Fix T78447: Cycles vertex color node not working with hair

Referenced by issue #78447, Vertex Paint not showing on hair in Cycles and Viewport Vertex Color missing

intern/cycles/blender/blender_curves.cpp

@@ -262,7 +262,7 @@ static bool ObtainCacheParticleVcol(Hair *hair,
           BL::Mesh::vertex_colors_iterator l;
           b_mesh->vertex_colors.begin(l);
 
-          float3 vcol = make_float3(0.0f, 0.0f, 0.0f);
+          float4 vcol = make_float4(0.0f, 0.0f, 0.0f, 1.0f);
           if (b_mesh->vertex_colors.length())
             b_psys.mcol_on_emitter(psmd, *b_pa, pa_no, vcol_num, &vcol.x);
           CData->curve_vcol.push_back_slow(vcol);
@@ -578,16 +578,16 @@ void BlenderSync::sync_particle_hair(
       ObtainCacheParticleVcol(hair, &b_mesh, &b_ob, &CData, !preview, vcol_num);
 
       Attribute *attr_vcol = hair->attributes.add(
-          ustring(l->name().c_str()), TypeDesc::TypeColor, ATTR_ELEMENT_CURVE);
+          ustring(l->name().c_str()), TypeRGBA, ATTR_ELEMENT_CURVE);
 
-      float3 *fdata = attr_vcol->data_float3();
+      float4 *fdata = attr_vcol->data_float4();
 
       if (fdata) {
         size_t i = 0;
 
         /* Encode vertex color using the sRGB curve. */
         for (size_t curve = 0; curve < CData.curve_vcol.size(); curve++) {
-          fdata[i++] = color_srgb_to_linear_v3(CData.curve_vcol[curve]);
+          fdata[i++] = color_srgb_to_linear_v4(CData.curve_vcol[curve]);
         }
       }
     }

intern/cycles/kernel/geom/geom_curve.h

@@ -198,6 +198,66 @@ ccl_device float3 curve_attribute_float3(KernelGlobals *kg,
   }
 }
 
+ccl_device float4 curve_attribute_float4(KernelGlobals *kg,
+                                         const ShaderData *sd,
+                                         const AttributeDescriptor desc,
+                                         float4 *dx,
+                                         float4 *dy)
+{
+  if (desc.element == ATTR_ELEMENT_CURVE) {
+    /* idea: we can't derive any useful differentials here, but for tiled
+     * mipmap image caching it would be useful to avoid reading the highest
+     * detail level always. maybe a derivative based on the hair density
+     * could be computed somehow? */
+#  ifdef __RAY_DIFFERENTIALS__
+    if (dx)
+      *dx = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+    if (dy)
+      *dy = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+#  endif
+
+    return kernel_tex_fetch(__attributes_float3, desc.offset + sd->prim);
+  }
+  else if (desc.element == ATTR_ELEMENT_CURVE_KEY ||
+           desc.element == ATTR_ELEMENT_CURVE_KEY_MOTION) {
+    float4 curvedata = kernel_tex_fetch(__curves, sd->prim);
+    int k0 = __float_as_int(curvedata.x) + PRIMITIVE_UNPACK_SEGMENT(sd->type);
+    int k1 = k0 + 1;
+
+    float4 f0 = kernel_tex_fetch(__attributes_float3, desc.offset + k0);
+    float4 f1 = kernel_tex_fetch(__attributes_float3, desc.offset + k1);
+
+#  ifdef __RAY_DIFFERENTIALS__
+    if (dx)
+      *dx = sd->du.dx * (f1 - f0);
+    if (dy)
+      *dy = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+#  endif
+
+    return (1.0f - sd->u) * f0 + sd->u * f1;
+  }
+  else if (desc.element == ATTR_ELEMENT_OBJECT || desc.element == ATTR_ELEMENT_MESH) {
+#  ifdef __RAY_DIFFERENTIALS__
+    if (dx)
+      *dx = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+    if (dy)
+      *dy = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+#  endif
+
+    return kernel_tex_fetch(__attributes_float3, desc.offset);
+  }
+  else {
+#  ifdef __RAY_DIFFERENTIALS__
+    if (dx)
+      *dx = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+    if (dy)
+      *dy = make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+#  endif
+
+    return make_float4(0.0f, 0.0f, 0.0f, 0.0f);
+  }
+}
+
 /* Curve thickness */
 
 ccl_device float curve_thickness(KernelGlobals *kg, ShaderData *sd)

intern/cycles/kernel/geom/geom_primitive.h

@@ -174,6 +174,11 @@ ccl_device_inline float4 primitive_attribute_float4(KernelGlobals *kg,
     else
       return subd_triangle_attribute_float4(kg, sd, desc, dx, dy);
   }
+#ifdef __HAIR__
+  else if (sd->type & PRIMITIVE_ALL_CURVE) {
+    return curve_attribute_float4(kg, sd, desc, dx, dy);
+  }
+#endif
   else {
     if (dx)
       *dx = make_float4(0.0f, 0.0f, 0.0f, 0.0f);

intern/cycles/render/curves.h

@@ -50,7 +50,7 @@ class ParticleCurveData {
   array<int> curve_keynum;
   array<float> curve_length;
   array<float2> curve_uv;
-  array<float3> curve_vcol;
+  array<float4> curve_vcol;
 
   array<float3> curvekey_co;
   array<float> curvekey_time;