message: use baseColorfactor alpha for opacity
diff: @@ -1121,6 +1121,7 @@ NodePtr GLTFData::createOSPMaterial(const tinygltf::Material &mat)
  auto ospMat = createNode(matName, "principled");
  ospMat->createChild("baseColor", "rgb") = rgb(
  pbr.baseColorFactor[0], pbr.baseColorFactor[1], pbr.baseColorFactor[2]);
  + auto alpha = (float)pbr.baseColorFactor[3];
  ospMat->createChild("metallic", "float") = (float)pbr.metallicFactor;
  ospMat->createChild("roughness", "float") = (float)pbr.roughnessFactor;
  @@ -1134,7 +1135,7 @@ NodePtr GLTFData::createOSPMaterial(const tinygltf::Material &mat)
  if (mat.alphaMode == "OPAQUE")
  ospMat->createChild("opacity", "float") = 1.f;
  else if (mat.alphaMode == "BLEND")
  - ospMat->createChild("opacity", "float") = 1.f;
  + ospMat->createChild("opacity", "float") = alpha;
  else if (mat.alphaMode == "MASK")
  ospMat->createChild("opacity", "float") = 1.f - (float)mat.alphaCutoff;
  