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.
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