Make Object Visible/Opaque But Allow Light Through

[harry.anthony]

Hi!

I have a HDRI lighting my scene, but want to use a different background image for the region visible outside my window. I've put a plane outside covering the region and applied a self-illuminating material. Is there a way to allow the light from the HDRI to pass through this object whilst keeping the plane opaque, as I like the shadows cast by the HDRI? The plane object has Cast Shadows and Receive Illumination disabled but this doesn't seem to work.

Any help would be appreciated, and if there is a better way to change the background of the scene but keep the HDRI then please let me know! Thank you!

[10DSpace]

@harry.anthony 

I am not a Corona user, but from what I gather, Corona lights do not have a feature to exclude objects from lighting like some render engines do, but users have requested it .  See for example, 

https://forum.corona-renderer.com/index.php?topic=31342.0

https://forum.corona-renderer.com/index.php?topic=32156.0

I guess you have found out the Corona renderer also does not respect the Cast Shadows and Receive Illumination settings in the Max Object properties dialog.   

But have you tried adding another light outside the window (but in front of the image plane) to fake the direction of the HDRI lighting to get the shadows you want?  Corona may have a suitable light type to allow you to project the HDRI Image you are using as a light source.  Or maybe just a solid light color (to approximate average of HDRI image) with a directional light will look OK for the shadows. 

[harry.anthony]

Hi @10DSpace !

Thanks for the quick response!

I was not aware that Corona ignores Cast Shadows and Receive Illumination, but that explains why they weren’t acting as I expected. I have added an area/rectangle single colour light in front of the plane and hidden it, as you suggested, which is a good work around, the lighting is not exactly the same as the HDRI of course but it’s close enough with a bit of trial and error. When using the HDRI image as the light source the small scale gives unrealistic shadows in this instance.

Thank you for your help, it’s massively appreciated! Corona is typically pretty good at having work arounds, such as excluding/including specific objects for lights, but I guess not in this particular case.