message: Fix alphaMode by setting the correct opacity value
  Requires a change to OSPRay Principled Material
  (!487 or something similar)
diff: @@ -537,14 +537,13 @@ namespace ospray {
  ospMat->createChild("metallic", "float") = (float)pbr.metallicFactor;
  ospMat->createChild("roughness", "float") = (float)pbr.roughnessFactor;
  - if (mat.alphaMode == "MASK")
  + if (mat.alphaMode == "OPAQUE")
  + ospMat->createChild("opacity", "float") = 1.f;
  + else if (mat.alphaMode == "BLEND")
  + ospMat->createChild("opacity", "float") = 0.f;
  + else if (mat.alphaMode == "MASK")
  ospMat->createChild("opacity", "float") = (float) mat.alphaCutoff;
  - // XXX If alphaMode is BLEND, then alpha is taken from the baseColor
  - // Need to create an opacityMap from the baseColor[4] texture!!!
  - if (mat.alphaMode == "BLEND")
  - ospMat->createChild("opacity", "float") = (float)0.2;
  -
  // All textures *can* specify a texcoord other than 0. OSPRay only
  // supports one set of texcoords (TEXCOORD_0).
  @@ -552,10 +551,6 @@ namespace ospray {
  pbr.baseColorTexture.texCoord == 0) {
  // Used as a color texture, must be sRGB space, not linear
  setOSPTexture(ospMat, "baseColor", pbr.baseColorTexture.index, false);
  -
  - // Create a single channel textures from the baseColorTexture[4]
  - if (mat.alphaMode == "BLEND") {
  - }
  }
  // XXX Not sure exactly how to map these yet. Are they single component?
  