Shaderhacker
Newcomer
You are in good hands!!
Arnold rocks! And I hope we can get it in-house eventually. Yep. Brute force is way better than cluttering up the pipeline with overhead. We are so sick of point clouds. I feel ya.
-M
Carmack on Ray Tracing & Rasterization
- Thread starter anexanhume
- Start date
You are in good hands!!
Arnold rocks! And I hope we can get it in-house eventually. Yep. Brute force is way better than cluttering up the pipeline with overhead. We are so sick of point clouds. I feel ya.
-M
Shaderhacker
Newcomer
You are right. But the GPU is hampered by memory - which automatically disqualifies it.
You are in good hands!!
I know, we've been on it since like early 2010, even contributed to some of the development effort. One of our dev guys actually left to Madrid to work on the renderer full time
Try using GI with fur in a RT. Or try motion blur with glossy reflections.
Oh, we do all that... we're now doing long hair and beards too
Not so many glossy surfaces though, that'll be the next project I guess.Not really inherent in forward projection, aka rasterization, hard shadows with an irregular z-buffer can be identical to hard shadows with raytracing.
anexanhume
Veteran
For now. Eventually available has to outpace target resolutions or main memory will become coherent to GPUs, no?
Cell missed its calling.
Shaderhacker
Newcomer
I hope so. We need at least 24G boards. I'm not sure how they would cache textures as well as hold complex dynamic data structures that update at least 30fps.
It'll be a while.
We don't even have enough bandwidth for drawing hair primitives. It's still too expensive to render hair the proper way.
-M
Billy Idol
Legend
Thanks Laa-Yosh for the info. How much is the maximum or average memory consumption while raytracing?
I am a bit surprised about the hardware you use. Two 6-core Xeon seems very very few resources? Does Arnold scale to much higher number of cores...say 100? Or what about using a Xeon Phi instead...maybe depends on memory usage?
I am a bit surprised about the hardware you use. Two 6-core Xeon seems very very few resources? Does Arnold scale to much higher number of cores...say 100? Or what about using a Xeon Phi instead...maybe depends on memory usage?
I have no idea about memory usage statistics, but the new 12-core nodes have 64GB in them.
As for using this number of CPUs and cores, again we have standard server racks and these are I think 2U machines. Not sure how many cores you can put in at that size.
There are also other issues about heat, and weight per square meter - again, the office building is a restored one and more than 150 years old, and the render nodes are on the first floor. We need to keep them distributed a bit and the aircon system has some funny issues during the summer when a certain tree releases these little flying thingies that tend to get sucked in and stop the airflow...
Then there's the network infrastructure and the storage and the various specifics and access patterns for the different type of machines and jobs... And I'm also completely at a loss about the cost and other efficiency issues but I'm sure our sysadmins have done their math and all. And we're still a relatively small shop not involved in VFX work, so our infrastructure can and has to be more simple and cheaper...
As for using this number of CPUs and cores, again we have standard server racks and these are I think 2U machines. Not sure how many cores you can put in at that size.
There are also other issues about heat, and weight per square meter - again, the office building is a restored one and more than 150 years old, and the render nodes are on the first floor. We need to keep them distributed a bit and the aircon system has some funny issues during the summer when a certain tree releases these little flying thingies that tend to get sucked in and stop the airflow...
Then there's the network infrastructure and the storage and the various specifics and access patterns for the different type of machines and jobs... And I'm also completely at a loss about the cost and other efficiency issues
but I'm sure our sysadmins have done their math and all. And we're still a relatively small shop not involved in VFX work, so our infrastructure can and has to be more simple and cheaper...Billy Idol
Legend
Thanks for the infos!
You're welcome!
Also, I've only included the hardware info to give some context to those rendering times. But also keep in mind the majority of our nodes are older and not as fast as these new 12-core systems, so the average frame times have to be judged in light of that.
Also, I've only included the hardware info to give some context to those rendering times. But also keep in mind the majority of our nodes are older and not as fast as these new 12-core systems, so the average frame times have to be judged in light of that.
