Hair Info Length Attribute

Goal is to add the length attribute to the Hair Info node, for better control over color gradients or similar along the hair.

Reviewed By: #eevee_viewport, brecht

Differential Revision: https://developer.blender.org/D10481

17 files changed, 182 insertions, 63 deletions

diff --git a/source/blender/blenkernel/intern/customdata.c b/source/blender/blenkernel/intern/customdata.c
index ad2d5d267d5..3bb02e1856b 100644
--- a/source/blender/blenkernel/intern/customdata.c
+++ b/source/blender/blenkernel/intern/customdata.c
@@ -1856,6 +1856,8 @@ static const LayerTypeInfo LAYERTYPEINFO[CD_NUMTYPES] = {
      NULL,
      NULL,
      NULL},
+    /* 51: CD_HAIRLENGTH */
+    {sizeof(float), "float", 1, NULL, NULL, NULL, NULL, NULL, NULL},
 };
 
 static const char *LAYERTYPENAMES[CD_NUMTYPES] = {
@@ -1912,6 +1914,7 @@ static const char *LAYERTYPENAMES[CD_NUMTYPES] = {
     "CDPropFloat3",
     "CDPropFloat2",
     "CDPropBoolean",
+    "CDHairLength",
 };
 
 const CustomData_MeshMasks CD_MASK_BAREMESH = {
diff --git a/source/blender/draw/engines/eevee/eevee_cryptomatte.c b/source/blender/draw/engines/eevee/eevee_cryptomatte.c
index 49780abc6f4..ea60dd0753e 100644
--- a/source/blender/draw/engines/eevee/eevee_cryptomatte.c
+++ b/source/blender/draw/engines/eevee/eevee_cryptomatte.c
@@ -255,7 +255,7 @@ static void eevee_cryptomatte_hair_cache_populate(EEVEE_Data *vedata,
 {
   DRWShadingGroup *grp = eevee_cryptomatte_shading_group_create(
       vedata, sldata, ob, material, true);
-  DRW_shgroup_hair_create_sub(ob, psys, md, grp);
+  DRW_shgroup_hair_create_sub(ob, psys, md, grp, NULL);
 }
 
 void EEVEE_cryptomatte_object_hair_cache_populate(EEVEE_Data *vedata,
diff --git a/source/blender/draw/engines/eevee/eevee_materials.c b/source/blender/draw/engines/eevee/eevee_materials.c
index 9ecb737192e..5f45e2184aa 100644
--- a/source/blender/draw/engines/eevee/eevee_materials.c
+++ b/source/blender/draw/engines/eevee/eevee_materials.c
@@ -769,15 +769,15 @@ static void eevee_hair_cache_populate(EEVEE_Data *vedata,
   EeveeMaterialCache matcache = eevee_material_cache_get(vedata, sldata, ob, matnr - 1, true);
 
   if (matcache.depth_grp) {
-    *matcache.depth_grp_p = DRW_shgroup_hair_create_sub(ob, psys, md, matcache.depth_grp);
+    *matcache.depth_grp_p = DRW_shgroup_hair_create_sub(ob, psys, md, matcache.depth_grp, NULL);
     DRW_shgroup_add_material_resources(*matcache.depth_grp_p, matcache.shading_gpumat);
   }
   if (matcache.shading_grp) {
-    *matcache.shading_grp_p = DRW_shgroup_hair_create_sub(ob, psys, md, matcache.shading_grp);
+    *matcache.shading_grp_p = DRW_shgroup_hair_create_sub(ob, psys, md, matcache.shading_grp, matcache.shading_gpumat);
     DRW_shgroup_add_material_resources(*matcache.shading_grp_p, matcache.shading_gpumat);
   }
   if (matcache.shadow_grp) {
-    *matcache.shadow_grp_p = DRW_shgroup_hair_create_sub(ob, psys, md, matcache.shadow_grp);
+    *matcache.shadow_grp_p = DRW_shgroup_hair_create_sub(ob, psys, md, matcache.shadow_grp, NULL);
     DRW_shgroup_add_material_resources(*matcache.shadow_grp_p, matcache.shading_gpumat);
     *cast_shadow = true;
   }
diff --git a/source/blender/draw/engines/eevee/eevee_motion_blur.c b/source/blender/draw/engines/eevee/eevee_motion_blur.c
index 2e200c8e053..e8c2514d908 100644
--- a/source/blender/draw/engines/eevee/eevee_motion_blur.c
+++ b/source/blender/draw/engines/eevee/eevee_motion_blur.c
@@ -269,7 +269,7 @@ void EEVEE_motion_blur_hair_cache_populate(EEVEE_ViewLayerData *UNUSED(sldata),
       GPUTexture *tex_prev = mb_hair->psys[psys_id].hair_pos_tx[MB_PREV];
       GPUTexture *tex_next = mb_hair->psys[psys_id].hair_pos_tx[MB_NEXT];
 
-      grp = DRW_shgroup_hair_create_sub(ob, psys, md, effects->motion_blur.hair_grp);
+      grp = DRW_shgroup_hair_create_sub(ob, psys, md, effects->motion_blur.hair_grp, NULL);
       DRW_shgroup_uniform_mat4(grp, "prevModelMatrix", mb_data->obmat[MB_PREV]);
       DRW_shgroup_uniform_mat4(grp, "currModelMatrix", mb_data->obmat[MB_CURR]);
       DRW_shgroup_uniform_mat4(grp, "nextModelMatrix", mb_data->obmat[MB_NEXT]);
diff --git a/source/blender/draw/engines/workbench/workbench_engine.c b/source/blender/draw/engines/workbench/workbench_engine.c
index 635aa7cef25..a5281427fa8 100644
--- a/source/blender/draw/engines/workbench/workbench_engine.c
+++ b/source/blender/draw/engines/workbench/workbench_engine.c
@@ -238,7 +238,7 @@ static void workbench_cache_hair_populate(WORKBENCH_PrivateData *wpd,
                              workbench_image_hair_setup(wpd, ob, matnr, ima, NULL, state) :
                              workbench_material_hair_setup(wpd, ob, matnr, color_type);
 
-  DRW_shgroup_hair_create_sub(ob, psys, md, grp);
+  DRW_shgroup_hair_create_sub(ob, psys, md, grp, NULL);
 }
 
 /**
diff --git a/source/blender/draw/intern/draw_cache_impl_curve.cc b/source/blender/draw/intern/draw_cache_impl_curve.cc
index 0804745fab5..dc8f382b7f8 100644
--- a/source/blender/draw/intern/draw_cache_impl_curve.cc
+++ b/source/blender/draw/intern/draw_cache_impl_curve.cc
@@ -342,6 +342,9 @@ static void curve_cd_calc_used_gpu_layers(CustomDataMask *cd_layers,
         case CD_ORCO:
           *cd_layers |= CD_MASK_ORCO;
           break;
+        case CD_HAIRLENGTH:
+          *cd_layers |= CD_MASK_HAIRLENGTH;
+          break;
       }
     }
   }
diff --git a/source/blender/draw/intern/draw_cache_impl_hair.c b/source/blender/draw/intern/draw_cache_impl_hair.c
index 6424b21666d..82af32c4c9f 100644
--- a/source/blender/draw/intern/draw_cache_impl_hair.c
+++ b/source/blender/draw/intern/draw_cache_impl_hair.c
@@ -30,6 +30,7 @@
 #include "BLI_math_base.h"
 #include "BLI_math_vector.h"
 #include "BLI_utildefines.h"
+#include "BLI_listbase.h"
 
 #include "DNA_hair_types.h"
 #include "DNA_object_types.h"
@@ -38,6 +39,7 @@
 
 #include "GPU_batch.h"
 #include "GPU_texture.h"
+#include "GPU_material.h"
 
 #include "draw_cache_impl.h"   /* own include */
 #include "draw_hair_private.h" /* own include */
@@ -141,7 +143,7 @@ static void ensure_seg_pt_count(Hair *hair, ParticleHairCache *hair_cache)
   }
 }
 
-static void hair_batch_cache_fill_segments_proc_pos(Hair *hair, GPUVertBufRaw *attr_step)
+static void hair_batch_cache_fill_segments_proc_pos(Hair *hair, GPUVertBufRaw *attr_step, GPUVertBufRaw *length_step)
 {
   /* TODO: use hair radius layer if available. */
   HairCurve *curve = hair->curves;
@@ -162,6 +164,8 @@ static void hair_batch_cache_fill_segments_proc_pos(Hair *hair, GPUVertBufRaw *a
       seg_data[3] = total_len;
       co_prev = curve_co[j];
     }
+    /* Assign length value*/
+    *(float *)GPU_vertbuf_raw_step(length_step) = total_len; 
     if (total_len > 0.0f) {
       /* Divide by total length to have a [0-1] number. */
       for (int j = 0; j < curve->numpoints; j++, seg_data_first += 4) {
@@ -171,28 +175,48 @@ static void hair_batch_cache_fill_segments_proc_pos(Hair *hair, GPUVertBufRaw *a
   }
 }
 
