Multires: The "Simple" subdivision type is not working as it should (it's still smoothing the mesh) #74869

New Issue

TheRedWaxPolice · 2020-03-18T04:07:06+01:00

TheRedWaxPolice commented

2020-03-18 04:07:06 +01:00

System Information
Win 10

Blender Version
Broken: blender-2.83-dc2df8307f41-windows64
Worked: Before the recent multires fixes?

Short description of error
The "Simple" subdivision type is not working as it should, It starts smoothing the mesh after the second subdivision level
Also if you switch back to Catmull-Clark after the steps below, the mesh will be weirdly deformed

Exact steps for others to reproduce the error
Launch Blender
Add a Multires mod to the cube
Switch to Simple mode
Click Subdivide once (okay)
Click Subdivide again (now it starts smoothing the mesh)
(Now you can switch back to Catmull-Clark type to see the deformed mesh)

See:

2020-03-18_03-30-48.mp4

**System Information** Win 10 **Blender Version** Broken: blender-2.83-dc2df8307f41-windows64 Worked: Before the recent multires fixes? **Short description of error** The "Simple" subdivision type is not working as it should, It starts smoothing the mesh after the second subdivision level **Also** if you switch back to Catmull-Clark after the steps below, the mesh will be weirdly deformed **Exact steps for others to reproduce the error** Launch Blender Add a Multires mod to the cube Switch to Simple mode Click Subdivide once (okay) Click Subdivide again (now it starts smoothing the mesh) (Now you can switch back to Catmull-Clark type to see the deformed mesh) **See:** [2020-03-18_03-30-48.mp4](https://archive.blender.org/developer/F8413164/2020-03-18_03-30-48.mp4)

TheRedWaxPolice commented

2020-03-18 04:07:06 +01:00

Added subscriber: @TheRedWaxPolice

Philipp Oeser commented

2020-03-18 10:34:12 +01:00

Added subscribers: @Sergey, @lichtwerk

Philipp Oeser commented

2020-03-18 10:34:12 +01:00

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

Philipp Oeser commented

2020-03-18 10:34:12 +01:00

Can confirm.

CC @Sergey

Can confirm. CC @Sergey

Brecht Van Lommel commented

2020-03-18 19:12:51 +01:00

Added subscriber: @brecht

Brecht Van Lommel commented

2020-03-18 19:12:51 +01:00

@Sergey, can we just remove simple mode? There's not really any hope of smooth propagation with simple subdivision, better not to support it at all.

Sergey Sharybin commented

2020-03-18 20:28:05 +01:00

@brecht, this is something what i am not sure about, and not sure about best timeline.

For the Subdivision Surface modifier it will make sense to move Simple from being a modifier option to a separate modifier. Will make Subdivision Modifier code smaller and easier (since it will be limited to Catmull-Clark only), and will bring more efficient Simple Subdivisions functionality.

For the multires I am not so sure. On the one hand having Simple options is very tricky: starting from technical aspects of tangent space not being continuous, and the going into topics like what's supposed to happen when you toggle Simple/Catmull-Clark. So having Simple option removed seems to have single rock-solid workflow.

On another hand, there might be some very good usecase (which I personally am not aware of) for being able to do simple subdivisions on multires. And technically it should be possible to propagate things in a bilinear fashion (which kind of fits overall behavior of the modifier, and, hopefully can be a simple tweak in the propagation code without causing propagation artifacts).

I am all fine for removing this obscure option because it just causes mathematical hell, but I don't really want to remove whole class of workflows because of that. Do you remember why this was added as an option in the first place?

@brecht, this is something what i am not sure about, and not sure about best timeline. For the Subdivision Surface modifier it will make sense to move Simple from being a modifier option to a separate modifier. Will make Subdivision Modifier code smaller and easier (since it will be limited to Catmull-Clark only), and will bring more efficient Simple Subdivisions functionality. For the multires I am not so sure. On the one hand having Simple options is very tricky: starting from technical aspects of tangent space not being continuous, and the going into topics like what's supposed to happen when you toggle Simple/Catmull-Clark. So having Simple option removed seems to have single rock-solid workflow. On another hand, there might be some very good usecase (which I personally am not aware of) for being able to do simple subdivisions on multires. And technically it should be possible to propagate things in a bilinear fashion (which kind of fits overall behavior of the modifier, and, hopefully can be a simple tweak in the propagation code without causing propagation artifacts). I am all fine for removing this obscure option because it just causes mathematical hell, but I don't really want to remove whole class of workflows because of that. Do you remember why this was added as an option in the first place?

Brecht Van Lommel commented

2020-03-18 20:42:50 +01:00

As far as I know it only exists is because it was copied over from the subsurf modifier with all the other settings. Of course someone might have found a use for it afterwards.

Even if it's possible to make it work, I think the goal for 2.83 should be to make the basics of multires work well. I would rather time be spent on making the basic use case for multires work well than worrying about every possible use case.

As far as I know it only exists is because it was copied over from the subsurf modifier with all the other settings. Of course someone might have found a use for it afterwards. Even if it's possible to make it work, I think the goal for 2.83 should be to make the basics of multires work well. I would rather time be spent on making the basic use case for multires work well than worrying about every possible use case.

