message: Change the material if the type has changed in sg
diff: @@ -57,7 +57,13 @@ namespace ospray {
  void Material::preCommit(RenderContext &ctx)
  {
  assert(ctx.ospRenderer);
  - if (ospMaterial != nullptr && ospRenderer == ctx.ospRenderer) return;
  + const bool typeChanged =
  + child("type").lastModified() > child("type").lastCommitted();
  + if (!typeChanged && ospMaterial != nullptr
  + && ospRenderer == ctx.ospRenderer)
  + {
  + return;
  + }
  auto mat = ospNewMaterial(ctx.ospRenderer,
  child("type").valueAs<std::string>().c_str());
  if (!mat)
  