-static void hair_batch_cache_ensure_procedural_pos(Hair *hair, ParticleHairCache *cache)
+static void hair_batch_cache_ensure_procedural_pos(Hair *hair,
+                                                   ParticleHairCache *cache,
+                                                   GPUMaterial *gpu_material)
 {
-  if (cache->proc_point_buf != NULL) {
-    return;
-  }
+  if (cache->proc_point_buf == NULL) {
+    /* initialize vertex format */
+    GPUVertFormat format = {0};
+    uint pos_id = GPU_vertformat_attr_add(&format, "posTime", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);
 
-  /* initialize vertex format */
-  GPUVertFormat format = {0};
-  uint pos_id = GPU_vertformat_attr_add(&format, "posTime", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);
+    cache->proc_point_buf = GPU_vertbuf_create_with_format(&format);
+    GPU_vertbuf_data_alloc(cache->proc_point_buf, cache->point_len);
 
-  cache->proc_point_buf = GPU_vertbuf_create_with_format(&format);
-  GPU_vertbuf_data_alloc(cache->proc_point_buf, cache->point_len);
+    GPUVertBufRaw point_step;
+    GPU_vertbuf_attr_get_raw_data(cache->proc_point_buf, pos_id, &point_step);
 
-  GPUVertBufRaw pos_step;
-  GPU_vertbuf_attr_get_raw_data(cache->proc_point_buf, pos_id, &pos_step);
+    GPUVertFormat length_format = {0};
+    uint length_id = GPU_vertformat_attr_add(
+        &length_format, "hairLength", GPU_COMP_F32, 1, GPU_FETCH_FLOAT);
 
-  hair_batch_cache_fill_segments_proc_pos(hair, &pos_step);
+    cache->proc_length_buf = GPU_vertbuf_create_with_format(&length_format);
+    GPU_vertbuf_data_alloc(cache->proc_length_buf, cache->strands_len);
 
-  /* Create vbo immediately to bind to texture buffer. */
-  GPU_vertbuf_use(cache->proc_point_buf);
+    GPUVertBufRaw length_step;
+    GPU_vertbuf_attr_get_raw_data(cache->proc_length_buf, length_id, &length_step);
+
+    hair_batch_cache_fill_segments_proc_pos(hair, &point_step, &length_step);
 
-  cache->point_tex = GPU_texture_create_from_vertbuf("hair_point", cache->proc_point_buf);
+    /* Create vbo immediately to bind to texture buffer. */
+    GPU_vertbuf_use(cache->proc_point_buf);
+    cache->point_tex = GPU_texture_create_from_vertbuf("hair_point", cache->proc_point_buf);
+  }
+
+  if (gpu_material && cache->proc_length_buf != NULL && cache->length_tex) {
+    ListBase gpu_attrs = GPU_material_attributes(gpu_material);
+    LISTBASE_FOREACH (GPUMaterialAttribute *, attr, &gpu_attrs) {
+      if (attr->type == CD_HAIRLENGTH) {
+        GPU_vertbuf_use(cache->proc_length_buf);
+        cache->length_tex = GPU_texture_create_from_vertbuf("hair_length", cache->proc_length_buf);
+        break;
+      }
+    }
+  }
 }
 
 static void hair_batch_cache_fill_strands_data(Hair *hair,
@@ -310,6 +334,7 @@ static void hair_batch_cache_ensure_procedural_indices(Hair *hair,
 /* Ensure all textures and buffers needed for GPU accelerated drawing. */
 bool hair_ensure_procedural_data(Object *object,
                                  ParticleHairCache **r_hair_cache,
+                                 GPUMaterial *gpu_material,
                                  int subdiv,
                                  int thickness_res)
 {
@@ -325,7 +350,7 @@ bool hair_ensure_procedural_data(Object *object,
   /* Refreshed on combing and simulation. */
   if ((*r_hair_cache)->proc_point_buf == NULL) {
     ensure_seg_pt_count(hair, &cache->hair);
-    hair_batch_cache_ensure_procedural_pos(hair, &cache->hair);
+    hair_batch_cache_ensure_procedural_pos(hair, &cache->hair, gpu_material);
     need_ft_update = true;
   }
 
diff --git a/source/blender/draw/intern/draw_cache_impl_particles.c b/source/blender/draw/intern/draw_cache_impl_particles.c
index 5c51f24a435..387c43741f7 100644
--- a/source/blender/draw/intern/draw_cache_impl_particles.c
+++ b/source/blender/draw/intern/draw_cache_impl_particles.c
@@ -46,6 +46,7 @@
 #include "ED_particle.h"
 
 #include "GPU_batch.h"
+#include "GPU_material.h"
 
