The waiting area gives good views of the apron and runway but the glass spoils it.
As with many Indian sub continent airports photography is prohibited (There are signs all over the place!!) as the airport is also used by the SL Airforce (who's hangers you can see beyond the runway as you view from the seating area).
Having said that , as long as you keep a low profile
and are quick (real quick) you could get away with it. An employee did come over shouting at me (he wasn't even security!!) a few years ago, but I managed to calm him down!!
You should be able to take photos from the Bus that takes you to the plane and back, as it does take you around the parked planes on the way.
If you can, be one of the last to disembark last as for some bizarre reason they always seem to send one bus short
and you get to wait around the aircraft till the next one arrives granting a good photo opportunity
People are often unreasonable, illogical and self- centered: Forgive them anyway - Mother Theresa