Potential fix for clipping with parallel projection and transparent sky.

[ThatRedox]

Apply the parallel projection clipping fix to computeAlpha.
Fixes #1507 . Needs testing.

[leMaik]

I don't have the original scene that causes this bug. However, here is a scene that does clip in Chunky 2.3.0. It doesn't clip in 2.4.4 and it doesn't have this issue in 2.4.4.
clip.zip

[ThatRedox]

Thanks a lot! I was able to reproduce the clipping on 2.3.0 and was able to reproduce transparent sky clipping:
2.4.3 & master preview:

2.3.0

2.4.3

master

And the PR seems to fix this successfully:

Using camera 2:

{"camera":{"name":"camera 2","position":{"x":-300.778737752961,"y":-600.0,"z":-133.54153669576866},"orientation":{"roll":0.0,"pitch":-0.8237799582905735,"yaw":-0.7689488227289661},"projectionMode":"PARALLEL","fov":50.0,"dof":"Infinity","focalOffset":2.0,"shift":{"x":0.0,"y":0.0}},"cameraPresets":{"camera 1":{"name":"camera 1","position":{"x":-280.84383609719515,"y":-569.5120243228357,"z":-114.71654334937985},"orientation":{"roll":0.0,"pitch":-0.7853981633974483,"yaw":-0.7853981633974483},"projectionMode":"PARALLEL","fov":50.0,"dof":"Infinity","focalOffset":2.0,"shift":{"x":0.0,"y":0.0}}}}

[leMaik]

Glad you were finally able to reproduce this bug. I like the refactorings. :)