 #include "DEG_depsgraph_query.h"
 
@@ -183,7 +184,9 @@ void particle_batch_cache_clear_hair(ParticleHairCache *hair_cache)
 {
   /* TODO: more granular update tagging. */
   GPU_VERTBUF_DISCARD_SAFE(hair_cache->proc_point_buf);
+  GPU_VERTBUF_DISCARD_SAFE(hair_cache->proc_length_buf);
   DRW_TEXTURE_FREE_SAFE(hair_cache->point_tex);
+  DRW_TEXTURE_FREE_SAFE(hair_cache->length_tex);
 
   GPU_VERTBUF_DISCARD_SAFE(hair_cache->proc_strand_buf);
   GPU_VERTBUF_DISCARD_SAFE(hair_cache->proc_strand_seg_buf);
@@ -609,7 +612,8 @@ static int particle_batch_cache_fill_segments(ParticleSystem *psys,
 
 static void particle_batch_cache_fill_segments_proc_pos(ParticleCacheKey **path_cache,
                                                         const int num_path_keys,
-                                                        GPUVertBufRaw *attr_step)
+                                                        GPUVertBufRaw *attr_step,
+                                                        GPUVertBufRaw *length_step)
 {
   for (int i = 0; i < num_path_keys; i++) {
     ParticleCacheKey *path = path_cache[i];
@@ -630,6 +634,8 @@ static void particle_batch_cache_fill_segments_proc_pos(ParticleCacheKey **path_
       seg_data[3] = total_len;
       co_prev = path[j].co;
     }
+    /* Assign length value*/
+    *(float *)GPU_vertbuf_raw_step(length_step) = total_len;
     if (total_len > 0.0f) {
       /* Divide by total length to have a [0-1] number. */
       for (int j = 0; j <= path->segments; j++, seg_data_first += 4) {
@@ -1079,40 +1085,64 @@ static void particle_batch_cache_ensure_procedural_indices(PTCacheEdit *edit,
 
 static void particle_batch_cache_ensure_procedural_pos(PTCacheEdit *edit,
                                                        ParticleSystem *psys,
-                                                       ParticleHairCache *cache)
+                                                       ParticleHairCache *cache,
+                                                       GPUMaterial *gpu_material)
 {
-  if (cache->proc_point_buf != NULL) {
-    return;
-  }
+  if (cache->proc_point_buf == NULL) {
+    /* initialize vertex format */
+    GPUVertFormat pos_format = {0};
+    uint pos_id = GPU_vertformat_attr_add(
+        &pos_format, "posTime", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);
 
-  /* initialize vertex format */
-  GPUVertFormat format = {0};
-  uint pos_id = GPU_vertformat_attr_add(&format, "posTime", GPU_COMP_F32, 4, GPU_FETCH_FLOAT);
+    cache->proc_point_buf = GPU_vertbuf_create_with_format(&pos_format);
+    GPU_vertbuf_data_alloc(cache->proc_point_buf, cache->point_len);
 
-  cache->proc_point_buf = GPU_vertbuf_create_with_format(&format);
-  GPU_vertbuf_data_alloc(cache->proc_point_buf, cache->point_len);
+    GPUVertBufRaw pos_step;
+    GPU_vertbuf_attr_get_raw_data(cache->proc_point_buf, pos_id, &pos_step);
 
-  GPUVertBufRaw pos_step;
-  GPU_vertbuf_attr_get_raw_data(cache->proc_point_buf, pos_id, &pos_step);
+    GPUVertFormat length_format = {0};
+    uint length_id = GPU_vertformat_attr_add(
+        &length_format, "hairLength", GPU_COMP_F32, 1, GPU_FETCH_FLOAT);
 
-  if (edit != NULL && edit->pathcache != NULL) {
-    particle_batch_cache_fill_segments_proc_pos(edit->pathcache, edit->totcached, &pos_step);
-  }
-  else {
-    if ((psys->pathcache != NULL) &&
-        (!psys->childcache || (psys->part->draw & PART_DRAW_PARENT))) {
-      particle_batch_cache_fill_segments_proc_pos(psys->pathcache, psys->totpart, &pos_step);
+    cache->proc_length_buf = GPU_vertbuf_create_with_format(&length_format);
+    GPU_vertbuf_data_alloc(cache->proc_length_buf, cache->strands_len);
+
+    GPUVertBufRaw length_step;
+    GPU_vertbuf_attr_get_raw_data(cache->proc_length_buf, length_id, &length_step);
+
+    if (edit != NULL && edit->pathcache != NULL) {
+      particle_batch_cache_fill_segments_proc_pos(
+          edit->pathcache, edit->totcached, &pos_step, &length_step);
     }
-    if (psys->childcache) {
-      const int child_count = psys->totchild * psys->part->disp / 100;
-      particle_batch_cache_fill_segments_proc_pos(psys->childcache, child_count, &pos_step);
+    else {
+      if ((psys->pathcache != NULL) &&
+          (!psys->childcache || (psys->part->draw & PART_DRAW_PARENT))) {
+        particle_batch_cache_fill_segments_proc_pos(
+            psys->pathcache, psys->totpart, &pos_step, &length_step);
+      }
+      if (psys->childcache) {
+        const int child_count = psys->totchild * psys->part->disp / 100;
+        particle_batch_cache_fill_segments_proc_pos(
+            psys->childcache, child_count, &pos_step, &length_step);
+      }
     }
-  }
 
