(Hair)Curl Kink Flatness Setting Not Working #77925

New Issue

Michael Berhanu · 2020-06-16T19:00:38+02:00

Michael Berhanu commented

2020-06-16 19:00:38 +02:00

System Information
Operating system: Windows-10-10.0.17763-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87

Blender Version
Broken: version: 2.83.0, branch: master, commit date: 2020-06-03 14:38, hash: 211b6c29f7
Last Worked: 2.69.0 r60995 (from 2013)

Curl Kink Flatness Setting not working as expected

The purpose of Flatness setting is to give the particles a ribbon-like flatness when "kinking" particularly in the “Curl” option.
For comparison the "Wave” option works as expected
This bug however collapses the children strands to the guide/parent hair.
I only found this to work on an older Blender 2.69.0, it doesn't work as expected on 2.83 LTS or even Stable 2.79

Exact steps for others to reproduce the error

Use "Simple" mode of Children setting for strand hair
Turn on "Curl" kink option
Set the Flatness value to 1 for clearly seeing what happens
Switching between “Curl” and “Wave” modes shows issue

Opening the file attached on 2.69 will show how it’s supposed to look. As opposed to 2.83 LTS.
Attached Screenshots should also help.

Blend file: Curl_Kink_Flatness_Setting.blend
Screenshots:

Thank you!

Michael

**System Information** Operating system: Windows-10-10.0.17763-SP0 64 Bits Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87 **Blender Version** Broken: version: 2.83.0, branch: master, commit date: 2020-06-03 14:38, hash: `211b6c29f7` Last Worked: 2.69.0 r60995 (from 2013) **Curl Kink Flatness Setting not working as expected** - The purpose of Flatness setting is to give the particles a ribbon-like flatness when "kinking" particularly in the “Curl” option. - For comparison the "Wave” option works as expected - This bug however collapses the children strands to the guide/parent hair. - I only found this to work on an older Blender 2.69.0, it doesn't work as expected on 2.83 LTS or even Stable 2.79 **Exact steps for others to reproduce the error** 1. Use "Simple" mode of Children setting for strand hair 2. Turn on "Curl" kink option 3. Set the Flatness value to 1 for clearly seeing what happens 4. Switching between “Curl” and “Wave” modes shows issue Opening the file attached on 2.69 will show how it’s supposed to look. As opposed to 2.83 LTS. Attached Screenshots should also help. Blend file: [Curl_Kink_Flatness_Setting.blend](https://archive.blender.org/developer/F8625729/Curl_Kink_Flatness_Setting.blend) Screenshots: ![1.png](https://archive.blender.org/developer/F8625737/1.png) ![2.png](https://archive.blender.org/developer/F8625741/2.png) ![3.png](https://archive.blender.org/developer/F8625748/3.png) Thank you! - Michael

Michael Berhanu commented

2020-06-16 19:00:39 +02:00

Added subscriber: @MichaelBerhanu

Germano Cavalcante commented

2020-06-17 21:40:44 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-06-17 21:40:44 +02:00

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

Germano Cavalcante commented

2020-06-17 21:40:44 +02:00

This option is currently undoing the radius effect, which in fact does not make much sense.

Germano Cavalcante commented

2020-06-17 22:00:53 +02:00

Problem introduced by acf45062

Problem introduced by acf45062

Germano Cavalcante commented

2020-06-18 03:44:49 +02:00

Added subscriber: @LukasTonne

Germano Cavalcante commented

2020-06-18 03:44:49 +02:00

I thought about this problem and found a solution that may be the middle ground between what was solved in acf45062 and the problem described in that report.
The idea is not to flatness in the direction of the strand, so other properties like the radius rougness for the child strands can be used to have a similar result:

diff --git a/source/blender/blenkernel/intern/particle_child.c b/source/blender/blenkernel/intern/particle_child.c
index dcd2a0b8fae..1c2ec847949 100644
--- a/source/blender/blenkernel/intern/particle_child.c
+++ b/source/blender/blenkernel/intern/particle_child.c
@@ -483,8 +483,13 @@ void do_kink(ParticleKey *state,
       axis_angle_to_quat(q1, par_vel, t);
       mul_qt_v3(q1, curl_offset);
 
-      interp_v3_v3v3(par_vec, state->co, par_co, flat);
-      add_v3_v3v3(result, par_vec, curl_offset);
+      if (flat > 0.f) {
+        float proj[3];
+        project_v3_v3v3(proj, par_vec, par_vel);
+        sub_v3_v3(proj, par_vec);
+        madd_v3_v3fl(curl_offset, proj, -flat);
+      }
+      add_v3_v3v3(result, state->co, curl_offset);
       break;
     }
     case PART_KINK_RADIAL: {

@LukasTonne, can you take a look?

I thought about this problem and found a solution that may be the middle ground between what was solved in acf45062 and the problem described in that report. The idea is not to flatness in the direction of the strand, so other properties like the radius rougness for the child strands can be used to have a similar result: ``` diff --git a/source/blender/blenkernel/intern/particle_child.c b/source/blender/blenkernel/intern/particle_child.c index dcd2a0b8fae..1c2ec847949 100644 --- a/source/blender/blenkernel/intern/particle_child.c +++ b/source/blender/blenkernel/intern/particle_child.c @@ -483,8 +483,13 @@ void do_kink(ParticleKey *state, axis_angle_to_quat(q1, par_vel, t); mul_qt_v3(q1, curl_offset); - interp_v3_v3v3(par_vec, state->co, par_co, flat); - add_v3_v3v3(result, par_vec, curl_offset); + if (flat > 0.f) { + float proj[3]; + project_v3_v3v3(proj, par_vec, par_vel); + sub_v3_v3(proj, par_vec); + madd_v3_v3fl(curl_offset, proj, -flat); + } + add_v3_v3v3(result, state->co, curl_offset); break; } case PART_KINK_RADIAL: { ``` @LukasTonne, can you take a look?

Philipp Oeser removed the

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(Hair)Curl Kink Flatness Setting Not Working #77925