Alpha hash support for hair in EEvee

This patch adds support for alpha hash for hair rendering in EEvee.  Here's a comparison of with alpha hashing:

{F7588610}

And no alpha hashing:

{F7588615}

Note that this needs "soft shadows" enabled, otherwise shadows will be noisy; here's a render with soft shadows disabled:

{F7588621}

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D5221

1 files changed, 29 insertions, 0 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/shadow_vert.glsl b/source/blender/draw/engines/eevee/shaders/shadow_vert.glsl
index 6b06aab34d2..c42f905cf7e 100644
--- a/source/blender/draw/engines/eevee/shaders/shadow_vert.glsl
+++ b/source/blender/draw/engines/eevee/shaders/shadow_vert.glsl
@@ -9,6 +9,14 @@ out vec3 worldNormal;
 out vec3 viewNormal;
 #endif
 
+#ifdef HAIR_SHADER
+out vec3 hairTangent;
+out float hairThickTime;
+out float hairThickness;
+out float hairTime;
+flat out int hairStrandID;
+#endif
+
 void main()
 {
 #ifdef GPU_INTEL
@@ -18,13 +26,34 @@ void main()
   gl_Position.x = float(gl_VertexID);
 #endif
 
+#ifdef HAIR_SHADER
+  hairStrandID = hair_get_strand_id();
+  vec3 world_pos, binor;
+  hair_get_pos_tan_binor_time((ProjectionMatrix[3][3] == 0.0),
+                              ModelMatrixInverse,
+                              ViewMatrixInverse[3].xyz,
+                              ViewMatrixInverse[2].xyz,
+                              world_pos,
+                              hairTangent,
+                              binor,
+                              hairTime,
+                              hairThickness,
+                              hairThickTime);
+
+  worldNormal = cross(hairTangent, binor);
+#else
   vec3 world_pos = point_object_to_world(pos);
+#endif
+
   gl_Position = point_world_to_ndc(world_pos);
 #ifdef MESH_SHADER
   worldPosition = world_pos;
   viewPosition = point_world_to_view(worldPosition);
 
+#  ifndef HAIR_SHADER
   worldNormal = normalize(normal_object_to_world(nor));
+#  endif
+
   /* No need to normalize since this is just a rotation. */
   viewNormal = normal_world_to_view(worldNormal);
 #  ifdef USE_ATTR