message: use opacity correction when sampling vkl intervals
diff: @@ -98,7 +98,9 @@ vec4f DRR_integrateVolumeInterval(const ScreenSample &sample,
  if (!isnan(sample)) {
  vec4f sampleColorOpacity = tf->get(tf, sample);
  - const float clampedOpacity = clamp(sampleColorOpacity.w * dt);
  + sampleColorOpacity.w = 1.f
  + - pow(1.f - sampleColorOpacity.w, dt / interval.nominalDeltaT);
  + const float clampedOpacity = clamp(sampleColorOpacity.w);
  color = color
  + ((1.f - alpha) * clampedOpacity
  * make_vec3f(sampleColorOpacity));
  