-  /* Create vbo immediately to bind to texture buffer. */
-  GPU_vertbuf_use(cache->proc_point_buf);
+    /* Create vbo immediately to bind to texture buffer. */
+    GPU_vertbuf_use(cache->proc_point_buf);
+    cache->point_tex = GPU_texture_create_from_vertbuf("part_point", cache->proc_point_buf);
+  }
 
-  cache->point_tex = GPU_texture_create_from_vertbuf("part_point", cache->proc_point_buf);
+  /* Checking hair length seperatly, only allocating gpu memory when needed */
+  if (gpu_material && cache->proc_length_buf != NULL && cache->length_tex == NULL) {
+    ListBase gpu_attrs = GPU_material_attributes(gpu_material);
+    LISTBASE_FOREACH (GPUMaterialAttribute *, attr, &gpu_attrs) {
+      if (attr->type == CD_HAIRLENGTH) {
+        GPU_vertbuf_use(cache->proc_length_buf);
+        cache->length_tex = GPU_texture_create_from_vertbuf("hair_length", cache->proc_length_buf);
+        break;
+      }
+    }
+  }
 }
 
 static void particle_batch_cache_ensure_pos_and_seg(PTCacheEdit *edit,
@@ -1649,6 +1679,7 @@ bool particles_ensure_procedural_data(Object *object,
                                       ParticleSystem *psys,
                                       ModifierData *md,
                                       ParticleHairCache **r_hair_cache,
+                                      GPUMaterial *gpu_material,
                                       int subdiv,
                                       int thickness_res)
 {
@@ -1666,9 +1697,9 @@ bool particles_ensure_procedural_data(Object *object,
   (*r_hair_cache)->final[subdiv].strands_res = 1 << (part->draw_step + subdiv);
 
   /* Refreshed on combing and simulation. */
-  if ((*r_hair_cache)->proc_point_buf == NULL) {
+  if ((*r_hair_cache)->proc_point_buf == NULL || (gpu_material && (*r_hair_cache)->length_tex == NULL)) {
     ensure_seg_pt_count(source.edit, source.psys, &cache->hair);
-    particle_batch_cache_ensure_procedural_pos(source.edit, source.psys, &cache->hair);
+    particle_batch_cache_ensure_procedural_pos(source.edit, source.psys, &cache->hair, gpu_material);
     need_ft_update = true;
   }
 
diff --git a/source/blender/draw/intern/draw_common.h b/source/blender/draw/intern/draw_common.h
index 1eaf2bee236..2913877c9c1 100644
--- a/source/blender/draw/intern/draw_common.h
+++ b/source/blender/draw/intern/draw_common.h
@@ -29,6 +29,7 @@ struct Object;
 struct ParticleSystem;
 struct RegionView3D;
 struct ViewLayer;
+struct GPUMaterial;
 
 #define UBO_FIRST_COLOR colorWire
 #define UBO_LAST_COLOR colorUVShadow
@@ -175,7 +176,8 @@ bool DRW_object_axis_orthogonal_to_view(struct Object *ob, int axis);
 struct DRWShadingGroup *DRW_shgroup_hair_create_sub(struct Object *object,
                                                     struct ParticleSystem *psys,
                                                     struct ModifierData *md,
-                                                    struct DRWShadingGroup *shgrp);
+                                                    struct DRWShadingGroup *shgrp,
+                                                    struct GPUMaterial *gpu_material);
 struct GPUVertBuf *DRW_hair_pos_buffer_get(struct Object *object,
                                            struct ParticleSystem *psys,
                                            struct ModifierData *md);
diff --git a/source/blender/draw/intern/draw_hair.c b/source/blender/draw/intern/draw_hair.c
index c2e25389091..75bef12285b 100644
--- a/source/blender/draw/intern/draw_hair.c
+++ b/source/blender/draw/intern/draw_hair.c
@@ -41,6 +41,7 @@
 #include "GPU_shader.h"
 #include "GPU_texture.h"
 #include "GPU_vertex_buffer.h"
+#include "GPU_material.h"
 
