vray gpu next and displacement.

[super gnu]

following on from my questions regarding the "affect channels" option in vray next gpu,

another concern i have is regarding displacement.

i understand it has been rewritten for NEXT.

does this mean it works with more complex stuff and heavier displacement than 3.6?

if so, another reason to consider the upgrade. quite urgently!



my current scene i just tried to add a bit of displacement to a set of shuttered concrete beams.

at lower resolutions and default edge length it works.

however my final render is 10k wide.

trying to render at that res, even with an edge length of 15 pixels (useless) maxes out my 64GB cpu ram, then errors out gpu with either out-of-memory or unhandled exception. in the second case i need to reload max/reboot before i can render again.

its hardly a demanding example of displacement.. just a bit of bumpiness to a row of 5-6 ceiling beams.

the same setting on cpu renders without hesitation, and using a fraction of the ram.

[vlado]

If you can attach some example scene, I will be able to run it and tell you the results. I've been able to render 10k wide images with displacement and it didn't seem to take exorbitant amounts of RAM (CPU or GPU).

Best regards,
Vlado

[super gnu]

hi Vlado, thanks for the reply, ive emailed you a test scene to vlado@ chaosgroup. if you can render that on a 12GB gpu and without using all of 64 gb ram, ill be very happy.

on a related note, does it still help subdividing the mesh before using displacement on gpu? i assume not since mesh is pre-tesselated.

[super gnu]

well i discovered that subdividing the mesh does indeed help massively with ram usage and general functionality. however im getting very strange results.

on gpu, if the edge length is larger than the triangles in the source mesh it makes a right mess.

it also seems to be ineffective with "keep continuity"

switching to rt cpu and the displacement looks as it should.

you can test this your self with the file i sent.

i put a subdivide on the mesh at around 0.05m.

set displacement edge length to say 10.

horrible mess, and split edges all over. no amount of tweaking of the edge threshold changes it.

switch to rt cpu and the displacement looks nice and the split edges are almost nonexistant.

reducing the edge length on gpu to say 6, makes displacement look better, but not great, and its still got splits all along the edges.

[super gnu]

ok its not related to edge length being bigger than triangles. even with a subdivide set ot 0.5m it still screws up.

[super gnu]

ok so i finally resolved all issues, and answered my own question!

ive moved onto the vray next demo, and displacement works much better. i still cant crank it up as high as id like, but i can get a decent result given im limited to 12GB on the gpu.

one observation is using "use object mtl" on gpu doesnt work properly with multiple materials in a blendmtl. the displacement takes the map only from the first material. switching to cpu and it renders as expected.

i got around this by using the blending map in a mix map on the displacement mod. , with the two displacement maps inside that.