Unexpected output from Musgrave Texture #75774

New Issue

Russell · 2020-04-16T05:29:25+02:00

Russell commented

2020-04-16 05:29:25 +02:00

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.74

Blender Version
Broken: version: 2.90 (sub 0), branch: master, commit date: 2020-04-15 15:46, hash: 4dc534aa04
Worked: (newest version of Blender that worked as expected)

Short description of error
I suspect that the Fac output from the Musgrave Texture Node is outputting values less than zero. This produces unexpected results when running its output through any number of mathematical operations.

Exact steps for others to reproduce the error

Create a Musgrave Texture Node
Run its output through a Map Range node and then to the Base Color input of the Principled BSDF shader.
You must remove the Clamp checkbox on the Map Range node to see the full range of white to black that you expect. This indicates that values are outside the expected 0 to 1 range for a Fac output.

I don't know how to debug this further since we can't see the actual numerical output from any of these nodes.

What straight black produces:

What, uh, less than black produces:

Material 000.blend

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 442.74 **Blender Version** Broken: version: 2.90 (sub 0), branch: master, commit date: 2020-04-15 15:46, hash: `4dc534aa04` Worked: (newest version of Blender that worked as expected) **Short description of error** I suspect that the Fac output from the Musgrave Texture Node is outputting values less than zero. This produces unexpected results when running its output through any number of mathematical operations. **Exact steps for others to reproduce the error** 1. Create a Musgrave Texture Node 2. Run its output through a Map Range node and then to the Base Color input of the Principled BSDF shader. 3. You must remove the Clamp checkbox on the Map Range node to see the full range of white to black that you expect. This indicates that values are outside the expected 0 to 1 range for a Fac output. I don't know how to debug this further since we can't see the actual numerical output from any of these nodes. ![Screenshot (81).png](https://archive.blender.org/developer/F8476226/Screenshot__81_.png) ![Screenshot (80).png](https://archive.blender.org/developer/F8476228/Screenshot__80_.png) What straight black produces: ![Screenshot (82).png](https://archive.blender.org/developer/F8476227/Screenshot__82_.png) What, uh, less than black produces: ![Screenshot (83).png](https://archive.blender.org/developer/F8476225/Screenshot__83_.png) [Material 000.blend](https://archive.blender.org/developer/F8476233/Material_000.blend)

Russell commented

2020-04-16 05:29:25 +02:00

Added subscriber: @Russ1642

Germano Cavalcante commented

2020-04-16 16:35:00 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-04-16 16:35:00 +02:00

Changed status from 'Needs Triage' to: 'Archived'

Germano Cavalcante closed this issue

2020-04-16 16:35:00 +02:00

Germano Cavalcante self-assigned this 2020-04-16 16:35:00 +02:00

Germano Cavalcante commented

2020-04-16 16:35:00 +02:00

I can confirm that there are values less than 0 (just use the match node with Less Than mode).
Although it does not seem conventional, this is not a bug and has been working since this node was implemented.

I can confirm that there are values less than 0 (just use the match node with Less Than mode). Although it does not seem conventional, this is not a bug and has been working since this node was implemented.

Russell commented

2020-04-16 17:36:07 +02:00

Fac inputs and outputs are supposed to be limited to the range of 0 to 1. It's not 'unconventional', it breaks the workflow because it's completely unexpected. We're making assumptions about what our math will do based on the number not dropping below 0.

Tell us this please: What range of numbers does that node output? -1 to 1? -10000 to 1? -1 to 20000? We now have no idea. Are other Fac outputs not limited to the range of 0 to 1? What is the range we're supposed to expect. Seeing as Blender is moving towards a "nodes for EVERYTHING" design I'd think this is something that ought to be ironed out now.

Fac inputs and outputs are supposed to be limited to the range of 0 to 1. It's not 'unconventional', it breaks the workflow because it's completely unexpected. We're making assumptions about what our math will do based on the number not dropping below 0. Tell us this please: What range of numbers does that node output? -1 to 1? -10000 to 1? -1 to 20000? We now have no idea. Are other Fac outputs not limited to the range of 0 to 1? What is the range we're supposed to expect. Seeing as Blender is moving towards a "nodes for EVERYTHING" design I'd think this is something that ought to be ironed out now.

Germano Cavalcante commented

2020-04-16 17:46:46 +02:00

Changed status from 'Archived' to: 'Needs Triage'

Germano Cavalcante reopened this issue

2020-04-16 17:46:46 +02:00

Brecht Van Lommel commented

2020-04-16 17:47:43 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2020-04-16 17:47:43 +02:00

Changed status from 'Needs Triage' to: 'Archived'

Brecht Van Lommel closed this issue

2020-04-16 17:47:43 +02:00

Brecht Van Lommel commented

2020-04-16 17:47:43 +02:00

Ideally these would be in the range 0..1 and we may work on that in the future. But changing this is outside the scope of the bug tracker.
https://wiki.blender.org/wiki/Communication/Contact#User_Feedback_and_Requests

Ideally these would be in the range 0..1 and we may work on that in the future. But changing this is outside the scope of the bug tracker. https://wiki.blender.org/wiki/Communication/Contact#User_Feedback_and_Requests

Russell commented

2020-04-16 17:52:57 +02:00

We can't do proper math using the output from the Musgrave Texture node. For example, when you multiply two numbers together and the lowest value you're expecting is a zero, a negative number really messes things up. Which would be perfectly fine if the software wasn't LYING to you by telling you that the numbers were strictly in the 0 to 1 range. That's what "Fac" output means. That's its purpose.

