Fix T97983 EEVEE: Tangent Normal of Curves info behaves differently in Eevee

Curve tangent was correctly mistaken with curve normal.

This patch fixes the name of the output in the glsl function and make curve
attributes more explicit (with `curve_` prefix).

This also improve the normal computation by making it per pixel to match
cycles.

Also ports the changes to eevee-next.

8 files changed, 21 insertions, 9 deletions

diff --git a/source/blender/draw/engines/eevee/shaders/surface_lib.glsl b/source/blender/draw/engines/eevee/shaders/surface_lib.glsl
index 1f2f7cb65cc..696e5d4c97b 100644
--- a/source/blender/draw/engines/eevee/shaders/surface_lib.glsl
+++ b/source/blender/draw/engines/eevee/shaders/surface_lib.glsl
@@ -112,6 +112,7 @@ GlobalData init_globals(void)
     surf.N = -surf.N;
   }
 #  ifdef HAIR_SHADER
+  vec3 V = cameraVec(surf.P);
   /* Shade as a cylinder. */
   vec3 B = normalize(cross(worldNormal, hairTangent));
   float cos_theta;
@@ -125,7 +126,10 @@ GlobalData init_globals(void)
   }
   float sin_theta = sqrt(max(0.0, 1.0 - cos_theta * cos_theta));
   surf.N = safe_normalize(worldNormal * sin_theta + B * cos_theta);
-  surf.T = hairTangent;
+  surf.curve_T = -hairTangent;
+  /* Costly, but follows cycles per pixel tangent space (not following curve shape). */
+  surf.curve_B = cross(V, surf.curve_T);
+  surf.curve_N = safe_normalize(cross(surf.curve_T, surf.curve_B));
   surf.is_strand = true;
   surf.hair_time = hairTime;
   surf.hair_thickness = hairThickness;
@@ -134,7 +138,7 @@ GlobalData init_globals(void)
   surf.barycentric_coords = hair_resolve_barycentric(hairBary);
 #    endif
 #  else
-  surf.T = vec3(0.0);
+  surf.curve_T = surf.curve_B = surf.curve_N = vec3(0.0);
   surf.is_strand = false;
   surf.hair_time = 0.0;
   surf.hair_thickness = 0.0;
diff --git a/source/blender/draw/engines/eevee_next/shaders/eevee_geom_curves_vert.glsl b/source/blender/draw/engines/eevee_next/shaders/eevee_geom_curves_vert.glsl
index 11f93ad0d14..708bd153e84 100644
--- a/source/blender/draw/engines/eevee_next/shaders/eevee_geom_curves_vert.glsl
+++ b/source/blender/draw/engines/eevee_next/shaders/eevee_geom_curves_vert.glsl
@@ -18,7 +18,7 @@ void main()
                               ViewMatrixInverse[3].xyz,
                               ViewMatrixInverse[2].xyz,
                               interp.P,
-                              T,
+                              interp.curves_tangent,
                               interp.curves_binormal,
                               interp.curves_time,
                               interp.curves_thickness,
diff --git a/source/blender/draw/engines/eevee_next/shaders/eevee_surf_lib.glsl b/source/blender/draw/engines/eevee_next/shaders/eevee_surf_lib.glsl
index 0d8644c9901..30b48edaa78 100644
--- a/source/blender/draw/engines/eevee_next/shaders/eevee_surf_lib.glsl
+++ b/source/blender/draw/engines/eevee_next/shaders/eevee_surf_lib.glsl
@@ -42,6 +42,12 @@ void init_globals_curves()
   float sin_theta = sqrt(max(0.0, 1.0 - cos_theta * cos_theta));
   g_data.N = normalize(interp.N * sin_theta + interp.curves_binormal * cos_theta);
 
