hair sculpt collision doesn't work well with real scale human head. #115843

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opened 2023-12-06 13:58:09 +01:00 by Massimiliano Puliero · 7 comments

Massimiliano Puliero commented

2023-12-06 13:58:09 +01:00

System Information
Operating system: Windows-10-10.0.19045-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 546.17

Blender Version
Broken: version: 3.6.5, branch: blender-v3.6-release, commit date: 2023-10-16 14:30, hash: cf1e1ed46b7e

Short description of error
Collision activated in hair sculpt mode prevent to comb the hair is the model is a real scale human head.

Exact steps for others to reproduce the error

open the .blend file attached
try to comb the hair.

Thank you
Max

**System Information** Operating system: Windows-10-10.0.19045-SP0 64 Bits Graphics card: NVIDIA GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 546.17 **Blender Version** Broken: version: 3.6.5, branch: blender-v3.6-release, commit date: 2023-10-16 14:30, hash: `cf1e1ed46b7e` **Short description of error** Collision activated in hair sculpt mode prevent to comb the hair is the model is a real scale human head. <video src="/attachments/73f5ff70-a407-48c0-8db4-5c1dedf75d20" controls></video> **Exact steps for others to reproduce the error** - open the .blend file attached - try to comb the hair. Thank you Max

hair_collision.blend

3.7 MiB

hair_collisions.mp4

8.6 MiB

Massimiliano Puliero added the

labels 2023-12-06 13:58:10 +01:00

Iliya Katushenock added the

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Sculpt, Paint & Texture

labels 2023-12-06 14:50:35 +01:00

Richard Antalik added

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labels 2023-12-06 21:12:42 +01:00

Germano Cavalcante commented

2023-12-06 21:14:21 +01:00

Member

Thank you for the report.
I can confirm the issue and it will be forwarded to the developers for further inspection.

Thank you for the report. I can confirm the issue and it will be forwarded to the developers for further inspection.

Philipp Oeser commented

2023-12-07 11:23:12 +01:00

Member

Collision radius was made larger in a76b5d3a07 (think we should probably use actually used mean radius instead).

However, there is also another issue which I think is wrong: as soon as one point inside the brush radius has a collision detected, the whole curve gets reset, think there are still valid points to be moved here in such a case, will check on this...

Collision radius was made larger in a76b5d3a077e14c40a8c610fef36a5a4e2068def (think we should probably use actually used mean radius instead). However, there is also another issue which I think is wrong: as soon as one point inside the brush radius has a collision detected, the whole curve gets reset, think there are still valid points to be moved here in such a case, will check on this...

Philipp Oeser self-assigned this 2023-12-07 11:23:23 +01:00

Philipp Oeser commented

2023-12-07 14:56:00 +01:00

Member

Looked at this a bit, and the solution from e7606139ba has the problem that it keeps running into max iterations of the collision solver (and just freezes the whole curve).

There might not be a way around this (had a clumsy try at it, see below, but that probably has other issues then).

diff --git a/source/blender/geometry/intern/curve_constraints.cc b/source/blender/geometry/intern/curve_constraints.cc
index d19ce0bcfdb..991daeff56f 100644
--- a/source/blender/geometry/intern/curve_constraints.cc
+++ b/source/blender/geometry/intern/curve_constraints.cc
@@ -161,8 +161,12 @@ void solve_length_and_collision_constraints(const OffsetIndices<int> points_by_c
           else {
             /* Minimum distance is larger than allowed segment length.
              * The unilateral collision constraint is satisfied by just clamping segment length. */
+            /* For points originally inside the ray radius of the surface, this will keep
+             * iterating, eventually hitting "max_collisions" and thus revert/freeze the whole
+             * curve. Maybe better to just break here? */
             positions_cu[point_i] = prev_pos_cu + math::normalize(old_pos_su - prev_pos_cu) *
                                                       goal_segment_length_cu;
+            break;
           }
         }
         if (used_iterations == max_collisions) {

Probably the best way now would be to make the collision distance a setting (just as the old particle system had)?

Anyhow, will step down, I think @LukasTonne or @JacquesLucke better look at this

Looked at this a bit, and the solution from e7606139ba186aa4e8421a5eea277f15cfc3b358 has the problem that it keeps running into max iterations of the collision solver (and just freezes the whole curve). There might not be a way around this (had a clumsy try at it, see below, but that probably has other issues then). ```Diff diff --git a/source/blender/geometry/intern/curve_constraints.cc b/source/blender/geometry/intern/curve_constraints.cc index d19ce0bcfdb..991daeff56f 100644 --- a/source/blender/geometry/intern/curve_constraints.cc +++ b/source/blender/geometry/intern/curve_constraints.cc @@ -161,8 +161,12 @@ void solve_length_and_collision_constraints(const OffsetIndices<int> points_by_c else { /* Minimum distance is larger than allowed segment length. * The unilateral collision constraint is satisfied by just clamping segment length. */ + /* For points originally inside the ray radius of the surface, this will keep + * iterating, eventually hitting "max_collisions" and thus revert/freeze the whole + * curve. Maybe better to just break here? */ positions_cu[point_i] = prev_pos_cu + math::normalize(old_pos_su - prev_pos_cu) * goal_segment_length_cu; + break; } } if (used_iterations == max_collisions) { ``` Probably the best way now would be to make the collision distance a setting (just as the old particle system had)? ![image](/attachments/d60e614c-fc94-4ec4-862a-b8f64c767f39) Anyhow, will step down, I think @LukasTonne or @JacquesLucke better look at this

27 KiB

Philipp Oeser removed their assignment 2023-12-07 14:56:10 +01:00

Philipp Oeser added

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labels 2023-12-07 14:56:28 +01:00

sentharn commented

2024-02-16 22:47:11 +01:00

I recompiled Blender with the old radius of 0.001f and it works much better. Curve collision is useless in current form with 1:1 scale.

I don't observe any huge freezing issues. The only non-optimal behavior is that I can't really slide a hair strand sideways (tangent) easily across a surface. I have to comb it away a bit first. This is still much less annoying than not being able to use curve collision at all.

Can the distance value be made adjustable?

I recompiled Blender with the old radius of 0.001f and it works *much* better. Curve collision is useless in current form with 1:1 scale. I don't observe any huge freezing issues. The only non-optimal behavior is that I can't really slide a hair strand *sideways* (tangent) easily across a surface. I have to comb it away a bit first. This is still much less annoying than not being able to use curve collision at all. Can the distance value be made adjustable?

Jacques Lucke commented

2024-03-01 23:06:14 +01:00

Member

I'm fine with exposing the value. Just need to find a good place in the UI. Do you want to make a pull request?

It's a little bit related to the hair radius, but it seems reasonable to decouple the surface collision distance from the curve radius.

I'm fine with exposing the value. Just need to find a good place in the UI. Do you want to make a pull request? It's a little bit related to the hair radius, but it seems reasonable to decouple the surface collision distance from the curve radius.

sentharn commented

2024-03-03 06:55:34 +01:00

A PR for the UI or for the default distance? I don't have the knowledge to make a UI change. I agree though that it would be very nice to have it as a UI value. Right now it's hardcoded in the eval function for curve hair sculpting.

A PR for the UI or for the default distance? I don't have the knowledge to make a UI change. I agree though that it would be very nice to have it as a UI value. Right now it's hardcoded in the eval function for curve hair sculpting.

Jacques Lucke commented

2024-03-10 13:05:16 +01:00

Member

I meant a PR that includes the UI, but it's fine if that is a bit out of scope for you.

I meant a PR that includes the UI, but it's fine if that is a bit out of scope for you.

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