Reflect on back side only works with 1.0 glossiness for GGX and Phong

[1funk]

I've been trying to figure out why "reflect on back side" has not been working after following a tutorial.

I was using GGX and it seems "reflect on back side", only works if glossiness = 1.0. The same problem happens with phong too. Blinn and Ward allow other values while keeping the reflections on the back side visible.

Modo 11.0 138707
V-Ray 3.52.01 27378

Top has glossiness 1.0. You can see the reflections on the back side of polygons. The bottom has glossiness at 0.99 and the back facing reflections vanish.

EDIT: Updated scene - enabling glossy fresnel. With this option enabled, Blinn and Ward seem to work with glossiness less than 1.0

[boyan]

Howdy Funk,

Thank for the post. Well, I've added the issue to the system. Keep you posted about it.

Meanwhile, you can try to use texture map assigned it to reflection glossiness slot. Is this workable for you?



Cheers,

[1funk]

Thanks Boyan. I just tested using a texture and it doesnt work either. Maybe my example isnt clear?

Please reload my original scene, then set "mat 1" reflection glossiness to 0.99 and back to 1.0 to see the difference. You will noticed the deeper blue reflections (behind the front "white" reflection) go away.

Using a texture with a value of 0.99 will do the same thing

EDIT: I have attached an image with an A/B split which shows it clearer

[1funk]

I wanted to leave a note here. It seems this problem also happens using Blinn and Ward BRDFs. I'm not sure how I missed that

[1funk]

A little more info. If "glossy fresnel" is enabled, Blinn and Ward BRDF work with glossiness less than 1.0

I had this enabled in my original scene, but didnt enable it in the example I uploaded here. I have uploaded an updated scene