2.79 Cycles render is different when rendered on CPU vs GPU

Support Lighting and Rendering
1

I was just playing with some particle settings and noticed that the GPU rendered the scene drastically different on than the CPU. Otherwise no changes in rendering
Is this a known bug?
CPU

cpu
cpu960×540 91.7 KB

GPU

gpu
gpu960×540 87.6 KB

2

Hi.
2.79b official release or 2.79 from buildbot/master.
If it occurs from 2.79 from buildbot/master, you should try Hybrid CPU+GPU at the same time. If you still notice differences between the tiles that CPU render and those that GPU render, it is something that you should report.

1 Like
3

That was from official. I deleted the master because of incompatibility of some add-ons. I just re downloaded it and tested it. It’s better, although not quite the same.
CPU + GPU

cpu%20only
cpu%20only960×540 119 KB

CPU only
cpu%20gpu
cpu%20gpu960×540 121 KB

GPU only
gpu%20only
gpu%20only960×540 121 KB

4

I think a reportable problem would be if you find differences between tiles taken by the CPU and those taken by the GPU in the first image using CPU+GPU at the same time. Do you find differences between those tiles in that first image?

I understand that when CPU+GPU is used, some CPU features are disabled to match GPU when volumetrics are used. But you show that GPU and CPU results are quite similar.

You could report this just in case, by sharing the .blend file and giving information about your CPU and GPU models.

5

After some more tests with volume scatter. It appears that a CPU render is much noisier than a GPU render. With some minimal visual differences. A CPU+GPU render looks identical to a GPU only render

6

So to me there are no problems here then, it is something to be expected. CPU is more capable with volumetrics and as I said earlier when CPU+GPU is used then CPU features are cropped to be able to match GPU (or something like that, I do not know exactly the technical explanation)

Edit:

Anyway, I would have expected the opposite to this :thinking: