Fix #70114: Cycles: Particle systems missing in headless multiview render #120543

Lukas Stockner · 2024-04-12T01:26:26+02:00

Lukas Stockner commented

2024-04-12 01:26:26 +02:00

The problem here was that free_data_after_sync frees the particle cache in headless or locked-UI mode, but the second view doesn't regenerate them.

For multi-view renders, dropping caches is a tradeoff between compute and memory - dropping allows to reduce peak memory usage, but requires recomputation for the next view. With the current design however, dropping is not something that is easily achievable anyways (see the referenced bugs). So until something more reliable and better fitting is implemented, keep the data from Blender side until the last view.

Since free_data_after_sync doesn't do anything for baking or viewport renders anyways, it's easiest to just move this out into BlenderSession::render since that already checks whether another view is still outstanding.

Also fixes #73221 and #107589.

The problem here was that `free_data_after_sync` frees the particle cache in headless or locked-UI mode, but the second view doesn't regenerate them. For multi-view renders, dropping caches is a tradeoff between compute and memory - dropping allows to reduce peak memory usage, but requires recomputation for the next view. With the current design however, dropping is not something that is easily achievable anyways (see the referenced bugs). So until something more reliable and better fitting is implemented, keep the data from Blender side until the last view. Since `free_data_after_sync` doesn't do anything for baking or viewport renders anyways, it's easiest to just move this out into `BlenderSession::render` since that already checks whether another view is still outstanding. Also fixes #73221 and #107589.

Lukas Stockner added this to the Render & Cycles project 2024-04-12 01:26:42 +02:00

Lukas Stockner force-pushed fix-instance-cache from 82a78992a2 to 2353dd1fdc

2024-04-12 01:26:48 +02:00

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Lukas Stockner requested review from Brecht Van Lommel 2024-04-12 01:27:09 +02:00

Lukas Stockner requested review from Sergey Sharybin 2024-04-12 01:27:09 +02:00

Lukas Stockner referenced this pull request

2024-04-12 01:29:22 +02:00

Particle System missing on right eye when renderd via terminal #70114

Sergey Sharybin reviewed 2024-04-12 15:03:30 +02:00

Sergey Sharybin left a comment

I think code-wise it is the best we can do for now, without going into deeper refactors. What I am not sure about is this:

For multi-view renders, there's no point in dropping the cache if we'll render another view anyways, so just keep it until the last view.

The wording might need to be tweaked, because intuitively it can be useful to reduce the peak memory even for multi-view render in-between of views. Ideal flow would be something:

Evaluate data on Blender side
Copy it to the Cycles side
Drop caches from Blender side
Load images, build BVH, compile shaders, and all other memory hungry operations
Update camera matrix for another view
Render from the new camera perspective

However, it is not something that fits easily into the current approach of memory saving strategy. There is no need to change it, but maybe wording could be changed to someyhing:

For multi-view renders it would be nice to lower peak memory usage, but it is not something that is easily achievable with the current design. Until something more reliable and better fitting is implemented keep the data from Blender side until the last view.

It is a proposal, can tweak wording as you feel makes more sense.

I think code-wise it is the best we can do for now, without going into deeper refactors. What I am not sure about is this: > For multi-view renders, there's no point in dropping the cache if we'll render another view anyways, so just keep it until the last view. The wording might need to be tweaked, because intuitively it can be useful to reduce the peak memory even for multi-view render in-between of views. Ideal flow would be something: - Evaluate data on Blender side - Copy it to the Cycles side - Drop caches from Blender side - Load images, build BVH, compile shaders, and all other memory hungry operations - Update camera matrix for another view - Render from the new camera perspective However, it is not something that fits easily into the current approach of memory saving strategy. There is no need to change it, but maybe wording could be changed to someyhing: > For multi-view renders it would be nice to lower peak memory usage, but it is not something that is easily achievable with the current design. Until something more reliable and better fitting is implemented keep the data from Blender side until the last view. It is a proposal, can tweak wording as you feel makes more sense.

Brecht Van Lommel approved these changes 2024-04-15 15:00:16 +02:00

Brecht Van Lommel left a comment

Functionally seems fine, but would be good to update the comment as suggested.

Lukas Stockner merged commit c9c777ddaa into main

2024-04-15 17:41:05 +02:00

Lukas Stockner referenced this issue from a commit

2024-04-15 17:41:10 +02:00

Fix #70114: Cycles: Particle systems missing in headless multiview render

Lukas Stockner deleted branch fix-instance-cache

2024-04-15 17:41:13 +02:00

Lukas Stockner commented

2024-04-15 17:42:31 +02:00

Good point about that sentence, thanks - dropping caches might indeed be worth it to reduce peak mem usage. I've updated the PR and commit message.

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Fix #70114: Cycles: Particle systems missing in headless multiview render #120543