Coder Corner

I am very happy to announce the first public release of PEEL - the Physics Engine Evaluation Lab.

I briefly mentioned it on this blog already, here.

Source code is included for the main program and most of the PINT plugins. That way you can create your own test scenes and check that everything is done correctly, and benchmarks are not biased.

Pre-compiled binaries for most of the plugins are provided, for convenience. Some of the binaries (in particular Havok plugins) have been removed, since it is unclear to me if I can distribute them or not. On the other hand some plugins are currently only available as binaries (Opcode2, ICE physics..).

Please refer to PEEL’s user manual and release notes for more information.

Have fun!

Download link

(As usual, the bitcoin tip jar is here if you like what you see )

https://developer.nvidia.com/content/latest-physx-source-code-now-available-free-github

Note that contrary to what the post says, this is only the second best version (3.3.3). We are currently working on 3.4, which already contains significant changes and significant speedups (for example it includes Opcode2-based mesh collision structures, which provides faster raycasts, overlap and sweep queries). I think we will eventually open source 3.4 too, when it is released.

EDIT:

I’ve been reading the internet and receiving private emails after that. Apparently what I wrote is technically wrong: it is not “Open Source” because it does not have a proper open source license, it comes with a EULA, etc.

I notice now that both NVIDIA’s press release (above) and EPIC’s (here) are carefully worded. They actually never say “Open Source”, or even “open source”. They just say things like:

“NVIDIA opens PhysX code”

“PhysX source code now available free”

“The PhysX SDK is available free with full source code”

The weird thing then, is that many internet posts do the same mistake as I did, and present the news as if PhysX was indeed “Open Source:

http://techreport.com/news/27910/nvidia-physx-joins-the-open-source-party

http://www.dvhardware.net/article62067.html

http://forums.guru3d.com/showthread.php?p=5024001

https://forum.teksyndicate.com/t/physx-made-open-source/75101

http://hardforum.com/showthread.php?t=1854357

(etc, etc)

Why is everybody making this mistake, if indeed none of the official press releases actually said that?

I’ll tell you why.

That’s because the distinction between “NVIDIA opens PhysX source” and “PhysX is open source” is so subtle that only pedantic morons misguided souls would be bold enough to complain about it when given something for free.

Give them a finger, they’ll take the whole hand, and slap you with it.

I have the feeling this is the only industry where people are so insane and out of touch with reality. You’ve given a free Porsche and then you complain that it is not “really free” because you still need to respect the “strings attached” traffic code. Hello? Just say “thank you”, enjoy what you’re given, or go buy a Ferrari if you don’t like Porsche. Jeeez.

Here is another paper I wrote some time ago. If you are struggling with invalid contacts against internal edges in your rigid body simulation, this one might help.

http://www.codercorner.com/MeshContacts.pdf

As usual, the bitcoin tip jar is here if you like what you read

I wrote this last year. Enjoy.

http://www.codercorner.com/ZeroByteBVH.pdf

As usual, the bitcoin tip jar is here if you like what you read

EDIT:

“Any sufficiently advanced technology is indistinguishable from magic”

If a game uses PhysX, it does not mean you will notice it. It might not have obvious PhysX effects in it. It might not have cloth, or PhysX particles, or water effects, etc.

These are just flashy/trendy effects that are easy to advertise/sell/etc for the marketing people. The kind of stuff that gamers care about, maybe. But this is not the important part.

The most important part is the one that you don’t see. The one that makes you game playable at all.

When you fire a gun in a FPS, that’s PhysX (”raycast single” scene queries).

When NPCs/AI see you, that’s PhysX (”raycast any” scene queries).

When many NPCs properly interact and avoid going through each-other, that’s PhysX (broadphase).

When your character simply moves in the level, that’s PhysX (”sweep” scene queries, or even PhysX’s character controller).

It’s not just about ragdolls or particle effects. PhysX is also there supporting the invisible foundation upon which everything else is built.

https://twitter.com/AnthonyYakovlev/status/522097473113051136

“Interestingly enough, on desktop-like platforms, PhysX3 is faster than Box2D”

http://atforums.mobi/msg.php?threadid=2403672&catid=8&rnum=25

So, yes, PhysX 3 is well optimized (and PhysX 3.4 even more). But I’d like to go back to the old “2.8.4 is crippled” myth, since this is mentioned here again (”PhyX 2.x was garbage because a ton of sites outed nVidia for using x87 and lacking multi-threading on the old CPU code”).

