- Implement shadow fading when using the Orthogonal shadow mode
(like in `master`).
This allows customizing the distance at which directional shadows
start to fade away. Shadow fading will also always start at the same
distance now, regardless of the current shadow mode in use.
This is useful for enclosed levels to prevent shadows from fading
at all with a well-tuned maximum distance.
The default fade start value (0.8) results in fading happening later
in the distance compared to the previous behavior, where fading started
from the last shadow split distance (0.6 in PSSM 4 Splits and
0.1 in PSSM 2 Splits).
On some hardware, modifying gl_FragColor multiple times can cause large performance drops. This PR writes to a standard temporary variable instead, and copies across to gl_FragColor once only at the end of the fragment shader.
This could potentially lead to large gains in performance on affected hardware.
