bump and caustics

[Jiri.Matys]

Hi,

bump on source (generate) object doesnt affect caustics. Is it a bug or? Seems really strange to me.

Thank you.

[Jiri.Matys]

Unfortunatelly displacement producing bad results in caustics. And bump mapping doesnt work.

standard mesh vs displacement

[Buck]

Have you tried increasing the max subdivisions displace? I don't know that this will fix it, but to me it looks like the mesh isn't subdivided enough in displacement.

Also, what are you using to displace, a bitmap, or procedural? If it's a bitmap, make sure it's at least 16 bit. (not 8 bit saved as 16, but actually created at 16 bit or higher)

[Jiri.Matys]

Its a bitmap. And with enough subdivision its better. But this displacement error is even in areas where displacement do nothing. And without displacement its smooth even with low subdivision. I have to subdivide it really lot to make it smooth with displacement.

[Buck]

sounds like that's the answer then, more subdivisions. You often need more subdivisions than you'd think, for displacement. I'd double check the bit depth on your map as well.

[Jiri.Matys]

Still its weird that it do this thing even where displacement is black and do nothing. When I disable displacement, caustics is ok with obsolutely same mesh.
And subdivison is not a good answer, because you really need to make it a LOT of subdivision to make it clear. But one screwdriver object in empty scene takes more then 30GB of RAM.

[^Lele^]

Still its weird that it do this thing even where displacement is black and do nothing. When I disable displacement, caustics is ok with obsolutely same mesh.

Black in displacement still subdivides the mesh.

And subdivison is not a good answer, because you really need to make it a LOT of subdivision to make it clear. But one screwdriver object in empty scene takes more then 30GB of RAM.

Indeed, you wouldn't want to go there unless needed.
Bump works just fine for me (see attached), maybe you could send support a scene to look at?

[Jiri.Matys]

Hmmm, that is weird, I will try that again. Only my bump was much much smaller, like real life small damages, but they still change caustics pretty well.

Now what I done in new test is subdivide mesh a lot for rendering and use displace modifier instead of displacrment. Ram is much better and caustics is affected.

[^Lele^]

Indeed, your second approach won't generate the same kind of topology (max's subdivide keeps quads as quads), so it may work well.
As for the bump, with Photon Mapping you're either going to have to use an insane amount of photons (hint: don't!), or raise the bump value a bit for the caustic pass (i.e. render twice: once for caustics, and once for the beauty, comp later.).

[Jiri.Matys]

Yes, you are right @^Lele^. So problem in displacement are triangulation. Do you think it can be corrected in some way?

You can see final result here:
https://forums.chaosgroup.com/forum/...caustics-study

[^Lele^]

Wow, very nice results, i love the amount of per-pixel detail and variation!
re:triangulation: i have seriously no idea.
What you could try is to use the other methods for subdivision of the mesh to displace, available in the modifier.
For example, using subdivision (with a displacement texture in the appropriate slot) with CK checked leads to very nice topology compared to the 3d mapping option (see attached).
You should however note that the 3d mapping technique is potentially a lot more efficient (it subdivides based on the map demands), so it should be used for stuff like terrains, water planes, and such.
The standard subdivision method, with or without "classic CK", is a lot more similar to how one would go about things with a standard max turbosmooth modifier, so a more regular triangles' topology is preferred to the efficiency of 3d mapping, but it saves you from subdividing the mesh in viewport, or before render starts, with one core.

[^Lele^]

Jiri.Matys , our displacement engineer would love to get a hold of your final scene (with the turbosmooth+max displacement) to see if he can make things better.
Send it to support, if you could, referencing this thread, or to me, and i'll pass it on directly.
No worries if it's a problem to share it with us, of course.

[Jiri.Matys]

There is no problem with turbosmooth and max displace modifier, caustics render fine with this setup. Or you mean make things better with vray displacement?