+  /* Costly, but follows cycles per pixel tangent space (not following curve shape). */
+  vec3 V = cameraVec(g_data.P);
+  g_data.curve_T = -interp.curves_tangent;
+  g_data.curve_B = cross(V, g_data.curve_T);
+  g_data.curve_N = safe_normalize(cross(g_data.curve_T, g_data.curve_B));
+
   g_data.is_strand = true;
   g_data.hair_time = interp.curves_time;
   g_data.hair_thickness = interp.curves_thickness;
@@ -94,6 +100,7 @@ void init_interface()
   interp.P = vec3(0.0);
   interp.N = vec3(0.0);
   interp.barycentric_coords = vec2(0.0);
+  interp.curves_tangent = vec3(0.0);
   interp.curves_binormal = vec3(0.0);
   interp.curves_time = 0.0;
   interp.curves_time_width = 0.0;
diff --git a/source/blender/draw/engines/eevee_next/shaders/infos/eevee_material_info.hh b/source/blender/draw/engines/eevee_next/shaders/infos/eevee_material_info.hh
index e829a41d682..4d6895bcde0 100644
--- a/source/blender/draw/engines/eevee_next/shaders/infos/eevee_material_info.hh
+++ b/source/blender/draw/engines/eevee_next/shaders/infos/eevee_material_info.hh
@@ -54,6 +54,7 @@ GPU_SHADER_INTERFACE_INFO(eevee_surf_iface, "interp")
     .smooth(Type::VEC3, "P")
     .smooth(Type::VEC3, "N")
     .smooth(Type::VEC2, "barycentric_coords")
+    .smooth(Type::VEC3, "curves_tangent")
     .smooth(Type::VEC3, "curves_binormal")
     .smooth(Type::FLOAT, "curves_time")
     .smooth(Type::FLOAT, "curves_time_width")
diff --git a/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl b/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl
index 5c97eada77d..6091a5c834a 100644
--- a/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl
+++ b/source/blender/gpu/shaders/gpu_shader_codegen_lib.glsl
@@ -191,8 +191,8 @@ struct GlobalData {
   vec3 N;
   /** Geometric Normal. */
   vec3 Ng;
-  /** Surface default Tangent. */
-  vec3 T;
+  /** Curve Tangent Space. */
+  vec3 curve_T, curve_B, curve_N;
   /** Barycentric coordinates. */
   vec2 barycentric_coords;
   vec3 barycentric_dists;
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_geometry.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_geometry.glsl
index 5e86a4577ee..4c9ff31622f 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_geometry.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_geometry.glsl
@@ -18,7 +18,7 @@ void node_geometry(vec3 orco,
   true_normal = g_data.Ng;
 
   if (g_data.is_strand) {
-    tangent = g_data.T;
+    tangent = g_data.curve_T;
   }
   else {
     tangent_orco_z(orco, orco);
diff --git a/source/blender/gpu/shaders/material/gpu_shader_material_hair.glsl b/source/blender/gpu/shaders/material/gpu_shader_material_hair.glsl
index 7bf8795495a..b24f9ab65f0 100644
--- a/source/blender/gpu/shaders/material/gpu_shader_material_hair.glsl
+++ b/source/blender/gpu/shaders/material/gpu_shader_material_hair.glsl
@@ -40,7 +40,7 @@ void node_bsdf_hair_principled(vec4 color,
   hair_data.color = color.rgb;
   hair_data.offset = offset;
   hair_data.roughness = vec2(0.0);
-  hair_data.T = g_data.T;
+  hair_data.T = g_data.curve_B;
 
   result = closure_eval(hair_data);
 }
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 a8b4b039370..2d5114c3bad 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
@@ -5,14 +5,14 @@ void node_hair_info(float hair_length,
                     out float intercept,
                     out float out_length,
                     out float thickness,
-                    out vec3 tangent,
+                    out vec3 normal,
                     out float random)
 {
   is_strand = float(g_data.is_strand);
   intercept = g_data.hair_time;
   thickness = g_data.hair_thickness;
   out_length = hair_length;
-  tangent = g_data.T;
+  normal = g_data.curve_N;
   /* TODO: could be precomputed per strand instead. */
   random = wang_hash_noise(uint(g_data.hair_strand_id));
 }