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

3 files changed, 31 insertions, 2 deletions

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;