source/blender/nodes/shader/materialx/node_item.h

@@ -44,6 +44,9 @@ class NodeItem {
     Displacementshader,
     SurfaceShader,
     Material,
+
+    /* Special type to retrieve opacity for <surface> */
+    SurfaceOpacity,
   };
   enum class CompareOp { Less = 0, LessEq, Eq, GreaterEq, Greater, NotEq };
 

source/blender/nodes/shader/nodes/node_shader_add_shader.cc

@@ -25,7 +25,7 @@ static int node_shader_gpu_add_shader(GPUMaterial *mat,
 NODE_SHADER_MATERIALX_BEGIN
 #ifdef WITH_MATERIALX
 {
-  if (!ELEM(to_type_, NodeItem::Type::BSDF, NodeItem::Type::EDF)) {
+  if (!ELEM(to_type_, NodeItem::Type::BSDF, NodeItem::Type::EDF, NodeItem::Type::SurfaceOpacity)) {
     return empty();
   }
 
@@ -41,6 +41,9 @@ NODE_SHADER_MATERIALX_BEGIN
   if (!shader1 && shader2) {
     return shader2;
   }
+  if (to_type_ == NodeItem::Type::SurfaceOpacity) {
+    return (shader1 + shader2) * val(0.5f);
+  }
   return shader1 + shader2;
 }
 #endif

source/blender/nodes/shader/nodes/node_shader_bsdf_principled.cc

@@ -350,7 +350,7 @@ NODE_SHADER_MATERIALX_BEGIN
         {"coat_tint", get_input_value("Coat Tint", NodeItem::Type::Color3)},
         {"ior", get_input_value("IOR", NodeItem::Type::Float)},
         {"transmission", get_input_value("Transmission Weight", NodeItem::Type::Float)},
-        //{"alpha", get_input_value("Alpha", NodeItem::Type::Float)},
+        {"alpha", get_input_value("Alpha", NodeItem::Type::Float)},
         {"normal", get_input_link("Normal", NodeItem::Type::Vector3)},
         {"coat_normal", get_input_link("Coat Normal", NodeItem::Type::Vector3)},
         {"tangent", get_input_link("Tangent", NodeItem::Type::Vector3)},
@@ -572,9 +572,16 @@ NODE_SHADER_MATERIALX_BEGIN
            {"emission", in["emission"]},
            {"emission_color", in["emission_color"]},
            {"normal", in["normal"]},
-           {"tangent", in["tangent"]}});
+           {"tangent", in["tangent"]},
+           {"opacity", in["alpha"].convert(NodeItem::Type::Color3)}});
       break;
     }
+
+    case NodeItem::Type::SurfaceOpacity: {
+      res = get_input_value("Alpha", NodeItem::Type::Float);
+      break;
+    }
+
     default:
       BLI_assert_unreachable();
   }

source/blender/nodes/shader/nodes/node_shader_bsdf_transparent.cc

@@ -27,6 +27,26 @@ static int node_shader_gpu_bsdf_transparent(GPUMaterial *mat,
   return GPU_stack_link(mat, node, "node_bsdf_transparent", in, out);
 }
 
+NODE_SHADER_MATERIALX_BEGIN
+#ifdef WITH_MATERIALX
+{
+  switch (to_type_) {
+    case NodeItem::Type::BSDF: {
+      NodeItem color = get_input_value("Color", NodeItem::Type::Color3);
+      return create_node("oren_nayar_diffuse_bsdf", NodeItem::Type::BSDF, {{"color", color}});
+    }
+    case NodeItem::Type::SurfaceOpacity: {
+      NodeItem color = get_input_value("Color", NodeItem::Type::Color3);
+      return val(1.0f) - color.dotproduct(val(1.0f / 3.0f));
+    }
+    default:
+      break;
+  }
+  return empty();
+}
+#endif
+NODE_SHADER_MATERIALX_END
+
 }  // namespace blender::nodes::node_shader_bsdf_transparent_cc
 
 /* node type definition */
@@ -40,6 +60,7 @@ void register_node_type_sh_bsdf_transparent()
   ntype.add_ui_poll = object_shader_nodes_poll;
   ntype.declare = file_ns::node_declare;
   ntype.gpu_fn = file_ns::node_shader_gpu_bsdf_transparent;
+  ntype.materialx_fn = file_ns::node_shader_materialx;
 
   nodeRegisterType(&ntype);
 }

source/blender/nodes/shader/nodes/node_shader_light_falloff.cc

@@ -32,7 +32,7 @@ NODE_SHADER_MATERIALX_BEGIN
 
   /* This node isn't supported by MaterialX. This formula was given from OSL shader code in Cycles
    * node_light_falloff.osl. Considered ray_length=1.0f. */
-  return strength * val(1.0f) / (smooth + val(1.0f));
+  return strength / (smooth + val(1.0f));
 }
 #endif
 NODE_SHADER_MATERIALX_END

source/blender/nodes/shader/nodes/node_shader_mix_shader.cc

@@ -26,7 +26,7 @@ static int node_shader_gpu_mix_shader(GPUMaterial *mat,
 NODE_SHADER_MATERIALX_BEGIN
 #ifdef WITH_MATERIALX
 {
-  if (!ELEM(to_type_, NodeItem::Type::BSDF, NodeItem::Type::EDF)) {
+  if (!ELEM(to_type_, NodeItem::Type::BSDF, NodeItem::Type::EDF, NodeItem::Type::SurfaceOpacity)) {
     return empty();
   }
 

source/blender/nodes/shader/nodes/node_shader_output_material.cc

@@ -51,13 +51,10 @@ NODE_SHADER_MATERIALX_BEGIN
     NodeItem bsdf = get_input_link("Surface", NodeItem::Type::BSDF);
     NodeItem edf = get_input_link("Surface", NodeItem::Type::EDF);
     if (bsdf || edf) {
-      surface = create_node("surface", NodeItem::Type::SurfaceShader);
+      NodeItem opacity = get_input_link("Surface", NodeItem::Type::SurfaceOpacity);
-      if (bsdf) {
+      surface = create_node("surface",
-        surface.set_input("bsdf", bsdf);
+                            NodeItem::Type::SurfaceShader,
-      }
+                            {{"bsdf", bsdf}, {"edf", edf}, {"opacity", opacity}});
-      if (edf) {
-        surface.set_input("edf", edf);
-      }
     }
   }
   return create_node("surfacematerial", NodeItem::Type::Material, {{"surfaceshader", surface}});