Bump mapping and displacement in Vray vs. Modo's native engine.

[GidPDX]

I was just doing some tests and noticed that on high frequency areas, when using procedurals, displacement was nearly as fast or faster than using the same texture as a bump.

This makes sense in a way, but I was wondering if Vray, like some other render engines (mental ray, arnold) calculated bump in more ways than it seems MODO does, and is therefore more expensive than in MODO, and if so, do many people use displacement instead?

I know there are a lot of variables at play here (scene size, RAM needed to render, types of material settings used etc.) but I'm just curious.

[vladimir.nedev]

That's strange that displacement is faster than bump.
When you have displacement, it needs to calculate the normals of the displaced surface while shading, and this calculation is basically the same thing as computing bump mapping.
It's probably a matter of the image with displacement being easier on the image sampler and generating less image samples.
For comparisons like this, when the final images do not match, you should use the Fixed sampler.

Greetings,
Vladimir Nedev

[GidPDX]

Thanks Vladimir, I'll look into fixed sampling. I was just reading about fix rate the other day, but wasn't sure how much of it still applied with the new sampling methods that went into 3.3. I see there are still times to make use of it!

I was thinking that it was because displacement has some hard constraints on how much something could get divided. If the surface change was very small, then there would be very few extra divisions formed, and fewer polygons, and not too many extra samples. With a procedural texture, I was thinking that the refinement could go on to sub-pixel levels, and that this might describe why displacement is nearly as fast.

Subdivision and rendering of those surfaces time vs. shading samples I guess. I'm probably way off the mark though. That said, using a fixed rate should allow me to see if that theory is true or not so thank you for the suggestion- I'll give that at try.