Flickering in unrelated hair strands when deleting hair #99054

New Issue

Dalai Felinto · 2022-06-21T14:46:13+02:00

Dalai Felinto commented

2022-06-21 14:46:13 +02:00

System Information
Operating system: Linux-5.13.0-48-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.73.05

Blender Version
Broken: version: 3.3.0 Alpha, branch: master, commit date: 2022-06-21 08:10, hash: ee78c860b8
Worked: n/a

Short description of error
When I delete the hair, the rest of the hair flickers. This doesn't happen when adding hair, changing their length, combing, ...

Note it also happens when deleting hair with the density brush.

Exact steps for others to reproduce the error

Open this file and delete some hair.

hair_flicker.blend

Video:

flicker-2022-06-21_14.38.51.mp4

**System Information** Operating system: Linux-5.13.0-48-generic-x86_64-with-glibc2.31 64 Bits Graphics card: NVIDIA GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 510.73.05 **Blender Version** Broken: version: 3.3.0 Alpha, branch: master, commit date: 2022-06-21 08:10, hash: `ee78c860b8` Worked: n/a **Short description of error** When I delete the hair, the rest of the hair flickers. This doesn't happen when adding hair, changing their length, combing, ... Note it also happens when deleting hair with the density brush. **Exact steps for others to reproduce the error** * Open this file and delete some hair. [hair_flicker.blend](https://archive.blender.org/developer/F13212171/hair_flicker.blend) Video: [flicker-2022-06-21_14.38.51.mp4](https://archive.blender.org/developer/F13212174/flicker-2022-06-21_14.38.51.mp4)

Dalai Felinto commented

2022-06-21 14:46:13 +02:00

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

Dalai Felinto commented

2022-06-21 14:46:13 +02:00

Added subscriber: @dfelinto

Hans Goudey commented

2022-08-03 19:37:04 +02:00

Added subscriber: @HooglyBoogly

Hans Goudey commented

2022-08-03 19:37:04 +02:00

This happens because the normals and material values are randomized by the curve index.
The proper solution would be using some sort of per-curve id attribute in the shader.
That should be optional though, because it would have a performance cost, and it wouldn't matter for sculpting outside of workbench.

The randomness could also be made optional with a shader uniform. Here's a patch for testing the affect of that: P3119: Turn of workbench curve drawing randomness

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl
index 04fef8d8b32..4bccd3a970f 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl
@@ -51,34 +51,45 @@ void main()
                               drw_view.viewinv- [x].xyz,
                               drw_view.viewinv- [x].xyz,
                               world_pos,
                               tan,
                               binor,
                               time,
                               thickness,
                               thick_time);
 
   gl_Position = point_world_to_ndc(world_pos);
+  
+  bool USE_RANDOM_NORMAL = false;
+  bool USE_RANDOM_MATERIAL = false;
 
   float hair_rand = integer_noise(hair_get_strand_id());
-  vec3 nor = workbench_hair_random_normal(tan, binor, hair_rand);
+  vec3 nor;
+  if (USE_RANDOM_NORMAL) {
+    nor = workbench_hair_random_normal(tan, binor, hair_rand);
+  }
+  else {
+    nor = workbench_hair_random_normal(tan, binor, 0.0);
+  }
 
   view_clipping_distances(world_pos);
 
   uv_interp = hair_get_customdata_vec2(au);
 
   normal_interp = normalize(normal_world_to_view(nor));
 
   workbench_material_data_get(resource_handle, color_interp, alpha_interp, _roughness, metallic);
 
   if (materialIndex == 0) {
     color_interp = hair_get_customdata_vec3(ac);
   }
 
   /* Hairs have lots of layer and can rapidly become the most prominent surface.
    * So we lower their alpha artificially. */
   alpha_interp *= 0.3;
 
-  workbench_hair_random_material(hair_rand, color_interp, _roughness, metallic);
+  if (USE_RANDOM_MATERIAL) {
+    workbench_hair_random_material(hair_rand, color_interp, _roughness, metallic);
+  }
 