 #include "draw_hair_private.h"
 #include "draw_shader.h"
@@ -173,17 +174,17 @@ static void drw_hair_particle_cache_update_transform_feedback(ParticleHairCache
 }
 
 static ParticleHairCache *drw_hair_particle_cache_get(
-    Object *object, ParticleSystem *psys, ModifierData *md, int subdiv, int thickness_res)
+    Object *object, ParticleSystem *psys, ModifierData *md, GPUMaterial* gpu_material, int subdiv, int thickness_res)
 {
   bool update;
   ParticleHairCache *cache;
   if (psys) {
     /* Old particle hair. */
-    update = particles_ensure_procedural_data(object, psys, md, &cache, subdiv, thickness_res);
+    update = particles_ensure_procedural_data(object, psys, md, &cache, gpu_material, subdiv, thickness_res);
   }
   else {
     /* New hair object. */
-    update = hair_ensure_procedural_data(object, &cache, subdiv, thickness_res);
+    update = hair_ensure_procedural_data(object, &cache, gpu_material, subdiv, thickness_res);
   }
 
   if (update) {
@@ -206,7 +207,7 @@ GPUVertBuf *DRW_hair_pos_buffer_get(Object *object, ParticleSystem *psys, Modifi
   int subdiv = scene->r.hair_subdiv;
   int thickness_res = (scene->r.hair_type == SCE_HAIR_SHAPE_STRAND) ? 1 : 2;
 
-  ParticleHairCache *cache = drw_hair_particle_cache_get(object, psys, md, subdiv, thickness_res);
+  ParticleHairCache *cache = drw_hair_particle_cache_get(object, psys, md, NULL, subdiv, thickness_res);
 
   return cache->final[subdiv].proc_buf;
 }
@@ -248,7 +249,8 @@ void DRW_hair_duplimat_get(Object *object,
 DRWShadingGroup *DRW_shgroup_hair_create_sub(Object *object,
                                              ParticleSystem *psys,
                                              ModifierData *md,
-                                             DRWShadingGroup *shgrp_parent)
+                                             DRWShadingGroup *shgrp_parent,
+                                             GPUMaterial* gpu_material)
 {
   const DRWContextState *draw_ctx = DRW_context_state_get();
   Scene *scene = draw_ctx->scene;
@@ -258,7 +260,7 @@ DRWShadingGroup *DRW_shgroup_hair_create_sub(Object *object,
   int thickness_res = (scene->r.hair_type == SCE_HAIR_SHAPE_STRAND) ? 1 : 2;
 
   ParticleHairCache *hair_cache = drw_hair_particle_cache_get(
-      object, psys, md, subdiv, thickness_res);
+      object, psys, md, gpu_material, subdiv, thickness_res);
 
   DRWShadingGroup *shgrp = DRW_shgroup_create_sub(shgrp_parent);
 
@@ -308,6 +310,8 @@ DRWShadingGroup *DRW_shgroup_hair_create_sub(Object *object,
   }
 
   DRW_shgroup_uniform_texture(shgrp, "hairPointBuffer", hair_cache->final[subdiv].proc_tex);
+  if (hair_cache->length_tex)
+    DRW_shgroup_uniform_texture(shgrp, "hairLen", hair_cache->length_tex);
   DRW_shgroup_uniform_int(shgrp, "hairStrandsRes", &hair_cache->final[subdiv].strands_res, 1);
   DRW_shgroup_uniform_int_copy(shgrp, "hairThicknessRes", thickness_res);
   DRW_shgroup_uniform_float_copy(shgrp, "hairRadShape", hair_rad_shape);
diff --git a/source/blender/draw/intern/draw_hair_private.h b/source/blender/draw/intern/draw_hair_private.h
index 1f58d8d0ead..289a1690fc6 100644
--- a/source/blender/draw/intern/draw_hair_private.h
+++ b/source/blender/draw/intern/draw_hair_private.h
@@ -66,6 +66,10 @@ typedef struct ParticleHairCache {
   GPUVertBuf *proc_strand_buf;
   GPUTexture *strand_tex;
 
+  /* Hair Length */
+  GPUVertBuf *proc_length_buf;
+  GPUTexture *length_tex;
+
   GPUVertBuf *proc_strand_seg_buf;
   GPUTexture *strand_seg_tex;
 