Evan Wilson commented

2020-04-16 19:22:58 +02:00

Added subscriber: @EAW

Evan Wilson commented

2020-04-16 19:22:58 +02:00

Thank you for the report. You are correct. The range of the Musgrave node when set to fBM is [-1,1]. Kenton Musgrave wrote

The version of the noise function I prefer to use has zero crossings (i.e., its value is zero) at latticepoints, and a range of [-1,1]. Note at the bottom of page 3

The example in the manual shows the use of a map range node to normalize the [-1,1] range to [0,1] if that is the look you are going for.

That being said, I think you are confusing this with another issue. The reason you aren't seeing a "true black" in your 1st and 3rd images is because you are using the principled shader. The surface is reflecting the surrounding light. If you use an emission shader, or if you set the specular slider to 0, you will get results that match picture 2 and 4.

Thank you for the report. You are correct. The range of the Musgrave node when set to fBM is [-1,1]. Kenton Musgrave wrote > The version of the noise function I prefer to use has zero crossings (i.e., its value is zero) at latticepoints, and a range of [-1,1]. [Note at the bottom of page 3](https://www.classes.cs.uchicago.edu/archive/2015/fall/23700-1/final-project/MusgraveTerrain00.pdf) The [example in the manual](https://docs.blender.org/manual/en/latest/render/shader_nodes/textures/musgrave.html#examples) shows the use of a map range node to normalize the [-1,1] range to [0,1] if that is the look you are going for. That being said, I think you are confusing this with another issue. The reason you aren't seeing a "true black" in your 1st and 3rd images is because you are using the principled shader. The surface is reflecting the surrounding light. If you use an emission shader, or if you set the specular slider to 0, you will get results that match picture 2 and 4.

Russell commented

2020-04-16 19:29:02 +02:00

The issue I have isn't the range of the Musgrave Node or the shader. It's really the labelling of the Fac output. We're led to believe that ALL Fac outputs have a range of 0 to 1. Blender is moving towards having more and more nodes. If this assumption isn't correct then it should be addressed. I think it's a bad idea to have a hundred Fac outputs limited to 0-1 and then suddenly this one node is different. I was trying to do some math with the output of the node and was scratching my head trying to figure out what wasn't working. So the bug is that the output from the node is labelled Fac. Call it something else if it doesn't behave like every other Fac. Thank you.

Evan Wilson commented

2020-04-16 21:02:05 +02:00

Note: there were no other responses when I started researching and writing my above response. =)

You also have to remember why Kenton Musgrave created these noises in the first place: to create realistic procedural generated synthetic terrain models. The places where the output is less than zero are lakes.

Edit: Better render of my example

Note: there were no other responses when I started researching and writing my above response. =) You also have to remember why Kenton Musgrave created these noises in the first place: to create realistic procedural generated synthetic terrain models. The places where the output is less than zero are lakes. Edit: Better render of my example ![Lakes_v2.jpg](https://archive.blender.org/developer/F8479141/Lakes_v2.jpg)

Russell commented

2020-04-16 21:16:59 +02:00

This has NOTHING to do with the Musgrave Texture node in particular. Either Fac outputs are supposed to be in the 0 to 1 range or they're not. Blender nodes have been designed to have a common interface and that was one of the decisions. So if you want to keep the range -1 to 1 then at least call it something other than a Fac output so it's not so damn confusing. If every Fac output had a different range it'd be a mess. This is about consistency and predictability.

Evan Wilson commented

2020-04-16 21:38:25 +02:00

Again, I wrote my above comment before seeing your comment. It was an effort to describe why the range is what it is, and not intended to dismiss your point.

In #75774#911502, @Russ1642 wrote:
The issue I have isn't the range of the Musgrave Node or the shader. It's really the labelling of the Fac output. We're led to believe that ALL Fac outputs have a range of 0 to 1. Blender is moving towards having more and more nodes. If this assumption isn't correct then it should be addressed. I think it's a bad idea to have a hundred Fac outputs limited to 0-1 and then suddenly this one node is different. I was trying to do some math with the output of the node and was scratching my head trying to figure out what wasn't working. So the bug is that the output from the node is labelled Fac. Call it something else if it doesn't behave like every other Fac. Thank you.

I can get behind the output being changed from Fac to Value. But as Brecht said, that is outside the scoop of the bug tracker.

Again, I wrote my above comment before seeing your comment. It was an effort to describe why the range is what it is, and not intended to dismiss your point. > In #75774#911502, @Russ1642 wrote: > The issue I have isn't the range of the Musgrave Node or the shader. It's really the labelling of the Fac output. We're led to believe that ALL Fac outputs have a range of 0 to 1. Blender is moving towards having more and more nodes. If this assumption isn't correct then it should be addressed. I think it's a bad idea to have a hundred Fac outputs limited to 0-1 and then suddenly this one node is different. I was trying to do some math with the output of the node and was scratching my head trying to figure out what wasn't working. So the bug is that the output from the node is labelled Fac. Call it something else if it doesn't behave like every other Fac. Thank you. I can get behind the output being changed from `Fac` to `Value`. But as Brecht said, that is outside the scoop of the bug tracker.

Russell commented

2020-04-16 21:53:02 +02:00

Changing the range might be outside the scope of the bug tracker, especially since it'll break existing materials. However, the label is most certainly a bug and is easy to change.

blender-admin commented

2020-04-16 23:16:23 +02:00

This issue was referenced by c87dd76937

This issue was referenced by c87dd76937f026c4a154dc4073063959f3e5a87e

Brecht Van Lommel commented

2020-04-17 14:28:43 +02:00

Changed status from 'Archived' to: 'Resolved'

Russell commented

2020-04-18 01:11:34 +02:00

Thank you. :)

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Unexpected output from Musgrave Texture #75774