vray NEXT displacement wierdness

[super gnu]

testing out NEXT on a live job, and having some issues.

im trying to use GPU, having switched from 3.6 due to GPU displacement being a bit..err.. useless.

but im having problems with displacement here too.

ive got a roof beam, subdivided, properly mapped, with a mix map of 2 bitmaps driving 3d displacement. on an earlier gpu driver (380 something) i was able to bring the edge length down to around 7 pixels on a 10k wide render, and it rendered. on 6, it ran out of ram.

after updating driver to 417, i now cannot use an edge length lower than around 18 pixels without my gpu ram running out.

anyway, thats not the main issue.

on the rounded edges of the beams im getting some nasty thin glitches. its not a mapping issue.

here is a render:





so, just to check, i switched over to cpu NEXT and rendered a similar region..



the thin errors on the edge are gone..BUT, also.. what on earth is causing the difference in the render? its like the GPU displacement has 10x the detail. and possibly some glitches i assumed were in the texture. or its adding normal mapping on top of the displacement. whatever, CPU doesnt do it.

plus, that blurry CPU render was sitting on 48GB (!) of ram to render.. its basically an empty room, although there are 10 or so 8k textures in there.

help? neither of them are what id call "usable"

[GLASS-CANVAS]

In my experience putting a subdivide directly below the displacement in the stack will help massively with memory consumption and speed. If you run out of RAM, half the size of the subdivision. In most cases you'll want it fairly dense

[super gnu]

yes ive been using that trick forever.. and this mesh is quite finely subdivided. however im not sure these days, how that relates to gpu rendering (apart from the geometry prep at the beginning) since the whole displaced mesh is precomputed anyway.


my questions however are:


a) why is the gpu giving those nasty edge glitches

b) why is the cpu giving that low res result ( probably realistic given the low displacement detail setting)

and related to that, why is the gpu doing a much finer detailed job.. - i remeber reading ages ago that vray displacement adds fine detail using normal mapping automatically..

i assume that is what the gpu is doing.. in which case its broken on cpu.
- If it is doing normal mapping, it would be good to have a toggle for it so i can see what the displacement actually looks like..


and finally

c) why on earth is next cpu using 48gb of ram to do that crappy displacement on a few finely pre-subdivided concrete beams.

[GLASS-CANVAS]

Just out of interest, if you do a region render at edge length = 1 what does it look like? As you want it to? Or still not right?

[Nearl]

Check your texture filtering, maybe. CPU v GPU seems to handles assets differently so I wouldn't expect an exact match.