This is an older, easier to implement variant of CAS as a pure
fragment shader. It doesn't support upscaling, but we won't make
use of it (at least for now).
The sharpening intensity can be adjusted on a per-Viewport basis.
For the root viewport, it can be adjusted in the Project Settings.
Since `textureLodOffset()` isn't available in GLES2, there is no
way to support contrast-adaptive sharpening in GLES2.
It can be enabled in the Project Settings
(`rendering/quality/filters/use_debanding`). It's disabled
by default as it has a small performance impact and can make
PNG screenshots much larger (due to how dithering works).
As a result, it should be enabled only when banding is noticeable enough.
Since debanding requires a HDR viewport to work, it's only supported
in the GLES3 backend.
Changed the behaviour of the Linear tonemapping operator to not clamp to [0, 1] range
in the case when KEEP_3D_LINEAR is defined. This allows to render values > 1.0 in
floating point texture targets (via Viewport) for further processing or saving high
dynamic range data into files. This only works when no color conversion is active.
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.
