Displacement on GPU very different/jagged

[kosso_olli]

I have some problems with displacement on the GPU. First of all, landscape mode is not supported, right? Switching to 3D doens't really help, because no matter how I set up the displacement in the modifiert, it always looks jagged. Reducing the edge length and subdivision only increases the time needed at the start of the rendering, but the output looks the same. In RT CPU everything looks fine.

Regards

Oliver

[tashko.zashev]

Hi,

Could you please post some render examples or the scene file ?
Have you made any changes to the Filter Blur parameter ?

[kosso_olli]

Dear Tashko,
will post the scene file on Monday. As far as I remember I did not make any changes to the filter parameters. I used the Vray HDRI loader for the displacement map with elliptical filtering.

[kosso_olli]

The link to the scene file and this thread was sent to the support team.

[Svetlozar Draganov]

The result generated by the GPU is different because the GPU texture re-sizing is active and the Texture Format is set to 8-bit while the texture used for displacement is actually 16-bit.



Set the GPU Textures to Full Size and Texture Format to 16-bit(Half) and the result will be closer to the CPU one.

[kosso_olli]

Doesn't work here. Left is CPU, right is GPU. No change in settings, except for texture size and format (half).

[vlado]

I guess it's better to post a scene for this. Reducing the edge length works fine for me in general (whereas the resizing of textures on the GPU has no effect, since the displacement is done on the CPU anyways).

Best regards,
Vlado

[kosso_olli]

I already sent the scene to the support. The strange thing is that I have set the edge length to look good in Vray Adv and RT CPU, but for some reason it looks totally odd on the GPU.

[Svetlozar Draganov]

Doesn't work here. Left is CPU, right is GPU. No change in settings, except for texture size and format (half).

Please excuse me, I have misled by the RGB channel which looked much better when the texture is not resized but the normals-channel is indeed the same.
It seems that there is something wrong with Edge Length parameter since it generates less detailed mesh when rendering on the GPU.
I just added a note about that into our bug-tracking system and I'll let you know when we have some progress on that matter.

Meanwhile you could increase the quality of the displacement by decreasing Edge Length value to 1 - this value generates almost identical result on both CPU and GPU.

[kosso_olli]

How much time did the preparation take for this on your machine? When setting the edge length to 1, I had to wait very long and cancelled the process after 3min of waiting.

[Svetlozar Draganov]

It was no different from edge length = 4 or at least I didn't notice any slowdown at all.
There might be something with the GPU memory involved, how much GPU memory do you have?
The GPU I used for the test have 6GB of RAM.

[Svetlozar Draganov]

I've run run another test and indeed there is a small difference in the time between a value of 4 and 1 but it is about 10 seconds.

[kosso_olli]

6GB of video ram here, too. Will test some more.

[Svetlozar Draganov]

Can you also try with a value in between 4 and 1, let's start with 3 and if worked fine try with 2.