3ds Max freezes after finishing render scene with ForestPack

[ZO6039]

I have a scene with terrain about 20x20km size, where I populate trees using ForestPack. I use two ForestSet objects which I use to select two layers of trees - leave trees and fir trees. I use my own collection of trees. All trees are VRayProxy objects. The total amount of trees for terrain is about 7 millions. The render is fast, it takes about 2:30 mins to render 1920x1080 frame. The problem is that when render of image is already finished and render progress bar shows 99% 3ds Max hangs completely. Rendering window remains open with progress bar on 99%. I can't do anything rather than open Windows Task manager and terminate 3ds Max process. I have 128 GB RAM installed on my PC. When I render frame I see that 3ds Max uses 63 GB of RAM and 70 GB of virtual memory. What is the problem and what should I tweak to fix it? I previously used Multiscatter for this scene. This is my first attempt to replace Multiscatter with ForestPack and it is not successful as yet. I really want to use ForestPack. Please help!

UPDATE: I replaced two ForestSet objects on two tree objects - one leave tree and one fir tree. The scene rendered fine without any issues and without changing any other parameters.

[ZO6039]

I was able to nail down the problem. The problem is with the VRayProxy tree model which crash max after finishing render with ForestPack even without tree materials. I created a simple scene using this tree model for your review. There are actually few tree models which cause the 3ds Max to hang up after render finish but I provide just one for the test. The problem happens when I render a big amount of trees - 5 millions. If I render just a few thousands then Max doesn't crash. I work in Max2024, V-Ray 6.1, ForestPack 8.2.3. I also tested in Max2022, V-Ray 5.2, ForestPack 8.2.3 with the same Max freezing effect at the end of render. Please take a look to the test file I saved in Max2021 version I shared on Dropbox https://www.dropbox.com/scl/fi/gvyqem8t9asrfl51l0fy0/BugReport_ForestPack_problem_tree_model.rar?rlkey=roe845bnqydohn7mqhg8ikzas&dl=0.

[iToo]

Hi,

Please take a look to this post. Probably it's the same problem.
Basically you must optimize your V-Ray proxies to be rendered as instances. If not, V-Ray takes a long time and memory to load and unload them.

I hope that helps.

[ZO6039]

Thanks for the information. I seems the same issue. I will try to follow the tip and will reply how it goes.

[ZO6039]

I have converted tree VRayProxy from 30 voxels to 2 as it was suggested and scene rendered fine. I have converted all VRayProxies with big number of voxels and I will test render scene with different plants. I am curious why Multiscatter plugin works fine in this case.

[iToo]

I have converted tree VRayProxy from 30 voxels to 2 as it was suggested and scene rendered fine. I have converted all VRayProxies with big number of voxels and I will test render scene with different plants. I am curious why Multiscatter plugin works fine in this case.

Sincerely, i don't know. Theorically this issue should affect to all plugins rendering proxies as instances, including the ChaosGroup tools (VRayInstancer, ChaosScater).
This solution was proposed by ChaosGroup, when we reported the problem to them. Also it has sense, because in recent V-Ray updates, proxies are generated by default "Optimized for instances" (using one single voxel), as shown in the attached image.

If Multiscatter uses a different technique for rendering proxies, which is not affected by this issue, we don't know.