How do you use IRO for opaque materials?

cturbo

Hello! I've been informed about the use of the index of refraction for opaque materials such as brick, and I'm curious about how they apply it in Unreal for opaque materials. Should I configure it with the same settings as glass, like using Translucent and fast forward shading? I haven't come across many tutorials on this topic, so any advice would be greatly appreciated!

Eric Chadwick

The abbreviation is IOR, and in real-time 3d rendering it is mostly used for refractive materials like glass, water, transparent plastic, gems, etc. 

But you can also use it to force reflectivity to be stronger... we used to use high IOR values (anything over 5) to make materials look metallic, before there was the PBR metallic-roughness material model. But now with PBR we just use the metallic parameter (or texture) instead, because it's simpler and it's also more physically accurate.

IOR for brick would be very low. In real-time rendering of non-transparent non-metallic surfaces, the higher the IOR the more reflectivity you see on surfaces facing the camera.

Eric Chadwick

You can read more here about how IOR fits into the whole shading system:
https://www.adobe.com/learn/substance-3d-designer/web/the-pbr-guide-part-1

However this doc isn't really written with artists in mind, unless they're already pretty technically-inclined. It's written more for graphics engineers. But you should still be able to get some good info from it!

cturbo

Thank you once more, Eric, for all that helpful information! Do you still use IOR for your materials, or have you switched to metallic since PBR? I'm also trying to achieve a nice brick color. I made one in Substance Designer and sampled colors from a photo using a gradient, but it never seems to look quite realistic. Do you have any advice on how to get color swatches for bricks? I've seen others taking pictures of bricks and using them as texture maps, and I was wondering if that's the best approach for coloring bricKs? My bricks also look flat in unreal, and wondered what you do to give your bricks some height?

poopipe

specular reflectance  is equivalent to IOR for our purposes so you're using it either way. 

for a metallic roughness model:
- on metallic surfaces it's a function of metalness value and basecolor
- on non-metals it's either equivalent to acrylic/paint or defined by a separate texture (dielectric specular level - or just specular in unreal)

in simple terms the result affects how strong reflection is at a given view angle.
in slightly less simple terms...
all surfaces are infinitely reflective when the view angle is parallel to the surface and the specular reflectance value basically defines how much that falls off as you reach a perpendicular view angle

Eric Chadwick

Yeah… but BRICKS!

cturbo, we need screenshots, otherwise we can’t help. What does it look like lit, and what do each of the textures look like?

cturbo

Eric Chadwick said:

Yeah… but BRICKS!

cturbo, we need screenshots, otherwise we can’t help. What does it look like lit, and what do each of the textures look like?

I'm still far from getting the brick look I desire. I've been playing around with the height map because I couldn't figure out why it looks so flat in Unreal but not in Substance Designer. If I want to incorporate a specular, what value should I set for bricks? Additionally, I would be grateful for any tips on how to achieve this specific brick color. The building I'm referencing has a black brick hue, not the light white brick you see at the top, and these are Georgian bricks as well. I took some photos with my iPhone, but they're not in raw format, just JPGs, which I've heard can complicate color separation. I keep getting a lot of muted colors when I use the color picker.

Axi5

First thing I notice is that your specular is at 1.0, it should probably be at 0.5, IIRC it's typically a scale from 0-8% reflectivity with 0.5 being 4% which is approximately correct for most non-metallic materials.

cturbo

Axi5 said:

First thing I notice is that your specular is at 1.0, it should probably be at 0.5, IIRC it's typically a scale from 0-8% reflectivity with 0.5 being 4% which is approximately correct for most non-metallic materials.

Thanks for the tip, do you know any good realistic brick tutorials i can follow along to?