vray distance texture bug

[Bigguns]

Hi, the vray distance texture, when used on small object vs big object, like in the scene provided take's ages to render, it's crazy slow. Before it was super fast. something is broken now.

Let me know
thank you

[yavor.rubenov]

Hello,

I'm trying to reproduce this issue but no luck so far. If i just open and render the attached scene - it's ready in 12 seconds and I get similar render time with V-Ray 3.7.

What render times are you seeing ?

Best regards,
Yavor

[Bigguns]

try with this scene and render in close up

[yavor.rubenov]

With this scene I got the slow down too.
I tried it with older versions (3.7) but it is also slow there. In what V-Ray version was this scenario fast for you ?

Overall in the scene you have 2 objects with displacement with very low edge length - both are set to 3.0. Both displacements have the "Static geometry" option turned off which makes rendering slower. Additionally you are rendering an orthographic viewport - with it "View Dependent" is better to be off.

I tried to set both displacements to generate static geometry but 32 GB RAM were simply not enough - at more than 120 000 000 triangles generated it was at about 10% of the geometry.

[Bigguns]

that particular scene I created it to show you the problem. So I never tried it in an older vray version. But, if you render the same thing using a smaller object, it render just fine. the bigger the object, the slower it get's, there is a problem when using distance texture and displacement. the image I joined show's you that if the plane ( or surface ) is small vs what the vray distance text is used, like in this exemple I have object interpenetraing all over the surface, it render SUPER fast and take's low ram, if I increase the size of the plane, the more I scale it, the slower it gets and it get's to the point where it don't render and I have to kill max. It's not normal ! something is going on

[yavor.rubenov]

When you increase the size of the plane it is expected that displacement gets slower and I'll try to explain why.

Take for example a plane with size 1x1m. I've added a turbo smooth modifier so that it is similar to the scene you've sent. Here I used edges tex to show the triangles:

In this case we get 32 triangles.
Next - the same plane but this time its size is 10x10m:

Notice that the number of triangles remains the same - 32. It's just their area that changes.

Now the original 1x1m plane with view dependent subdivision displacement with edge length 3. I use a simple texture with a white circle here (will get to the distance tex a bit later):

Now the triangles are 2048 - the whole plane is subdivided so that each subtriangle has an edge up to 3 pixels length.

Here I've changed the size of the plane to be 10x10 m. Everything else remains the same.


Notice how the triangles are now 131072 - that's 64 times more triangles that we had to generate. This happens because the original triangles are now much bigger and we have to subdivide them more to get to the required edge length of 3 pixels.
The only difference that happens when you use distance texture is that it is actually slower to calculate and we need to evaluate it many many times to generate those 131072 faces. If anything changed lately to the distance texture - it is actually much faster to calculate in V-Ray Next compared to V-Ray 3 (but still it is a complex to calculate texture).

One last thing - when you say you increase the size of the plane - do you mean you increase the Length/Width or you scale it ? While doing the tests I noticed that for some reason if I scale the plane to some size I get more triangles than when I change Length/Width to the same size. We'll check why this happens.

[Bigguns]

yeah there is something wrong going for sure. I understand that the displacement would take more time to calculate if the object is bigger, but without the vray distance texture all my project render's perfectly and close up or not. When I add the dist txt it freeze.. there is something wrong there. and it look's like there is inconsistency because I was able to do it in the past ( older project, maybe 2 or 3 years ago ) and a freidna of mine just did it for his face, I told him how I was doing it in the past he did it and it worked for him, but no chance on my side.. that's odd. He has it on the face and it render just at the eyelash intersection with skin and it renders fast he told me. I will try the only thing I did not try , and it would be very odd if it work's but, I will blend it with the displacement map via the composite like it should be in the end ( I did not tried since it was not working on his own, but maybe blended in the displacement map it will .. who know's ). ----------------

Also, have you tried to do close up shot of the scene I sended you ? it freezes... but futher away it renders .. not normal to me.