@@ -93,11 +97,13 @@ bool particles_ensure_procedural_data(struct Object *object,
                                       struct ParticleSystem *psys,
                                       struct ModifierData *md,
                                       struct ParticleHairCache **r_hair_cache,
+                                      struct GPUMaterial *gpu_material,
                                       int subdiv,
                                       int thickness_res);
 
 bool hair_ensure_procedural_data(struct Object *object,
                                  struct ParticleHairCache **r_hair_cache,
+                                 struct GPUMaterial *gpu_material,
                                  int subdiv,
                                  int thickness_res);
 
diff --git a/source/blender/draw/intern/shaders/common_hair_lib.glsl b/source/blender/draw/intern/shaders/common_hair_lib.glsl
index 02c335ddae2..6cc7f09a852 100644
--- a/source/blender/draw/intern/shaders/common_hair_lib.glsl
+++ b/source/blender/draw/intern/shaders/common_hair_lib.glsl
@@ -210,6 +210,12 @@ void hair_get_pos_tan_binor_time(bool is_persp,
   }
 }
 
+float hair_get_customdata_float(const samplerBuffer cd_buf)
+{
+  int id = hair_get_strand_id();
+  return texelFetch(cd_buf, id).r;
+}
+
 vec2 hair_get_customdata_vec2(const samplerBuffer cd_buf)
 {
   int id = hair_get_strand_id();
diff --git a/source/blender/gpu/intern/gpu_codegen.c b/source/blender/gpu/intern/gpu_codegen.c
index bb1ebc0e85d..bbe939b546b 100644
--- a/source/blender/gpu/intern/gpu_codegen.c
+++ b/source/blender/gpu/intern/gpu_codegen.c
@@ -656,6 +656,8 @@ static const char *attr_prefix_get(CustomDataType type)
       return "c";
     case CD_AUTO_FROM_NAME:
       return "a";
+    case CD_HAIRLENGTH:
+      return "hl";
     default:
       BLI_assert_msg(0, "GPUVertAttr Prefix type not found : This should not happen!");
       return "";
@@ -675,7 +677,12 @@ static char *code_generate_interface(GPUNodeGraph *graph, int builtins)
   BLI_dynstr_append(ds, "\n");
 
   LISTBASE_FOREACH (GPUMaterialAttribute *, attr, &graph->attributes) {
-    BLI_dynstr_appendf(ds, "%s var%d;\n", gpu_data_type_to_string(attr->gputype), attr->id);
+    if (attr->type == CD_HAIRLENGTH) {
+      BLI_dynstr_appendf(ds, "float var%d;\n", attr->id);
+    }
+    else {
+      BLI_dynstr_appendf(ds, "%s var%d;\n", gpu_data_type_to_string(attr->gputype), attr->id);
+    }
   }
   if (builtins & GPU_BARYCENTRIC_TEXCO) {
     BLI_dynstr_append(ds, "vec2 barycentricTexCo;\n");
@@ -711,6 +718,11 @@ static char *code_generate_vertex(GPUNodeGraph *graph,
       BLI_dynstr_append(ds, datatoc_gpu_shader_common_obinfos_lib_glsl);
       BLI_dynstr_append(ds, "DEFINE_ATTR(vec4, orco);\n");
     }
+    if (attr->type == CD_HAIRLENGTH)
+    {
+      BLI_dynstr_append(ds, datatoc_gpu_shader_common_obinfos_lib_glsl);
+      BLI_dynstr_append(ds, "DEFINE_ATTR(float, hairLen);\n");
+    }
     else if (attr->name[0] == '\0') {
       BLI_dynstr_appendf(ds, "DEFINE_ATTR(%s, %s);\n", type_str, prefix);
       BLI_dynstr_appendf(ds, "#define att%d %s\n", attr->id, prefix);
@@ -755,6 +767,10 @@ static char *code_generate_vertex(GPUNodeGraph *graph,
       BLI_dynstr_appendf(
           ds, "  var%d = orco_get(position, modelmatinv, OrcoTexCoFactors, orco);\n", attr->id);
     }
+    else if (attr->type == CD_HAIRLENGTH) {
+      BLI_dynstr_appendf(
+          ds, "  var%d = hair_len_get(hair_get_strand_id(), hairLen);\n", attr->id);
+    }
     else {
       const char *type_str = gpu_data_type_to_string(attr->gputype);
       BLI_dynstr_appendf(ds, "  var%d = GET_ATTR(%s, att%d);\n", attr->id, type_str, attr->id);
diff --git a/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl b/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl
index f7bf3d33361..193a4190cbf 100644
--- a/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl
@@ -42,6 +42,11 @@ vec3 orco_get(vec3 local_pos, mat4 modelmatinv, vec4 orco_madd[2], const sampler
   return orco_madd[0].xyz + orco * orco_madd[1].xyz;
 }
 
