Hair cards with alpha texture map produce weird black color under cycles. #96816

New Issue

NXSK · 2022-03-27T15:39:29+02:00

NXSK commented

2022-03-27 15:39:29 +02:00

System Information
Operating system: windows 10
Graphics card: RTX 3090

Blender Version
Broken: 3.1 stable

transparency issue.blend
It looks like the transparency ray depth doesn't calculate the opaque object between transparent ones. Even I raised the transparency light path up to 50, it still shows some black shadows of the hair cards.

With blender 3.0, it works correctly. Even just 8 of transparency depth.
With 12 of transparency depth, the black issue almost gone.

It has 2 copies of hair cards overlaping each other. One of it's normal faces outside, another one faces inside.

**System Information** Operating system: windows 10 Graphics card: RTX 3090 **Blender Version** Broken: 3.1 stable ![Transparency issue.jpg](https://archive.blender.org/developer/F12949881/Transparency_issue.jpg) ![Transparency issue 1.jpg](https://archive.blender.org/developer/F12949884/Transparency_issue_1.jpg) [transparency issue.blend](https://archive.blender.org/developer/F12949899/transparency_issue.blend) It looks like the transparency ray depth doesn't calculate the opaque object between transparent ones. Even I raised the transparency light path up to 50, it still shows some black shadows of the hair cards. ![3.0.jpg](https://archive.blender.org/developer/F12949965/3.0.jpg) ![3.0 12.jpg](https://archive.blender.org/developer/F12949976/3.0_12.jpg) With blender 3.0, it works correctly. Even just 8 of transparency depth. With 12 of transparency depth, the black issue almost gone. It has 2 copies of hair cards overlaping each other. One of it's normal faces outside, another one faces inside.

NXSK commented

2022-03-27 15:39:29 +02:00

Added subscriber: @NXSK

Riccardo Fasoli commented

2022-03-27 18:15:37 +02:00

Added subscriber: @fasoric.vj

Riccardo Fasoli commented

2022-03-27 18:15:37 +02:00

i'm noticing this problem too.
are those planes overlapping?

quoting from the 3.1 release notes :

"Ray Tracing Precision
Many artifacts from rendering small, large and far away objects have been eliminated. There will always be object scales where numerical precision becomes a problem, but it's further out now.

There can still be artifacts with rendering overlapping geometry, in some cases more severe than before. Such overlapping geometry should be removed, or have a small distance added in between."

i'm noticing this problem too. are those planes overlapping? quoting from the 3.1 [release notes ](https://wiki.blender.org/wiki/Reference/Release_Notes/3.1/Cycles): "Ray Tracing Precision Many artifacts from rendering small, large and far away objects have been eliminated. There will always be object scales where numerical precision becomes a problem, but it's further out now. There can still be artifacts with rendering overlapping geometry, in some cases more severe than before. Such overlapping geometry should be removed, or have a small distance added in between."

NXSK commented

2022-03-28 03:39:47 +02:00

@fasoric.vj Yes, the hair planes have 2 copies overlapping. And one of them the normal is flipped.
This is a game model. I think using this geometry hair technique is to achive the effect that the hair is perfect from most of the angle of the view.
I'm not sure if it will be a problem that geometry hair has intersection.

But I found the transparency depth calculation a bit confusing. As the project file I uploaded, there are 22 planes and a cube at middle. 10 of the planes stays between the camrea and the cube. If my understanding is correct, I need 10 transparency depth to avoid black issues. But the truth is 10 transparency depth is not enough. It still shows black shadows from the planes inside the cube.

And another question: Is there a plan that introduce a technique just like sprite in Redshift that has no limitation of the transparency depth. It can be used at leaves and geometry hair.

@fasoric.vj Yes, the hair planes have 2 copies overlapping. And one of them the normal is flipped. This is a game model. I think using this geometry hair technique is to achive the effect that the hair is perfect from most of the angle of the view. I'm not sure if it will be a problem that geometry hair has intersection. But I found the transparency depth calculation a bit confusing. As the project file I uploaded, there are 22 planes and a cube at middle. 10 of the planes stays between the camrea and the cube. If my understanding is correct, I need 10 transparency depth to avoid black issues. But the truth is 10 transparency depth is not enough. It still shows black shadows from the planes inside the cube. And another question: Is there a plan that introduce a technique just like sprite in Redshift that has no limitation of the transparency depth. It can be used at leaves and geometry hair.

