Mecanims memory requirements make it unusable for mobile games

When Mecanim was released we were pretty excited and soon switched to the new system. Now, several months later, we deeply regret that decision. We will have to switch back to the legacy system, scrapping weeks of work with even more weeks ahead of us. Here is why:

Our game is an MMO with lots of animations and lots of characters running around. It needs to run on the iPad 3 (among other platforms). A few days ago we ran into memory problems on the iPad. Thanks to Unitys new memory profiler (which is very cool!) we quickly identified the problems. To our great surprise, the Mecanim Animator component of every single character needed almost 7 MB (!!) or RAM. That means that 15 characters (which is not a lot for a game like ours) alone eat > 100 MB, crashing the iPad.

We could not quite believe it and started digging around, comparing our project to Unitys Mecanim samples. We were clearly doing something wrong. Turns out we did not. Here is what we found:

• Every single State in an AnimationController needs ~11KB. (Per Animator INSTANCE, for whatever reason!)
• Every single Animation in a BlendTree needs ~15KB. (Again, per Animator instance.)
• This is true even if you use the same animations multiple times. 10 entries in the blend tree, even if it’s really just two different animations, amount to ~150KB.
• A second layer roughly doubles the memory requirement of the Animator (as if you copied all states and blend trees from the other layer.)

And that is the ugly truth. We have ~80 character animations, 2 layers, 7 blend trees. Amounts to 7 MB per character instance. Bye bye, iPad.

The whole thing is just crazy. Even if we accept that states and blend trees need meta data – why does all of that data exist per instance?

tl;dr: Mecanim is not production ready. It may work for samples and student projects, but it does not for real world mobile games.

Dear Unity Team: Is this something you are working on? Is this fixable in the near future or do we really need to abandon Mecanim alltogether? (And please feel free to contact us for more information!)

 

I don't know exactly what the numbers are for which versions of Unity. But those numbers seems much too high. I know the actual data contained in the Animation Controllers, Animations and Avatars are mere assets. Certainly there is book keeping on top, but 11k per state doesn't sound right to me. Actually there should be no per state cost as far as I can see.

I can only recommend you file a bug and attach a project that will reproduce the memory usage. It doesn't have to be the full mmo, just any project that clearly shows this radical memory growth you're describing.

Yes, we're constantly improving on Mecanim and is still making significant improvements on it. Since its initial development the team has only grown.

 

Thanks for the swift reply. I agree that these numbers are WAY too high. The overhead per instance should certainly be only a few KB, not MB.

I have filed a bug report, complete with example. (Ticket 556626)

The problem is acutually easy to reproduce using any existing mecanim project. We used the GDC 2013 sample for sake of simplicity.

- disable the StartRecord() and StopRecord() functions in Recorder.cs. They eat a lot of memory and are not needed in this example.

Start the game, collect the popsicle, wait for the bears to spawn. Now open the memory profiler and check the "Scene Memory" tab. We are interested in the Animators of the bears.

Observe that even in the unmodified sample, every NPC Animator uses 122.7KB (already quite high if you ask me).

Stop the game. Now edit the Animator controller of the NPC and add a blend tree. Add the idle anim 10x to the blend tree. It does not have to be connected or anything. Start the game, repeat the measurement like above. Every bear now uses 175.7KB.
Copy the blend tree 9x. Memory consomption is now 0.6MB per bear.
Add 20 empty states, again no need to connect anything. Memory is now at 0.7MB per bear. You get the idea.

I would like to stress again that this problem is very real. We have 80 animations, two layers and a few blend trees. The animator of our character currently needs 7MB and we need to do 20-30 characters (>200MB) ... on an iPad

I would really appreciate any info you can give me. If this is not fixed soon, we will have to write our own animation system on top of the legacy system.

 

That is an excellent question! You need to create certain lookup structures, no doubt about that. But you need that once per clip/skeleton-pair, certainly not per Animator instance and certainly not multiple times for identical clips in a blend tree.

Quite frankly, "2x less memory used by Animator instances in some cases" is not gonna cut it.

We have 100 - 200 MB memory usage for Animators. Total animation data size is ~7 MB. "Acceleration structure" seems to be a bit of an understatement here.

Idea: if you let us take a look at the code we can help to improve it. We have several experienced engine devs on the team (including myself), so this is a serious offer. If you guys cannot solve this soon we'll have to look for an alternative anyway.

 

Hi pierrepaul,

even if you make it faster by factor 2, this does not change anything. To be en pair with the compeititon you have to make it faster by factor 100, just to make clear how far you are away from fixing this issue.

So overall it stands that Mecanim is not useful for larger iOS productions and honestly you should have a warning somewhere making developers aware of this massive memory usage!

To me it seems as if you released a product which still belongs into alpha/beta testing. However the offer still stands that we can have a look at your problems. We have a few very experienced developers here working on a larger project: https://www.facebook.com/albiononline

We are also fine with signing any NDA's or similar, we just want this problem to be fixed asap.

Kind regards,
Stefan

 

Hi All,

Very interesting thread.Is there any progress on "mecanim for mobile" subject?

Regards,
Patryk

 

I just subscribed to this thread. I'd like to know more, too. We are exclusively working on mobile games.

 

Excellent news! Looking forward to the fixes and new enhancements. Mecanim has really improved my workflow.

 

Are there plans for more memory optimizations, specifically around 2D blend trees? Currently, we are @ 1.7MB/player and we have 30 players. This is due to a large 2D blend tree we have for locomotion. Unfortunately there is little that we can remove from it and maintain the desired functionality.

Thanks,
Chris

 

Bump.

 

Has there been any development on the subject?
Any developers willing to share recent experiences with mecanim for mobile?