Until now, the zbuffer was written straight from the internal zbuffer,
which has values that are inverse-proportional (like 1.0/z) which makes
it very hard to use it for postprocess, like zblur or other composit effects
that require Z.
Based on info from ILM, the values stored for Z in exr files is the
actual distance from a camera. I think that's about time to migrate to that
convention!
By default now, after render, the z values are converted to floats. This
saves in exr files now, but not in the Iris Z files. That latter was a
blender-only anyway, so might be not a real hassle to drop. :)
You can see the difference in the image window, but notice the range now
is linear mapped from camera clipstart to clipend.
Note; I just discover that ortho Z values need a different correction...
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