TheRedWaxPolice commented

2020-03-18 23:53:39 +01:00

@Sergey @brecht
The "Simple" mode (sometimes called Flat) is actually something that exists in the "multires" system of other applications, and it's mostly used to subdivide a base mesh without lose volume, before going to the "smooth" (Catmull-Clark) mode.
The difference in Blender is that,, both modes (Catmull-Clark/Simple) they don't work together, we can only either use Catmull-Clark or Simple, while in other apps they kinda work together.

For example, let's say you add the Multires to the cube, switch to Simple mode and subdivide 4 times. You should get this result:

Now if you switch to Catmull-Clark, this is what should happen (nothing should happen)

Yeah, as you can see above, nothing should happen when you switch modes.

Things only happen when you start subdividing.. So if you hit subdivide now in Catmull-Clark mode, this is what should happen:

As you can see, the smoothing starts happening based on what's already there (in this case the subdivisions generated by the Simple mode). This is how it works on apps like Zbrush etc... There's no actually switching modes.. The two types of subdivisions are kinda applied on top of each other when you subdivide, if that makes sense..

I hope you understand my crappy english... 🙂

@Sergey @brecht The "Simple" mode *(sometimes called Flat)* is actually something that exists in the "multires" system of other applications, and it's mostly used to subdivide a base mesh without lose volume, before going to the "smooth" (Catmull-Clark) mode. The difference in Blender is that,, both modes (Catmull-Clark/Simple) they don't work together, we can only either use Catmull-Clark or Simple, while in other apps they kinda work together. For example, let's say you add the Multires to the cube, switch to Simple mode and subdivide 4 times. You should get this result: ![image.png](https://archive.blender.org/developer/F8414581/image.png) Now if you switch to Catmull-Clark, this is what should happen **(nothing should happen)** ![image.png](https://archive.blender.org/developer/F8414588/image.png) Yeah, as you can see above, nothing should happen when you switch modes. Things only happen when you start subdividing.. So if you hit subdivide now in Catmull-Clark mode, this is what should happen: ![image.png](https://archive.blender.org/developer/F8414600/image.png) As you can see, the smoothing starts happening based on what's already there *(in this case the subdivisions generated by the Simple mode)*. This is how it works on apps like Zbrush etc... There's no actually switching modes.. The two types of subdivisions are kinda applied on top of each other when you subdivide, if that makes sense.. *I hope you understand my crappy english...* 🙂

Brecht Van Lommel commented

2020-03-19 00:10:00 +01:00

That seems pretty similar to subdividing in edit mode or using creases, it's not clear to me this use case require a simple subdivision mode.

This is actually how creases are mathematically defined: there are crease values that correspond to applying N linear subdivisions followed by smooth subdivisions. It's just that with creases you are also able to get values between N and N+1.

That seems pretty similar to subdividing in edit mode or using creases, it's not clear to me this use case require a simple subdivision mode. This is actually how creases are mathematically defined: there are crease values that correspond to applying N linear subdivisions followed by smooth subdivisions. It's just that with creases you are also able to get values between N and N+1.

Pablo Dobarro commented

2020-03-19 00:25:34 +01:00

Added subscriber: @PabloDobarro

Pablo Dobarro commented

2020-03-19 00:25:34 +01:00

If we want to support that kind of workflow from the modifier, this should be a "subdivide simple" operator instead of a mode of the modifier. Then, when using this option, the next subdivision level coordinates will be initialized to the subdivide simple positions when creating that level, but propagation will continue working as usual.
On the other hand, we can simple remove it. It is possible to do the same thing by unsubdividing from multires (which is planned) after subdividing the mesh in edit mode or with a regular subdiv modifier in simple mode.

If we want to support that kind of workflow from the modifier, this should be a "subdivide simple" operator instead of a mode of the modifier. Then, when using this option, the next subdivision level coordinates will be initialized to the subdivide simple positions when creating that level, but propagation will continue working as usual. On the other hand, we can simple remove it. It is possible to do the same thing by unsubdividing from multires (which is planned) after subdividing the mesh in edit mode or with a regular subdiv modifier in simple mode.

Nelson commented

2020-03-19 05:27:40 +01:00

Added subscriber: @NelsonNAS

Nelson commented

2020-03-19 05:27:40 +01:00

In #74869#893952, @PabloDobarro wrote:
It is possible to do the same thing by unsubdividing from multires (which is planned) after subdividing the mesh in edit mode or with a regular subdiv modifier in simple mode.

This sounds like a very convoluted workflow imo.
I'd very much prefer to have it working as TheRedWaxPolice described which is in line with your first suggestion. (zbrush style)
The convenience and comfort of having it working like that would be just amazing.

> In #74869#893952, @PabloDobarro wrote: > It is possible to do the same thing by unsubdividing from multires (which is planned) after subdividing the mesh in edit mode or with a regular subdiv modifier in simple mode. This sounds like a very convoluted workflow imo. I'd very much prefer to have it working as TheRedWaxPolice described which is in line with your first suggestion. (zbrush style) The convenience and comfort of having it working like that would be just amazing.

blender-admin commented

2020-03-19 11:56:35 +01:00

This issue was referenced by 885caa4535

This issue was referenced by 885caa4535850f655454edf746c72ab87f5dcc21

Sergey Sharybin commented

2020-03-19 12:03:13 +01:00

Changed status from 'Confirmed' to: 'Resolved'

Sergey Sharybin closed this issue

2020-03-19 12:03:13 +01:00

Sergey Sharybin self-assigned this 2020-03-19 12:03:13 +01:00

Debuk commented

2020-03-20 09:24:23 +01:00