Invisible Material for roofs for indoor simulation

[steffenitely]

Hi everybody ,
I want to do some indoor simulations and wanted to give my roof an invisible material so i can have a better overview of my scene when rendered. As suggested in the discussion "Adding Clip_at to render for indoor scenarios #398" i used a transparent BSDF for my invisible material and also tried to use a principled BSDF, but both did not result in an invisible roof/object. Is there a solution for this?

[merlinND]

Hello @steffenitely,

What do you see when calling scene.preview() with a clip_at argument? If you don't see any clipping happening, are you sure that you picked the right value? (it will depend on the scale of your scene along the vertical axis)

If using scene.render(), are you sure that the roofs have a null BSDF in the XML file that you load? What does the rendering look like?

[steffenitely]

Hi @merlinND
Thank you for the response! The clip_at argument works :) Though I was hoping i could use the null BSDF if i wanted more than one invisible wall or as in #398 when rendering the scene. The Transparent BSDF, when exported in blender to a XML file, turns into a Diffuse BSDF and the Principled BSDF turns into a twosided BSDF in the XML file. ith that i still see a solid coloured object. Does the Transparent BSDF work for you in a rendered scene when exported from Blender? If yes, maybe there is a problem with my Mitsuba add-on in Blender.
Otherwise, I will dig around in the Mitsuba BSDFs documentation to see if there is a way to create an invisible object by manualy changing the XML file after exporting it from Blender.
But im always open for more suggestions :)
Hope you have a good one!

EDIT: Changing the BSDF inside the XML to a null BSDF seems to work. Just like you suggested. Thanks again

[merlinND]

Does the Transparent BSDF work for you in a rendered scene when exported from Blender?

Actually you're right, the Blender exporter does not produce a null BSDF for Transparent materials. I got confused by looking at this importer code:

https://github.com/mitsuba-renderer/mitsuba-blender/blob/5a12adda2d0da3ccf3c125a54e36f7cf57988957/mitsuba-blender/io/importer/materials.py#L549-L551

The exporter doesn't map Transparent to null, probably because a tint can be added, which is not supported by null.