I have a landscape material with 8 texture layers (+8 normals). How do you control the roughness and specular for each layer individually?
If it is all within one material, you can use lerp nodes to blend between the various textures to control how much of one drives the roughness. Typically you don’t really need to use the specular channel for PBR, just roughness and metalness.
I am really new to this type of material system. I just started using UE4 2 months ago. Would it be out of your way to post an image showing this in action?
PBR is also really new to me. Why is specular something that isn’t typically needed vs. metallic?
One option would be to put a roughness map in the alpha channel of your terrain textures and then wire the output alpha of your last layer node to the roughness slot. This would also be efficient in terms of texture lookups since you wouldn’t need an additional texture to control the roughness.
There is a forum post Physically Based Shading in UE4 - Announcements - Unreal Engine Forums which explains the principles of PBR pretty well. As a quick summary:
When light hits a surface, some of it is absorbed and some is reflected. Some of the absorbed light is re-emitted, but “tinted” by the material (which gives its color). Now, there are basically just two types of materials:
-
Metal (metalness=1). No absorption, just reflection (basically specularity=1.0)
-
Non-metal (metalness=0). Absorption and diffuse reflection, specularity around 0.04. Meaning, all non-metals have about the same amount of specularity.
The roughness controls if the light from the material is scattered in many directions (matte look) or not (glossy look). It is possibly the most important information in PBR. But there is no need for a specular map any more since this is basically defined by the metalness. You can of course still play around with it (and also with a metalness between 0 and 1) to create some unique look, but you’re slightly leaving the physical path there.
Aha. Thank you very much. You just explained something I have been wanting to know for awhile.
I have one last question; do you have a recommended method for producing a roughness mask? I am currently using the alpha of my terrain textures as alpha blending maps. I can apply the roughness masks to my normal maps. I am also wondering what the portion of the material will look like as I plug all the roughness masks in. I assume all the masks have to plug into one node that then plugs into the roughness input?