This is not what happened, at all. I’m afraid you’ve been spoon-fed utter bullshit by websites that love an easy dramatic headline. I suppose it makes a good story to reveal nasty things about “big” companies like MS, Google, Apple, Nvidia, whatever. But the reality behind it here is terribly mundane and ordinary. There is no story. There is no conspiracy. There is no evil plan to cripple this or that.

NovodeX (on which PhysX was initially based) was written by Adam and me. The code was super optimized, to the best of my knowledge at the time. But it did not support SIMD or multi-threading. At that time, none of us knew how to write SSE code, and I also had no experience with multi-threading. Also, IIRC SSE2 was not widely supported (only SSE). From our perspective the gains from SSE seemed limited, using SSE2 would have made the SDK incompatible with most of our users’ machines, and we simply didn’t have the time or resources to learn SSE, support SIMD and non-SIMD versions, etc.

Then came Ageia. In the beginning, we had to make the SDK feature-complete before thinking about making it run faster. NovodeX did not even support convex objects! And that’s the first thing I had to implement in the post-NovodeX days. NovodeX was the fusion of two hobby projects from two independent developers. In a number of ways the result was still just that: a hobby project. We loved it, we worked very hard on it, but we basically had no customers and no actual games making actual requests for random features that are actually useful in games. This all changed when the hobby project became PhysX under Ageia. That’s when it became an actual product. An actual middleware. With actual customers actually using the thing in actual games. Especially when it got picked up by Epic and integrated in the Unreal engine. Suddenly we got TONS of bug reports, feedback, feature requests, you name it. Tons of stuff to do. But as far as I can remember nobody asked for “the SSE version”, and so none of us worked on it. There was no time for that, no incentive to worry about it, and we still didn’t have a SIMD expert at the time anyway. We briefly looked at the new compiler options in MSVC (/SSE2, etc) but the gains were minimal, maybe 15 to 20% at best. If you believe that recompiling with such a flag will magically make your code run 4X faster, I am sorry but you are just a clueless fool misguided soul. At the time, with the available compiler, we never saw more than 20% in the very best of case. And most of the time, for actual scenes running in actual games, we saw virtually no gains at all. Enabling the flag would have given us marginal gains, but would have increased our support burden significantly (forcing us to provide both SIMD and non-SIMD versions). It would have been stupid and pointless. Hence, no SIMD in PhysX2. Simple as that.

For proper SIMD gains you need to design the data structures accordingly and think about that stuff from the ground up, not as an afterthought. And this is exactly what we did for PhysX3. After making PhysX2 stable and complete enough, after making it a real, useable, feature-complete middleware, it was finally time to think about optimizations again. It took time to make the software mature enough for this to be even on the roadmap. It took time for us (and for me) to actually learn SIMD and multi-threading. It took time for compilers to catch up (/SSE2 on latest versions of MSVC is way way way better and produces way more efficient code than what it did when we first tried it). It took time for SSE2 support to spread, and be available in all machines (these days we only have a SIMD version - there is no non-SIMD version. It would have been unthinkable before). And still, even after all this happened, a better algorithm, or better data structures or less cache misses, still give you more gains than SIMD. SIMD itself does not guarantee that your code is any good. Any non-SIMD code can kick SIMD code’s ass any day of the week if SIMD code is clueless about everything else. Anybody claiming that PhysX2 is “garbage” because it doesn’t use SIMD is just a ridiculous moron (pardon my French but hey, I’m French) clearly not a programmer worth his salt (or not a programmer at all for that matter).

So there was no crippling. The old version is just that: old. The code I wrote 10 years ago, as fast as it appeared to be at the time, is not a match for the code I write today. Opcode 2 (which will be included in PhysX 3.4) is several times faster than Opcode 1.3, even though that collision library is famous for its performance. It’s the same for PhysX. PhysX 2 was faster than NovodeX/PhysX 1. PhysX 3 is faster than PhysX 2. We learn new tricks. We find new ideas. We simply get more time to try more options and select the best one.

As the guy in the article says, PhysX3 is so fast that it changed his mind about the whole GPU Physics thing. Does that sound like we’re trying to promote GPU Physics by crippling PhysX3? Of course not. And in the same way we did not try to promote Ageia Physics by crippling PhysX2. We were and we are a proud bunch of engineers who love to make things go fast - software or hardware.

