Fix T73938: Cycles Vertex Color wrong if no layer is specified

The node would render black in this case (but should use the
'active_render' layer choosen in the object data properties -- this is
now in line to how this is handled for e.g. UVs)

This introduces ATTR_STD_VERTEX_COLOR and uses this thoughout, if no
particular layer is specified in the node.

Maniphest Tasks: T73938

Differential Revision: https://developer.blender.org/D6887

2 files changed, 30 insertions, 3 deletions

diff --git a/intern/cycles/render/attribute.cpp b/intern/cycles/render/attribute.cpp
index 05c0b5693bc..4fbf831087f 100644
--- a/intern/cycles/render/attribute.cpp
+++ b/intern/cycles/render/attribute.cpp
@@ -301,6 +301,8 @@ const char *Attribute::standard_name(AttributeStandard std)
       return "tangent";
     case ATTR_STD_UV_TANGENT_SIGN:
       return "tangent_sign";
+    case ATTR_STD_VERTEX_COLOR:
+      return "vertex_color";
     case ATTR_STD_POSITION_UNDEFORMED:
       return "undeformed";
     case ATTR_STD_POSITION_UNDISPLACED:
@@ -480,6 +482,9 @@ Attribute *AttributeSet::add(AttributeStandard std, ustring name)
       case ATTR_STD_UV_TANGENT_SIGN:
         attr = add(name, TypeDesc::TypeFloat, ATTR_ELEMENT_CORNER);
         break;
+      case ATTR_STD_VERTEX_COLOR:
+        attr = add(name,TypeRGBA, ATTR_ELEMENT_CORNER_BYTE);
+        break;
       case ATTR_STD_GENERATED:
       case ATTR_STD_POSITION_UNDEFORMED:
       case ATTR_STD_POSITION_UNDISPLACED:
diff --git a/intern/cycles/render/nodes.cpp b/intern/cycles/render/nodes.cpp
index 41b4b05ba19..9c909c2131f 100644
--- a/intern/cycles/render/nodes.cpp
+++ b/intern/cycles/render/nodes.cpp
@@ -4519,7 +4519,10 @@ VertexColorNode::VertexColorNode() : ShaderNode(node_type)
 void VertexColorNode::attributes(Shader *shader, AttributeRequestSet *attributes)
 {
   if (!(output("Color")->links.empty() && output("Alpha")->links.empty())) {
-    attributes->add_standard(layer_name);
+    if (layer_name != "")
+      attributes->add_standard(layer_name);
+    else
+      attributes->add(ATTR_STD_VERTEX_COLOR);
   }
   ShaderNode::attributes(shader, attributes);
 }
@@ -4528,7 +4531,14 @@ void VertexColorNode::compile(SVMCompiler &compiler)
 {
   ShaderOutput *color_out = output("Color");
   ShaderOutput *alpha_out = output("Alpha");
-  int layer_id = compiler.attribute(layer_name);
+  int layer_id = 0;
+
+  if (layer_name != "") {
+    layer_id = compiler.attribute(layer_name);
+  }
+  else {
+    layer_id = compiler.attribute(ATTR_STD_VERTEX_COLOR);
+  }
 
   ShaderNodeType node;
 
@@ -4555,7 +4565,19 @@ void VertexColorNode::compile(OSLCompiler &compiler)
   else {
     compiler.parameter("bump_offset", "center");
   }
-  compiler.parameter("layer_name", layer_name.c_str());
+
+  if (layer_name.empty()) {
+    compiler.parameter("layer_name", ustring("geom:vertex_color"));
+  }
+  else {
+    if (Attribute::name_standard(layer_name.c_str()) != ATTR_STD_NONE) {
+      compiler.parameter("name", (string("geom:") + layer_name.c_str()).c_str());
+    }
+    else {
+      compiler.parameter("layer_name", layer_name.c_str());
+    }
+  }
+
   compiler.add(this, "node_vertex_color");
 }