Hidden tyFlow object perfrom simulation on render stop with Corona only

[v.p.vlasenko]

Hi,
problem - clean scene, simple tyFlow object is hidden (as simple as birth operator only, so it won't render anyway), changing frame to let's say 50 doesn't perform simulation, starting render (interactive or production) as well doesn't perform simulation, but when I stop or cancel render, tyFlow start simulation up to current frame (50).

Tyson said

tyFlow objects simulate their result when Max queries their base object for a result

...

hiding a tyFlow object does not guarantee Max will never query it.

I tried Arnold and Scanline - no sim on render end, so probably some problem with Corona?

[Avi]

Hi,

I am unable to repro this on my end using 3ds Max 2024, Corona 12 HF 1 and latest version of Tyflow. Is this happening in some specific sim you are doing or this is happening even in a very simple sim also?

Is it possible for you to send your scene file so we can investigate this further?

you can send your scene by starting a ticket here: https://support.chaos.com/hc/en-us/requests/new

[v.p.vlasenko]

Hi,

I noticed it in a specific sim, but when I tried to figure out what's going on I found that it happens in such a way in the simplest scenes, like in the video below

I don't think I need to send such scene to you.

I forgot to add my specs in the original post:
2025.3
latest corona daily
tyflow 1.118

[Avi]

Hi,

I was able to repro this issue and have logged in our system to be further reviewed by our devs.

(Report ID=CMAX-1466)

[Avi]

Hi,

After our review, we found that, this is happening even without Corona. This is a tyflow bug not Corona. Please see the video attached.

[v.p.vlasenko]

You did it wrong))) What's in your video is expected behavior. Selecting the hidden tyflow object will update the simulation up to the current frame - that's correct, at least that's how it works.

Check my video again:
1 - tyflow is selected from the start (I didn't deselect/select it again) - the sim happens only when Corona stops rendering, but not with Scanline and Arnold.
2 - In the end I deselected it and still it updated the sim after Corona stopped rendering.

So what's the problem with this?
I have a lot of tyflow objects in the scene with some simulations, which I baked into objects or converted to forest pack for example. Now those tyflows are hidden, I don't interact with them. Save the scene, close max, open max, working. Tyflow objects are hidden so no sim happens. Now I need to do some test render and what do I get on render end? All those tyflow start simulations one by one.

You can check it in the scene from your video, change the birth amount to 5000000, left it hidden. Save scene, then open it. Don't select tyflow. Change the frame to 50 and render with Arnold then switch render to Corona and render again, you'll see difference)

[romullus]

Why don't you just deactivate tyflow sims that you don't need instead of hiding tyflow object? That way it should not be updating sim anymore.

[Avi]

You did it wrong))) What's in your video is expected behavior. Selecting the hidden tyflow object will update the simulation up to the current frame - that's correct, at least that's how it works.

Check my video again:
1 - tyflow is selected from the start (I didn't deselect/select it again) - the sim happens only when Corona stops rendering, but not with Scanline and Arnold.
2 - In the end I deselected it and still it updated the sim after Corona stopped rendering.

So what's the problem with this?
I have a lot of tyflow objects in the scene with some simulations, which I baked into objects or converted to forest pack for example. Now those tyflows are hidden, I don't interact with them. Save the scene, close max, open max, working. Tyflow objects are hidden so no sim happens. Now I need to do some test render and what do I get on render end? All those tyflow start simulations one by one.

You can check it in the scene from your video, change the birth amount to 5000000, left it hidden. Save scene, then open it. Don't select tyflow. Change the frame to 50 and render with Arnold then switch render to Corona and render again, you'll see difference)

That was one of our observations that it sims with simply selecting and deselecting also, other than that our devs investigated that the calls made by Corona are standard and those should not have caused the tyflow to start the simulation especially when its hidden. So, the bug is not in Corona as far as we know. Yesterday, I wrote a email and shared this info with the developer of tyflow. If I hear back from him, I will update here.

[v.p.vlasenko]

Thanks, I hope it'll be solved.

Why don't you just deactivate tyflow sims that you don't need instead of hiding tyflow object? That way it should not be updating sim anymore.

This was just an example, but situations vary and it is a very annoying problem.
+ it's obviously more convenient to hide layers with sims instead of disabling each of them.

[Avi]

Hi, So i received some updates from the dev of tyflow and here is what they said:

TyFlow updates even when hidden because 3ds Max queries objects for updates (EvalWorldState) even if they are hidden, just like any other object in the scene.

This can happen when clicking on a tyFlow node (even if hidden), stopping or canceling a render (because 3ds Max (EvalWorldState) updates the scene), scrubbing the timeline or changing the scene time, other situations where Max calls for an update.

So, in short, this is not a bug but an expected behavior of tyflow. TyFlow updates when needed because other objects might depend on it.

If you don’t want a hidden tyFlow object to update, then you can set tyFlow’s update mode to "manual".

This way, it won’t update unless you refresh it manually.

I hope this helps.

[v.p.vlasenko]

Thanks for the reply, but, as the topic name says - it happens only with Corona.

In my video tyflow doesn't update after Scanline and Arnold, just after Corona.
I don't have Vray, so I asked a friend to check and he confirmed, the same story on his side - Vray, Arnold, Scanline are ok, but not Corona.

So 3 vs 1. Doesn't look like expected behavior.

[Avi]

Hi,

I have checked this with other renderer's also and I can confirm this is same with V-Ray and Redshift also. You can reach out to autodesk support regarding this as this is related to 3ds Max itself.

[v.p.vlasenko]

Hi Avi,

not sure how you checked, but in my video it happens with Corona only.

Anyway, here is another video - different PC, different 3dsmax version, different corona version and the distance between my PC and this one is around 13000km.

Again - the problem is with Corona only, V-Ray and scanline are ok. Same for Arnold (there is no Arnold in this particular video, but it was in a previous one I received, so Arnold is ok too)

I can confirm this is same with V-Ray

Looks like it's not the same

[Avi]

Hi,

Please see the video attached.

[v.p.vlasenko]

But these are GPU renderers in your video, so maybe some difference here.

Anyway, we have:
V-Ray CPU, Scanline CPU, Arnold CPU on one side
V-Ray GPU, Redshift GPU and Corona CPU on another

So to me it doesn't look like it is related to 3dsmax. Looks like it's related to a particular renderer.