message: show backplate in png if there
diff: @@ -149,12 +149,13 @@ void samplePath(const PathContext& pathContext,
  // backplate handling
  if (pathVertex.type == ENVIRONMENT && pathState.straightPath)
  {
  - sample.alpha = 1.0f - luminance(pathState.throughput);
  if ((bool)pathContext.context->backplate) {
  DifferentialGeometry lookup;
  initDgFromTexCoord(lookup, clamp2edge(pathContext.context->backplate, *pathContext.pixel));
  pathState.contribution = pathState.contribution + pathState.throughput * get3f(pathContext.context->backplate, lookup);
  }
  + else
  + sample.alpha = 1.0f - luminance(pathState.throughput);
  }
  if ((!pathState.disableFWD || pathState.depth == 0) && pathVertex.type != VOLUME) {
  