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Path-CPU vs Path-GPU

Posted: Sat Feb 23, 2019 5:00 am
by 29A
Hi !
I'm a newbie in Lux, and wonder why is there so big difference between Path CPU and Path OpenCL rendering ?
The GPU one has a lot of reflections of the top light
Path+CPU.png
Path+CPU.png (33.42 KiB) Viewed 1080 times
Path+GPU.png
Path+GPU.png (42.03 KiB) Viewed 1080 times
Compare, Bdir
BiDir.png
BiDir.png (30.84 KiB) Viewed 1080 times
And with another, there are some lines appeared ???
Path-CPU-RT.png
Path-CPU-RT.png (42.76 KiB) Viewed 1080 times
Path-GPU-RT.png
Path-GPU-RT.png (44.16 KiB) Viewed 1080 times
I'm using Blender 2.79b, with LuxCore 2.1
On Windows 10 Pro, i5-4460S, 16Gb RAM and NVIDIA GeForce GTX 1060 3Gb

Here are the scenes
https://1drv.ms/u/s!AgbVw9eIy-h-hatVu7O6jSxKruOwoA
https://1drv.ms/u/s!AgbVw9eIy-h-hatYXeJce1UMcDuHow

The last scene won't render correctly without this displace map https://1drv.ms/u/s!AgbVw9eIy-h-hataSTYGut0LyBVqxQ, unpack it to the same level as blend file. Blender cannot pack textures which consist of multiple files :cry:

Re: Path-CPU vs Path-GPU

Posted: Sat Feb 23, 2019 10:22 am
by Sharlybg
Try to update your Gpu driver to the last nvidia driver.

Re: Path-CPU vs Path-GPU

Posted: Sat Feb 23, 2019 3:11 pm
by 29A
You will be laughing, but after update the things got worse.
Just installed a day old (02/22/2019) NVIDIA drivers version 419.17.
Path-CPU (took 00:02:48)
Path-CPU-new version.png
Path-CPU-new version.png (42.81 KiB) Viewed 1049 times
Path-GPU (took 00:00:35)
Path-GPU-new version.png
Path-GPU-new version.png (49.42 KiB) Viewed 1049 times
And just to be sure, tried it on Azure VM, Windows 10 Pro, with 6 Core Xeon E5-2690, and 56Gb of RAM, NVIDIA Tesla M60, with latest GRID Drivers (412.16), you know what ? It does the same but a bit faster (00:00:30) and with the same incorrect results
azure-tesla-M60.png
azure-tesla-M60.png (44.22 KiB) Viewed 1049 times
P.S. if anyone interested, for CPU it was 00:01:28

Re: Path-CPU vs Path-GPU

Posted: Sat Feb 23, 2019 3:41 pm
by Dade
29A wrote:
Sat Feb 23, 2019 5:00 am
The GPU one has a lot of reflections of the top light
Uh, I can replicated the problem on my (AMD) GPU so it is not driver related. I will check what is going on.

Re: Path-CPU vs Path-GPU

Posted: Sat Feb 23, 2019 8:21 pm
by 29A
Dade wrote:
Sat Feb 23, 2019 3:41 pm
29A wrote:
Sat Feb 23, 2019 5:00 am
The GPU one has a lot of reflections of the top light
Uh, I can replicated the problem on my (AMD) GPU so it is not driver related. I will check what is going on.
Actually both scenes are not important for me, accept it as a bug report.

Re: Path-CPU vs Path-GPU

Posted: Sun Feb 24, 2019 4:34 pm
by Sharlybg
You will be laughing
Sorry but i do :lol:

Re: Path-CPU vs Path-GPU

Posted: Mon Feb 25, 2019 9:01 am
by lacilaci
I also noticed some weird noise difference with glass material.
Looks almost as if the gpu noise/samples are smeared horizontaly.
cpu:
cpunoise.jpg
gpu:
gpunoise.jpg

Re: Path-CPU vs Path-GPU

Posted: Mon Feb 25, 2019 11:19 am
by Dade
Dade wrote:
Sat Feb 23, 2019 3:41 pm
Uh, I can replicated the problem on my (AMD) GPU so it is not driver related. I will check what is going on.
The problem is in the scene: there are 2 coincident "Area" and "Area.001" objects. They are 2 area lamps and "Area" has a gain set to 0.0. Just delete "Area" and CPU and GPU will produce the same rendering. Assume the duplicates are a mistake from some past editing.

Having 2 coincide objects will produce an unknown result as rays will hit one or the other based on numerical errors.

I have downloaded the second scene however you may have posted the wrong one (.blend1 extension ?), it doesn't seem to produce the rendering you posted :?:

Re: Path-CPU vs Path-GPU

Posted: Tue Feb 26, 2019 7:39 am
by 29A
Dade wrote:
Mon Feb 25, 2019 11:19 am
Dade wrote:
Sat Feb 23, 2019 3:41 pm
Uh, I can replicated the problem on my (AMD) GPU so it is not driver related. I will check what is going on.
The problem is in the scene: there are 2 coincident "Area" and "Area.001" objects. They are 2 area lamps and "Area" has a gain set to 0.0. Just delete "Area" and CPU and GPU will produce the same rendering. Assume the duplicates are a mistake from some past editing.

Having 2 coincide objects will produce an unknown result as rays will hit one or the other based on numerical errors.

I have downloaded the second scene however you may have posted the wrong one (.blend1 extension ?), it doesn't seem to produce the rendering you posted :?:
I see the problem with 2 areas, cannot check it right now, but i'm sure this is the reason, thank you !
2nd file is wrong, this is good one, https://1drv.ms/u/s!AgbVw9eIy-h-hatZ024Uxkt4jR_LpQ but you also need to unzip this display map https://1drv.ms/u/s!AgbVw9eIy-h-hataSTYGut0LyBVqxQ to the same folder. There are also 2 objects on the same place, but with animation first one (plane) is hided by scale and plane.001 is shown on 30th frame

Re: Path-CPU vs Path-GPU

Posted: Wed Feb 27, 2019 12:17 pm
by Dade
29A wrote:
Tue Feb 26, 2019 7:39 am
2nd file is wrong, this is good one, https://1drv.ms/u/s!AgbVw9eIy-h-hatZ024Uxkt4jR_LpQ but you also need to unzip this display map https://1drv.ms/u/s!AgbVw9eIy-h-hataSTYGut0LyBVqxQ to the same folder. There are also 2 objects on the same place, but with animation first one (plane) is hided by scale and plane.001 is shown on 30th frame
The source of the problem is in the tessellation of the cube, it is made of half million of triangles:

cube.jpg

and the way it is done is quite terrible for numerical precision, a lot of tiny long triangles. I don't know how Blender works but you should fix the object tessellation in order to not have hundred of thousand of useless triangles (most of them can just be replaced with a single triangle). I assume you can apply some kind of object simplification modifier.

The fact that LuxCore on GPU has a reduced precision compared to LuxCore on CPU is known problem but with that kind of tessellation, you are going to have problems on CPU too, first or later.