EDIT: I forgot something. Contrary to what people also claim, PhysX works just fine on consoles and it is a multi-platforms library. That is, writing SIMD is not as easy as hardcoding a bunch of SSE2 intrinsics in the middle of the code. It has to be properly supported on all platforms, including some that do not like basic things like shuffles, or do not support very useful instructions like movemask. Converting something to SIMD means writing the converted code several times, possibly in different ways, making sure that the SIMD versions are faster than their non-SIMD counterparts on each platform - which is not a given at all. It takes a lot of time and a lot of effort, and gains vary a lot from one platform to the next.

In my previous posts I mentioned some R&D code I wrote for large stable stacks. I can’t talk much about the algorithms involved, for obvious reasons, but I can share a small proof of concept demo.

Click here to download.

(Note: don’t let the “CUDA Test” title fool you, it’s all CPU)

I got a bunch of questions about my last series of blog posts so I thought I’d add a quick note here - at the risk of confusing people even more.

The figures I posted are for the CPU part of PhysX only. This does not concern or affect the GPU parts of PhysX in any way. Those things are orthogonal. If we optimize the CPU parts and get a 10X speedup, it does not mean your GPU will suddenly provide 10X less value, because it is running others parts of PhysX anyway - neither the rigid bodies, nor the raycasts/sweeps.

Only a few features are GPU-accelerated, e.g. cloth or particles, mainly because they are the ones that map well to GPUs, and they are the ones for which the GPUs provide real X factors.

Now as shown in the recent “destruction video” I posted, people here are also working on GPU-optimized rigid bodies. This new module is called “GRB”, and it is currently not part of PhysX. But it does provide a speedup compared to our current CPU solution. In other words, it is still faster than PhysX 3.3 on CPU. You might have a hard time believing it, but people are trying to be fair and honest here. One of our tasks is to optimize the CPU rigid bodies as much as we possibly can, just to make sure that the GPU rigid bodies do provide some actual benefit and speedups. If you don’t do that, you release your GPU solution, it’s slower than a CPU solution, and you look like a fool. Like AGEIA. We are not making that mistake again. The CPU solution is here as a reality check for ourselves. I suppose we could just use Bullet or Havok for this, but… well… we think we can do better

Meanwhile, it is correct that the features that do work on GPU are currently only working on NVIDIA cards, simply because they are implemented using CUDA. There are both obvious political and technical reasons for this. It should be pretty clear that at the end of the day, NVIDIA would like you to choose one of their GPUs. If you are actually complaining about that, then there is little discussion left to have. Of course they want to sell their products, like every other company in the world. And of course they are going to use their own technology, CUDA, to do so. To me this is pretty much the same as what we had in the past with D3D caps. Some cards supported cubemaps, or PN-triangles, or whatever, and some didn’t. GPU PhysX is the same. It’s just an extra cap supported by some cards, and not by other. Complaining about this is silly to me. It would be like complaining that ATI didn’t make any effort to make PN-triangles work on NVIDIA cards. Seriously, what?

The deal is simple. NVIDIA gives you a free, efficient, robust physics engine. In exchange, if possible, add some extra GPU effects to give people an incentive to buy NVIDIA cards. Fair enough, right? I don’t see what the fuss is all about.

—-

Anyway, the usual disclaimer applies here: I’m not a spokesperson for NVIDIA, what I write are my own thoughts about it, and for all I know I may be completely wrong about their intentions. What I know for a fact though, is that most of the stuff I read online about PhysX is just completely insane wrong.

I’ve been optimizing rigid body simulation in NovodeX/PhysX for a long time now, and there’s no big conspiracy behind it. Again, all those engines are free and publicly available so I invite you to run your own experiments, do your own benchmarks, and see for yourselves. We really have nothing to hide.

Part1: PEEL

Part2: Rigid bodies (box stacks)

Part3: Rigid bodies (convex stacks)

Part4: Rigid bodies (piles)

Part5: Rigid bodies (compounds)

Part6: Rigid bodies (meshes)

Part7: Joints

Part8: Raycasts vs simple shapes

Part9: Raycasts vs meshes

Part10: Sweep tests

Part11: More sweep tests

Part12: Final test and conclusion

Addendum