+float hair_len_get(int id, const samplerBuffer len)
+{
+  return texelFetch(len, id).x;
+}
+
 vec4 tangent_get(const samplerBuffer attr, mat3 normalmat)
 {
   /* Unsupported */
@@ -71,6 +76,11 @@ vec3 orco_get(vec3 local_pos, mat4 modelmatinv, vec4 orco_madd[2], vec4 orco)
   }
 }
 
+float hair_len_get(int id, const float len)
+{
+  return len;
+}
+
 vec4 tangent_get(vec4 attr, mat3 normalmat)
 {
   vec4 tangent;
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_hair_info.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_hair_info.glsl
index 6330daa4391..6ffa6b59572 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_hair_info.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_hair_info.glsl
@@ -10,12 +10,15 @@ float wang_hash_noise(uint s)
   return fract(float(s) / 4294967296.0);
 }
 
-void node_hair_info(out float is_strand,
+void node_hair_info(float hair_length,
+                    out float is_strand,
                     out float intercept,
+                    out float length,
                     out float thickness,
                     out vec3 tangent,
                     out float random)
 {
+  length = hair_length;
 #ifdef HAIR_SHADER
   is_strand = 1.0;
   intercept = hairTime;
diff --git a/source/blender/makesdna/DNA_customdata_types.h b/source/blender/makesdna/DNA_customdata_types.h
index 6acea8da15f..36bdd4915ff 100644
--- a/source/blender/makesdna/DNA_customdata_types.h
+++ b/source/blender/makesdna/DNA_customdata_types.h
@@ -84,7 +84,8 @@ typedef struct CustomData {
    * MUST be >= CD_NUMTYPES, but we can't use a define here.
    * Correct size is ensured in CustomData_update_typemap assert().
    */
-  int typemap[51];
+  int typemap[52];
+  char _pad[4];
   /** Number of layers, size of layers array. */
   int totlayer, maxlayer;
   /** In editmode, total size of all data layers. */
@@ -166,7 +167,9 @@ typedef enum CustomDataType {
 
   CD_PROP_BOOL = 50,
 
-  CD_NUMTYPES = 51,
+  CD_HAIRLENGTH = 51,
+
+  CD_NUMTYPES = 52,
 } CustomDataType;
 
 /* Bits for CustomDataMask */
@@ -220,6 +223,8 @@ typedef enum CustomDataType {
 #define CD_MASK_PROP_FLOAT2 (1ULL << CD_PROP_FLOAT2)
 #define CD_MASK_PROP_BOOL (1ULL << CD_PROP_BOOL)
 
+#define CD_MASK_HAIRLENGTH (1ULL << CD_HAIRLENGTH)
+
 /** Multires loop data. */
 #define CD_MASK_MULTIRES_GRIDS (CD_MASK_MDISPS | CD_GRID_PAINT_MASK)
 
diff --git a/source/blender/nodes/shader/nodes/node_shader_hair_info.c b/source/blender/nodes/shader/nodes/node_shader_hair_info.c
index 843185befb6..559c5cf7ae8 100644
--- a/source/blender/nodes/shader/nodes/node_shader_hair_info.c
+++ b/source/blender/nodes/shader/nodes/node_shader_hair_info.c
@@ -22,6 +22,7 @@
 static bNodeSocketTemplate outputs[] = {
     {SOCK_FLOAT, N_("Is Strand"), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
     {SOCK_FLOAT, N_("Intercept"), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
+    {SOCK_FLOAT, N_("Length"), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
     {SOCK_FLOAT, N_("Thickness"), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
     {SOCK_VECTOR, N_("Tangent Normal"), 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
     // { SOCK_FLOAT,  0, N_("Fade"),             0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f},
@@ -35,7 +36,11 @@ static int node_shader_gpu_hair_info(GPUMaterial *mat,
                                      GPUNodeStack *in,
                                      GPUNodeStack *out)
 {
-  return GPU_stack_link(mat, node, "node_hair_info", in, out);
+  /* Length: don't request length if not needed. */
+  const static float zero = 0;
+  GPUNodeLink *length_link = (!out[2].hasoutput) ? GPU_constant(&zero) :
+                                                   GPU_attribute(mat, CD_HAIRLENGTH, "");
+  return GPU_stack_link(mat, node, "node_hair_info", in, out, length_link);
 }
 
 /* node type definition */