Volumetric crashing or taking too long to render

i have been trying to incorporate volumetrics without crashing my blender file or making it take so so long that it’s just not realistic to use. (like 20 hours, and render mode crashes it). but without then like 20 minutes or something to render. i am wondering if anyone knows ways to get around this in an already somewhat heavy scene? it’s an outdoor scene and i just want some volumetric fog.

i have tested and rendered many scences with volumetrics,and often crashed.i guess you are useing GPU rendering?if so, then only reduce some volumetric bounces ,density ect can help.

the reason for a GPU crash is,that Windows GPU driver has a time counter,and if the GPU “hangs” to long (in this case takes to long to render a tiling), it resets to default display driver,because the counter time, written in the registry, is over that value.Windows now" thinks" your GPU hangs and reset its driver.

if you want to render anyway,you should select CPU rendering only for this heavy task,to avoid this GPU timeout resets.
Or reduce, in the render performance tab, the tiling for the gpu can help a little bit, if your GPU is fast enough for the tiling before the timeout reset starts.

i wish, we would have a function for this,that blender detect automaticly, that the volumetric is to heavy for GPU and jumps to CPU, before it crashs.

and a tip,dont start with very high densitys in the materials.start low as possible and increase as little as needed.

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You can increase TDR delay to like 15 seconds if you have this problem.

@SandraDau I’ve done many scenes with volumetrics and haven’t got any problems. Perhaps share an example .blend where you have problem.

Also please specify which version of Blender you are using.
If you are using 2.79b official release then, as @pixelgrip said, big tiles are best for gpu, but at the same time they may cause CUDA to hand for too long.
Try using 2.79 daily builds or even 2.80. It allows for CPU+GPU rendering and makes 32x32 tiles best in most cases, even for GPU, which should prevent any problems with sampling hangs.

Also, 2-3 volumetric bounces is enough for most cases (even 1 bounce is enough sometimes), don’t set it any higher. Density can be any value you want, it has nothing with performance.
If you are using volumes that have constant density - check in materials that it’s homonogenous. It does make computing faster. If you are using any 3D changes in volumetrics have that unchecked (heterogenous).

The final step of changing settings is in render settings. If you are computing volumetrics for small objects, for example 10x10 centimeters you have to change step size to something small enough to detect changes. And, on the other hand, if you are doing something big like 30x30 meters - you don’t have to compute checks for every milimeter. You can set it to 10 centimeters or more. This actually does speed up computing very much.

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Wow thanks a lot, lots of information and things to try!

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