Philipp Oeser commented

2022-03-28 13:10:31 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2022-03-28 13:10:31 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Philipp Oeser commented

2022-03-28 13:10:31 +02:00

Hm, so this is what I am seeing:
3.2 e2e4c1daaa
{F12952247 size=full}
3.1 release
{F12952256 size=full}
3.0 release
{F12952251 size=full}

Just to make sure (because your screenshots dont match the file that is provided):

these are the "artifacts" we are talking about, right?

With blender 3.0, it works correctly. Even just 8 of transparency depth.

Does this mean you are not seeing the "shadow squares" in 3.0 at all?

Hm, so this is what I am seeing: 3.2 e2e4c1daaa {[F12952247](https://archive.blender.org/developer/F12952247/image.png) size=full} 3.1 release {[F12952256](https://archive.blender.org/developer/F12952256/image.png) size=full} 3.0 release {[F12952251](https://archive.blender.org/developer/F12952251/image.png) size=full} Just to make sure (because your screenshots dont match the file that is provided): - these are the "artifacts" we are talking about, right? > With blender 3.0, it works correctly. Even just 8 of transparency depth. Does this mean you are not seeing the "shadow squares" in 3.0 at all?

NXSK commented

2022-03-28 16:23:58 +02:00

@lichtwerk Sorry, that's my misjudgement. I think maybe the reason that causes the geometry hair showing black artifacts is the algorithm of transparency depth. But I still don't understand why I need 15 or more ray depth to clear the artifacts even there are only 10 layers of transparent object.

Philipp Oeser commented

2022-03-29 11:46:57 +02:00

Changed status from 'Needs User Info' to: 'Needs Developer To Reproduce'

Philipp Oeser commented

2022-03-29 11:46:57 +02:00

Added subscribers: @ThomasDinges, @brecht

Philipp Oeser commented

2022-03-29 11:46:57 +02:00

In #96816#1331044, @NXSK wrote:
@lichtwerk Sorry, that's my misjudgement. I think maybe the reason that causes the geometry hair showing black artifacts is the algorithm of transparency depth. But I still don't understand why I need 15 or more ray depth to clear the artifacts even there are only 10 layers of transparent object.

Without digging deeper, I am unsure as well.
Could it be, that we spend 10 transparent bounces already on the way to the cube, and then for the shadow rays we need the additional ones?
But would this explain why these look so blocky? And why they look so different between versions? (they even used to look different on CPU/GPU, but that was unified somewhere along the way...)
Maybe @ThomasDinges or @brecht would know right away

> In #96816#1331044, @NXSK wrote: > @lichtwerk Sorry, that's my misjudgement. I think maybe the reason that causes the geometry hair showing black artifacts is the algorithm of transparency depth. But I still don't understand why I need 15 or more ray depth to clear the artifacts even there are only 10 layers of transparent object. Without digging deeper, I am unsure as well. Could it be, that we spend 10 transparent bounces already on the way to the cube, and then for the shadow rays we need the additional ones? But would this explain why these look so blocky? And why they look so different between versions? (they even used to look different on CPU/GPU, but that was unified somewhere along the way...) Maybe @ThomasDinges or @brecht would know right away

Mustard commented

2022-04-21 13:33:12 +02:00

Added subscriber: @Mustard

Brecht Van Lommel commented

2022-07-15 18:55:31 +02:00

Changed status from 'Needs Developer To Reproduce' to: 'Archived'

Brecht Van Lommel closed this issue

2022-07-15 18:55:31 +02:00

Brecht Van Lommel commented

2022-07-15 18:55:31 +02:00

@lichtwerk is correct, indirect and shadows require additional transparency bounces. The blocky look comes from the stacked planes, those corners are the corners of the planes.

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Hair cards with alpha texture map produce weird black color under cycles. #96816