent person
with the machine disconnected from the mains supply.
If the film can not be removed with vinegar then the glass is probably pitted due to irreversible damage. Make sure that the glasses are dishwasher proof. Use a low temperature wash programs and make sure your glassware is dishwasher safe.
Important
In the interest of consumer safety, any adjustments, alterations or replacement
parts should only be made or fitted by a suitably qualified and competent person
with the machine disconnected from the mains supply.