message: Fixed cases where transmission depth = 0.  Was producing wrong color.
diff: -// Copyright 2009-2019 Intel Corporation
  +// Copyright 2009-2020 Intel Corporation
  // SPDX-License-Identifier: Apache-2.0
  #include "../bsdfs/Conductor.ih"
  @@ -289,10 +289,13 @@ const varying BSDF *varying Principled_getBSDF(
  // thin
  const vec3f transmissionColor = clamp(self->transmissionColor
  * get3f(self->transmissionColorMap, dg, make_vec3f(1.f)));
  + const float transmissionDepth = max(self->transmissionDepth
  + * get1f(self->transmissionDepthMap, dg, 1.f),
  + EPS);
  const float thickness =
  max(self->thickness * get1f(self->thicknessMap, dg, 1.f), 0.f);
  const vec3f attenuation =
  - logf(transmissionColor) / self->transmissionDepth * thickness;
  + logf(transmissionColor) / transmissionDepth * thickness;
  if (roughness < EPS)
  glassBsdf =
  @@ -468,7 +471,7 @@ vec3f Principled_getTransparency(
  * get3f(self->transmissionColorMap, dg, make_vec3f(1.f)));
  const float transmissionDepth = max(self->transmissionDepth
  * get1f(self->transmissionDepthMap, dg, 1.f),
  - 0.f);
  + EPS);
  const float thickness =
  max(self->thickness * get1f(self->thicknessMap, dg, 1.f), 0.f);
  const vec3f attenuation =
  @@ -565,7 +568,7 @@ void Principled_selectNextMedium(const uniform PathTraceMaterial *uniform super,
  * get3f(self->transmissionColorMap, dg, make_vec3f(1.f)));
  const float transmissionDepth = max(
  self->transmissionDepth * get1f(self->transmissionDepthMap, dg, 1.f),
  - 0.f);
  + EPS);
  currentMedium.ior = ior;
  currentMedium.attenuation = logf(transmissionColor) / transmissionDepth;
  