That's not totally true on either count... filtered shadows can avoid the filter-size-based bias and thus only need a small precision delta to avoid numeric/self-shadow issues. And raytracing needs the same bias away from the polygon, so it's not really that different. Ray traced hard shadows can of course avoid some forms of aliasing that are difficult for shadow maps, but at a severe performance cost, similar to IZB. You pay for the hard cases either in performance or quality, there's no free lunch. Also I'll note that aliasing due to single-ray-per-pixel shadows is far worse in practice, and filtered shadow maps are a much more efficient way to solve that form.
I think for hard shadows shadow maps of sufficient resolution + cascades + some decent filtering will still win over ray tracing. For plausible soft shadows everything based on a single shadow map looks like crap, but conversely ray tracing requires way too many rays. Sigh... maybe stochastic rasterization, but it's just an expensive problem it seems.
Obviously any time you need truly incoherent rays you need ray tracing. The issue is if you have so little coherence you normally need a lot of rays to avoid noise. And filtering games can be played with either technique so if you're not looking for a physically correct result (which games are not), it's a bit of a wash there too.
The more interesting question to me is not whether ray tracing triangles is interesting, but rather whether ray tracing filtered/volumetric data structures is plausible. Adding just incoherent rays but requiring super-sampling is ok, but not super-compelling TBH, but adding constant-time volumetric lookups (a la. frustum or cone tracing) is definitely interesting...
Sure, but IMHO "interesting" ray tracing (i.e. incoherent) is about handling divergence and reconvergence, not FLOPS (although you still need some). This is why IMGs chip is much more about scheduling than ALUs - for good reason.
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Please understand that I'm no graphics programmer - when I talk about issues with shadow maps, it's from the user side, handling lighting technical issues for a few shots on a project that happened about 6 years ago. Also, it's not a realtime application, so it's about far higher quality and somewhat different circumstances.
Yeah no issues, and your statement is still generally correct that shadow maps require more cleverness and more tweaking (although they've gotten more automatic in the past few years, at least in the real-time space). Just wanted to clarify a few things since it's an area I'm very familiar with
the current trend with arnold is to try and render as much as possible in a single pass. splitting out passes into a lot of elements is old style that was done mostly for memory concerns. these days a objectid layer will take care of all the old style pass info (for cc).
Memory wise, raytracing isnt bad. its mostly geometry that chews memory. but even those are only called when in camera. render machines with 12gb ram are on the highside when it comes to farms. though I suspect that will change now ram is cheap. so any new boxes may have 24 - 32gb or so. some compositing boxes will have 32 - 64gb, but thats because those things keep multiple frames/layers in memory.
those dual cpu machines will generally just crunch 1 frame. rendering multiple frames at once on a single box means doubling the required ram, disk and network requirements. hence, rarely, if ever, done.
1280x544? im guessing you guys are doing cutscenes for a 360 title?
Shaderhacker
Newcomer
I can only rely on my experiences with PRMan's shadow maps, those were a b****... min distance, max distance, mid distance, bias, resolution, blur... And never enough memory, so I ended up animating the shadow camera to follow the action, and so on. Man, I hated it
Yeap. I feel your pain. We had the same problems. Very hard to light a whole scene with the scene is so large and your shadow map needed to be huge!
Shaderhacker
Newcomer
No one would ever only cast 1 shadow ray in ray-tracing. That's just asking for trouble.
The problem that Laa-Loosh and I run into is tryign to create a shadow map that will encompass the whole scene. You will *not* be able to compute a high enough shadow resolution in a reasonable amount of time or memory footprint. Also, shadow maps are pretty time-consuming to compute when hair or semi-transparent geometry is involed where you need to create deep shadow maps.
We had big problems with deep shadow maps when trying to render smoke in a Road Runner short where he created a long trail where the sun light cone just could not step through the volume with enough resolution to avoid the stair-stepping aliasing in the smoke (self-shadowing). We eventually went with Mantra and just ray-traced the shadows.
-M
