Guys, we need the "dynamic BVH" render back


Please read this threat too:

We desperately need the Dynamic Viewport BVH update back for Final Render.

It can’t be that we need to do screenshot capture for animations just cause the update in the viewport is real-time.
We need the dynamic BVH switch back in the Cycles render settings. It was there and worked beautifully for a long time.

People (me included) are frustrated that the sync takes now over 10-15 sec while the rendering on GPU nowadays is only 1-2 sec. So a 1000-1500% overhead in most cases.

I know that KWD works on an update system for fast sync, but already the dynamic BVH exists for the viewport and was used before 2.8. I don’t care if the BVH is super perfect if I have GPUs. The render speed margin is very negligible. We need the dynamic BVH switch back.
We want to have at least the switch there.


Many thanks.

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The dynamic BVH option is unlikely to come back as it is not supported by Embree and OptiX. What will be added is an option to avoid fully scene update and associated BVH rebuilds in animation renders.

Are you using OptiX for GPU rendering, and still finding BVH builds (excluding other preprocessing) slow? Or are you using CUDA or OpenCL?

Ok, i would even go back to CUDA and have Dynamic BVH than to wait for full build on Optix. It would still be faster. We are talking instant sync like back in the days of pre-2.8 with CUDA and dynBVH.

On the other hand, if i update something in the viewport even with Optix, its real time updated, why not getting a switch to use the viewport update BVH. Or just initialize a “viewport render mode” for final render. Even if it takes more RAM or “slower” render. Cause the GPUs are superfast and gone are the times when 512samples took minutes to justify the seconds of syncing.

Even if (for now till a better sync comes) the switch would be available only in CUDA mode, I would be more than pleased. Because with Optix the improvement is only around 25%, but with DynBHV I can save up to 1500% per frame avoiding sync.

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Though I do not have knowledge about this issue, but I suppose I actually see this problem
with one rig character + simple jiggle bone animation render with cycles.

I got new PC for 3d, then it have powerful glaphic nvidia card + powerful Thread intel CPU , then I test animation render with cycles X.

I confirm one frame render time is so fast…it was amazing. even though I keep to use render view,
I can pose my rig character, without many stress. but I notice, when render animation.
It took too long time to set up new frame scene until GPU start rende frame…

eg when I start render one frame, GPU Optix render took only 10 seconds after render start… (I check my GPU running in resource monitor, and rendered file are generated), after that blender change to next frame and start to build scene. it took almost 40 seconds to 1 minutes or more for each frame change I feel.

The rig character use some corrective shape keys (change with rig pose) + jiggle bone physics, and some modifier used to fit cloth. (eg shrink wrap + sub-D) . Then I just pose and set key to check IK bones.

I do not think old version blender took so long time when build next frame (but it took long time to render with cycles) I really do not know what setting may need to change, to render such simple animation for test…