Vray Clipper slows down render time dramatically

[RwVision]

Hi,

Ok, my current project is a treasure for finding out Vray issues...

Simple example, extraordinary result - same scene, setup, just one uses cray cliper with a mesh to clip unwanted geo.

Resulting in longer render time - although it should be even faster with clipper, when rendering less grass.
The problem does not limit to the clipping area but whole scene, that's a serious issue. It's like something invisible is calculating.

In my commercial scene, it's 3:30 vs ~5:30 and I only get rid of a small grass portion on the ground.

But I made a simple example and uploading the scene:
https://www.dropbox.com/sh/aqdgdjhif...Ab1Od-3Na?dl=0

1. Normal render - 35,4s Total



2. Using Vray clipper on small ground portion - 50,6s Total

[yavor.rubenov]

Hello,

V-Ray Clipper is a render time effect - this means that all the geometry (grass in your case) is still there. In addition to that every traced ray is checked against the clipper - while this is quite fast is still requires time..

Best regards,
Yavor

[RwVision]

Hey

What you're saying would be just plain unusuable. As I also mentioned, it affects whole image, not clipping area.

At least the render time should be the same, the longer render time is really big.

I remember 3.7 clipper worked like a charm.

[YunalZobu]

Hi RwVision ,

I took the liberty to play around with the scene a bit.
Steps 1 and 2 are the images I rendered out before doing any changes, so I have something to compare to. Step 1 is the time it took with the Clipper on.
Once I redistributed your grass patches I'm using the Plain effector with a box field to clamp the "cutting" of the grass to your custom mesh, that's on step 4.
And finally, step 3 is the render time I got with that setup, shaving around 10s of the render time I got without the Clipper (the faster one ).

Hope this will end up being useful for your final setup.

[RwVision]

Thanks Yunal

Is this something it could work with complicated mesh to.clip?

[YunalZobu]

I don't see any reason why it wouldn't work.
If you custom mesh is with quite small details, like very short and sharp edges, you might want to increase the resolution of the cloned patches, i.e. making the patches smaller and upping their count.
For the example above I used a patch with a size of 175x175cm.

[RwVision]

I don't see any reason why it wouldn't work.
If you custom mesh is with quite small details, like very short and sharp edges, you might want to increase the resolution of the cloned patches, i.e. making the patches smaller and upping their count.
For the example above I used a patch with a size of 175x175cm.

Could you send me your file? To be honest I don't know what you did If you just cloned smaller patches it is not a solution. Idea is to clip very large spaces with no restrictions - just like in 3.7

[YunalZobu]

To be honest I don't know what you did

nothing fancy really, just a simple mograph setup

If you just cloned smaller patches it is not a solution

well, as I mentioned, in order to have a more precise control I made a patch of 175 sq.cm and re-distibuted that.

Besides the bigger scene file size, I can't see a drawback.
Here is a link to the scene file - https://drive.google.com/file/d/1wtn...ew?usp=sharing
Let me know if it's helpful

[RwVision]

Well, as thought this is just an example, which works on the simple example - that's not the problem and final scene. Imagine large area with sidewalks, stones, anything curvy also, which you just clip by a clipper mesh just by the edges - never done it? Thanks for sharing though

yavor.rubenov - any response, did you check and investigate why rendering is slower, even in areas unaffected by clipper mesh? Any comparisons made to 3.7 clipper?

[yavor.rubenov]

There are no changes to the clipper itself for quite a while. As I mentioned - even areas that are not inside the clipper mesh still need to be checked so it is expected to have some slow down.
My colleagues from the Cinema team will check if there's something scene/Cinema specific.

[RwVision]

Thank for quick reply Yavor,

I understand perfectly, it will draw some render time but:

it is expected to have some slow down.

Exactly what you say is an issue - SOME slow down - where in my example it is (minus lC 10s) 25sec vs 40sec rendering - that's 60% more time. In a bigger scene you can just see it goes way slower to calculate.

[shaio]

Hey RwVision
Thanks for the scene. I'll check it alongside the dev team and see what we can do about the slowdown and what might be the issue.

[RwVision]

Thank you - same slowdown ratio happens in bigger scene I'm working with. Such slowdown is worth investigating. For the time being no one represented another example of clipper vs non-clipper rendering times to have more look into.
Would need to hop into 3.7 and compare, just don't have time.

[ivan.vardarov]

Hello RwVision,

What slows down your render is the "Fill Inner Cavities" parameter in the VRayClipper object. It is usually used when clipping closed geometry. To generate the 'caps' of the clipped geometry - we have to trace additional rays to check if the shaded point is inside or outside the mesh. Disabling this option should bring your render times back to normal.

[RwVision]

Thank you ivan.vardarov - that works perfect. I remember trying every option in bigger scene, but must have miss-figure it.

I think that the "Fill Cavities" should be off by default.
(First person to actually look at my setup - many thanks, that should gone like this on the first answer.)