How do you learn mantra?

[kfu]

Didn't find any good mantra tutorial online that is complete and explain optimization stuff. I guess we got Houdini document which is helpful in some way but can you guys recommend any good learning material for mantra? 

How do you guys learn mantra? Just experiment it yourself by trying and guessing all the sliders, or you learn other render which gets plenty of tutorials online and transfer your knowledge to mantra?

[davpe]

it's true that for mantra, there aren't really any recent detailed tutorials to watch (which is a shame). essentially thou, Mantra is the same thing as any other pathtracer. so if you already know how to use Arnold or Renderman you can translate a lof of this knowledge to Mantra. i have switched to mantra from using mental ray and arnold (like 5 yrs ago or so) and it didn't take me long to understand all the essentials. sure you've got some different names and options to turn on or off, sampling is split into a bit different controls etc. but I mean still you have your pixels and ray samples, ray limits, bucket sizes and so forth so it shouldn't be that big of a deal. reading houdini documentation helps a heaps. mastering Mantra is something that takes a long time thou, for the following reasons:

mantra has TONS of controls you can use to optimize (or de-optimize) the rendering process. That's sort of good and bad thing at the same time, depends on what you want and how good understanding of these settings you have. I like having a lot of control so I love Mantra for giving me million sliders and toggles that many users never touch. You can do stuff with it that can save your ass sometimes - because you can for instance render out some odd render pass that helps compositing tremendously and saves you from running an expensive render. Or sometimes you realize that if you use this in combination with that, you can very easily render an effect that would be otherwise painful or time consuming to do. Unfortunately, "uneducated tinkering" can equally well turn your "grey sphere on a checkerboard" into rendering nightmare that takes 90 hours to complete - your call  Some people are driven crazy with that bcs they just want to set the slider to "good quality", hit the render button and get that picture done (can't blame them).

One objectively BAD thing in Mantra, especially for new users, is that among it's numerous parameters (half of which is actually "hidden", and you have to go to Edit rendering parameters interface to access it) there are a few inconspicuous ones that can make a big difference in how long and in what quality your picture actually renders (in some cases), and there is no way to know unless you're told, or you spend time figuring out why this particular scene eats up 100GB of ram if there is apparently no reason for that. Then you discover this hidden parameter having completely inappropriate default value (which turns out to be an issue if you render more than certain amount of texture data in your scene for example). i personally think stuff like this is one of the main reasons that makes many users turn to some easier-to-grasp solutions like Arnold, that is quite limited in what you can do with it, on the other hand thou, it's very easy to use, and you don't have to be an expert user to get quite consistent and predictable results.

So my advice on learning mantra is, learn how raytracers are working in general, then read the docs and then do a lot of experiments with things you're not sure about.

Having said that, in this article you can read about some of those nasty hidden parameters: https://vfxbrain.wordpress.com/2016/03/16/mantra-tips/

And maybe some more tips here: https://vfxbrain.wordpress.com/category/rendering/

cheers.

Edited December 21, 2018 by davpe

[kfu]

@davpe Thanks David, that's very informative.  It's indeed a shame that there is no one actually teaching mantra online(only some pretty old ones from sideFX), which probably is one of the reasons that mantra was not very popular among regular users. 

I have some basic knowledge of Arnold and ray tracing concept before switching to use Houdini, but still I found it confusing looking at all the tabs mantra has. (sampling and limits tab are all I have used for now)

So, I was doing a test render yesterday, but even such a simple scene took my computer 50 mins(10 core E5 2640 with k4200), don't know it's suppose to be this slow or I did anything wrong here( all light with default settings , 4X4 pxiel samples, diffuse and refelction quality setting to 2 , diffuse limit to 1). I thought this was a very low setting but still it take such a long time. Is mantra not good at handling simple scene?

 

also there are some issues with the indirect diffuse, dont know where those straight lines come from and the rectangle noise shape behind the figure.

 

 

BOSIO_fix.OBJ

figure_render.hipnc

[kfu]

So I tested a new one, just bumped the pixel samples to 5X5, and the render time increased to over 2 hours, which is insane. I think I definitely missed something out. One thing is that  the geo is kind heavy with lots faces,maybe I will try some lower ploy geo later

[davpe]

ok so let's see. number of poly is not an issue. issue was an unreasonably high render settings, even thou you felt it's low. in your picture, there isn't very high contribution from indirect reflection rays, yet you've had reflection ray depth set to 4 and on top of it, reflection quality set to 2. those were your main slow down factors. I was able to render exactly the same looking picture in 8 mins with ray limits to 1 and quality to 1. generally I mostly start with ray limits at 0 and then I don't go beyond 1 even for the final renders unless there is a significant visual difference and I can't achieve it other ways. your scene is just too simple to benefit from multiple reflection bounces but still those had to be computed by Mantra, and have gotten exponentially more expensive to render. it would make more sense, by the way, to increase number of diffuse bounces to 2 as you've got a huge white background there that would bounce a lot of light around (if you wanna go fancy - see the last pic, 1 refl bounce, 2 diffuse bounces, render ~11 mins).

reason for your background having artifacts was it being nurbs surface. I have never used nurbs surfaces for rendering, so not sure why exactly it was rendering wrong but when I converted to polygons shading turned out fine.

and just for info, this was rendered on my laptop with 4-core i7-7700HQ. so yours should be even a bit faster.

cheers

Edited December 22, 2018 by davpe

[bunker]

@kfu, you can get the same look with 3 AA samples and reflect limit 1, just increase your max samples to 16
to convert your NURBS geometry to polygons use a convert SOP.

LEFT: your scene: 6 min 50s (on i7-5930K 6 cores @ 3.50GHz, H16.0 Ubuntu 16.04 )
MIDDLE: 4 mins 45s figure_render_445.hipnc
settings: pixel samples 3x3, max ray samples 16, global quality 1, diffuse quality 1, reflection quality 1,
reflect limit 1, diffuse limit 1, everything else at 0
RIGHT: 14 mins 22s figure_render_1422.hipnc
3x3 pixels samples, max ray 24, reflect limit 1, diffuse limit 4, diffuse quality 2

there are some good tips in this Materclass on Mantra Rendering (after 3:36)
_https://vimeo.com/143618200
 

Edited December 24, 2018 by bunker

[kfu]

@davpe thanks, that's very helpful!

@bunker yeah, I was rendering it  with too high settings,thanks for the info.