This decreases the number of samples significantly, leading to a
notable performance increase with only a very slight loss in
visual quality.
This also tweaks the default SSAO settings to use 3×3 blurring,
which makes noise patterns much less visible.
As of clang-format 6.0.1, putting the `/* clang-format off */` hint
around our "invalid" `[vertex]` and `[shader]` statements isn't enough
to prevent a bogus indent of the next comments and first valid statement,
so we need to enclose that first valid statement in the unformatted chunk.
Rémi Verschelde
Hugo Locurcio
Juan Linietsky
Gilles Roudiere