Displacement Slowness Again,

[RE:FORM_STUDIOS]

I am trying to render a large format image at 3000+ wide. I am finding major slowdowns when using 2d displacements that make displacement pretty much unuseable. The strange thing is that it slows down the GI calculation on areas that are not displaced. It also reduces my cpu load to sub-50%. Switching off displacement in the global switches fixes the problem.

I've looked through the forum for solutions to the problem but couldn't find anything that has fixed it.

Could anyone list the suggested parameters to change to solve the problem? Is it a sampling issue? or do I need to change the GI settings for the displaced objects?

Is this a bug or something to deal with through optimising my scene? Will Vray 1.5 speed fix this slowdown?

Loving the results, but not happy at hitting a brick wall when trying to render at high res with displacement(2d) switched on.

[dlparisi]

Are you getting any errors in the V-Ray log window?

[RE:FORM_STUDIOS]

Only :-

warning: Scene bounding box is too large, possible raycast errors.

[Morbid Angel]

well, the error you are getting could be partially responsible. Try eather to scale the scene down or change 2d displacement to 3d displacement.

[RE:FORM_STUDIOS]

Thanks for the quick feeback guys!

Well the 3d mapping seems to make the problem worse.

My units settings are as follows:

Display Unit Scale : Meters
Lighting Units : International

System Unit Setup -

System Unit Scale : 1 unit = 1 Meter
Respect System Units in Files is checked
Origin 16777215.0m
Distance from Origin 1m
Resulting accuracy 0.0000001192m

I am loath to scale things.

If I scale the model down x .001, can I change the units to mm and not expect any problems with my mapping? (guess I'll try it and see )

[Morbid Angel]

well your system scale does not match mine even a closest bit, I would suggest mesuring your scene, i.e. how long is it, how does it match to the real world, i.e. a house cannot be a kilomiter high etc. You should be able to scale down the scene with minor problems:
1 - if you have any procedural textures, they will be affected
2 - displacement strenth will also be affected

having respect scale in files checked would mean that if you import an object which is 1 m high and in that scene the mesurement is in metric, and you import it to a scene where mesurement is kilometers, respectfully the 1 m object will remain 1 m, but if you uncheck it will come in as 1 kilometer.

[RE:FORM_STUDIOS]

Interesting.
I scaled the scene down by a factor of 0.001 and vray is now throwing up alot of errors.

"Warning: Invalid surface normal (xxx, xxx, xxx) for "xxxx", using geometric normal. "

[Morbid Angel]

this means that your displacement is in conflict with the surface, or surface has a bad topology, what are you displacing?
I had the same problem.

[RE:FORM_STUDIOS]

The problem was that I had used displacement in the material of one of my objects. With 'overide max displacement' selected in the vray render properties checked, it must have been using 3d displacement. Switching off the displacement in the material fixed the problem.

From what you say, I need to suss out efficient settings for using 3d displacement. For the time being 2d displacement seems to be meeting my needs.

[RE:FORM_STUDIOS]

Weirdness continues!

I switched off all displacement in the scene manually, and the render would still only hit 50% cpu load. Switching off displacement in the render settings resolved the problem even though there wasnt anything being displaced!... Confused, I thought I would see if removing the displaced objects from the scene would fix things.... so I removed a wall that had a subdivide modifier on.... and the cpu load on render went back up to 100%. Curious, I tried deleting the subdivide modifier from the stack, and lo and behold, render load was back to 100%. So, it seems there might be a conflict between the subdivide modifier and vray.

I will investigate further!

[RE:FORM_STUDIOS]

Not sure what the issue with subdivide was, but I found an object with 3d displacement mapping that was also causing vray to trip out. Having the subdivisions above 128 caused cpu loading to drop to 50%. From my understanding of the manual, this value is rounded up to the nearest factor of 2, ie 256? Keeping the subdivs to 128 or below keeps the cpu running at 100%, but means my displaced grass is visibly tesselated. I think I need to tesselate the mesh prior to the displacement mod to get the desired result.

[panthon]

I ran into similar problems. I have a entire thread talking about it and i got no feasible explanation for the problem... I ended changing vraydisplacement mods into MAX standard displace modifier and the problem was solved. I´ve encountered 50% slowdowns several times and Vlado told me to turn Bitmap pager off, and it worked! Try it!

[RE:FORM_STUDIOS]

Bitmap pager? do you mean the 'reload textures on change' option on the files preferences page?

Well, thanks to Morbid, I worked out that the problem I had stemmed from using bad topology on the shape I had displaced.

I had created the grass plane using a spline with curves with a poly modifier applied resulting in a poor topology and loads of stretched polys. After shapemerging the outline of the grass area with a highly subdivided plane, I was able to remove all the rogue vertices left over in the shapemerge, and make sure all polys were quads. This meant I could reduce the displacement subidivisions to a level that eradicated the cpu slowdown without loosing detail in the displacement.

Lesson learnt, dont take shortcuts on meshes that will be vray displaced!