   object_id = int(uint(resource_handle) & 0xFFFFu) + 1;
 }

This happens because the normals and material values are randomized by the curve index. The proper solution would be using some sort of per-curve id attribute in the shader. That should be optional though, because it would have a performance cost, and it wouldn't matter for sculpting outside of workbench. The randomness could also be made optional with a shader uniform. Here's a patch for testing the affect of that: [P3119: Turn of workbench curve drawing randomness](https://archive.blender.org/developer/P3119.txt) ```diff diff --git a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl index 04fef8d8b32..4bccd3a970f 100644 --- a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl +++ b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl @@ -51,34 +51,45 @@ void main() drw_view.viewinv- [x].xyz, drw_view.viewinv- [x].xyz, world_pos, tan, binor, time, thickness, thick_time); gl_Position = point_world_to_ndc(world_pos); + + bool USE_RANDOM_NORMAL = false; + bool USE_RANDOM_MATERIAL = false; float hair_rand = integer_noise(hair_get_strand_id()); - vec3 nor = workbench_hair_random_normal(tan, binor, hair_rand); + vec3 nor; + if (USE_RANDOM_NORMAL) { + nor = workbench_hair_random_normal(tan, binor, hair_rand); + } + else { + nor = workbench_hair_random_normal(tan, binor, 0.0); + } view_clipping_distances(world_pos); uv_interp = hair_get_customdata_vec2(au); normal_interp = normalize(normal_world_to_view(nor)); workbench_material_data_get(resource_handle, color_interp, alpha_interp, _roughness, metallic); if (materialIndex == 0) { color_interp = hair_get_customdata_vec3(ac); } /* Hairs have lots of layer and can rapidly become the most prominent surface. * So we lower their alpha artificially. */ alpha_interp *= 0.3; - workbench_hair_random_material(hair_rand, color_interp, _roughness, metallic); + if (USE_RANDOM_MATERIAL) { + workbench_hair_random_material(hair_rand, color_interp, _roughness, metallic); + } object_id = int(uint(resource_handle) & 0xFFFFu) + 1; } ```

Dalai Felinto commented

2022-08-04 13:16:50 +02:00

I had to tweak the patch to apply: P3125: Masterwork From Distant Lands

diff --git a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl
index 04fef8d8b32..3627be1e2d1 100644
--- a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl
+++ b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl
@@ -59,8 +59,18 @@ void main()
 
   gl_Position = point_world_to_ndc(world_pos);
 
+  bool USE_RANDOM_NORMAL = false;
+  bool USE_RANDOM_MATERIAL = false;
+
   float hair_rand = integer_noise(hair_get_strand_id());
-  vec3 nor = workbench_hair_random_normal(tan, binor, hair_rand);
+  vec3 nor;
+
+  if (USE_RANDOM_NORMAL) {
+    nor = workbench_hair_random_normal(tan, binor, hair_rand);
+  }
+  else {
+    nor = workbench_hair_random_normal(tan, binor, 0.0);
+  }
 
   view_clipping_distances(world_pos);
 
@@ -68,7 +78,9 @@ void main()
 
   normal_interp = normalize(normal_world_to_view(nor));
 
-  workbench_material_data_get(resource_handle, color_interp, alpha_interp, _roughness, metallic);
+  if (USE_RANDOM_MATERIAL) {
+    workbench_material_data_get(resource_handle, color_interp, alpha_interp, _roughness, metallic);
+  }
 
   if (materialIndex == 0) {
     color_interp = hair_get_customdata_vec3(ac);

I had to tweak the patch to apply: [P3125: Masterwork From Distant Lands](https://archive.blender.org/developer/P3125.txt) ``` diff --git a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl index 04fef8d8b32..3627be1e2d1 100644 --- a/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl +++ b/source/blender/draw/engines/workbench/shaders/workbench_prepass_hair_vert.glsl @@ -59,8 +59,18 @@ void main() gl_Position = point_world_to_ndc(world_pos); + bool USE_RANDOM_NORMAL = false; + bool USE_RANDOM_MATERIAL = false; + float hair_rand = integer_noise(hair_get_strand_id()); - vec3 nor = workbench_hair_random_normal(tan, binor, hair_rand); + vec3 nor; + + if (USE_RANDOM_NORMAL) { + nor = workbench_hair_random_normal(tan, binor, hair_rand); + } + else { + nor = workbench_hair_random_normal(tan, binor, 0.0); + } view_clipping_distances(world_pos); @@ -68,7 +78,9 @@ void main() normal_interp = normalize(normal_world_to_view(nor)); - workbench_material_data_get(resource_handle, color_interp, alpha_interp, _roughness, metallic); + if (USE_RANDOM_MATERIAL) { + workbench_material_data_get(resource_handle, color_interp, alpha_interp, _roughness, metallic); + } if (materialIndex == 0) { color_interp = hair_get_customdata_vec3(ac); ```

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Flickering in unrelated hair strands when deleting hair #99054