displacement bugs and optimizations

[Alessandro Padovani]

4.1.0.2162

There'a a small bug that subdivision is not generated if we only have the displacement subdivision in daz studio. Plus in this case we can use the simple subdivision instead of catmull, that's much faster since it doesn't have to smooth. Test scene subd-duf.

# subdivision
if there's mesh subd and displacement subd
    use catmull
else if there's only mesh subd
    use catmull
else if there's only displacement subd
    use simple

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In the daz displacement group we don't need to convert the texture to bw since the input is non-color already, also we can use a multiply add node.

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[Thomas Larsson]

Nice with a straightforward bug. Fixed in last commit.

[Alessandro Padovani]

Commit 80c029b works great, thank you for the fast fix.

note. displacement in global settings. It seems there’s a known limitation for “displacement and bump“, that can’t smooth and only renders flat polygons. This seems a limitation by design so not considered a bug by the blender team, as usual. The suggested workaround is to increase the subdivision, which seems ridiculous to me because this defeats the purpose of “displacement and bump“ entirely.

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https://projects.blender.org/blender/blender/issues/74367

Anyway, given this “limitation“ we may provide a global setting for displacement so the user can choose as desired.

• “displacement and bump“: fake details with a bump map if the subdivision is not enough, renders flat.
• “displacement only“: details are not visible if the subdivision is not enough, renders smooth.

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