Normal map mask

I am using glass distortion shader from standard assets. I would like to apply mask to normal map, but i don’t know how. It’s easy to make a mask for texture, but i don’t know how to make it with normal maps. I could just apply a mask in external app like Gimp, but i want it to be applied at runtime, because i want to change normal map offset (animate it) without losing mask. I don’t want transparency but just applying black&white/transparent texture to normal map to make it flat in certain places.


  1. I have this normal map as input image: Click

  2. I use this image as mask: Click

  3. Generated normal map: Click

And then it just uses new normal map in output.

Here is a default shader: Click

Can anyone help mi with that?

First of all your “normal map” texture isn’t a normal map. It’s a bumpmap. However Unity doesn’t really use bumpmapping but normalmapping. The Unity editor usually converts imported bumpmaps into normalmaps. While a bumpmap is just a grayscale heightmap, a normal map contains actual normal vectors where each component of the vector is encoded in one of the color channels.

When a shader uses a normal map it will sample the normal map and use the unpacked vector as normal vector for lighting calculation. To “mask” a normal map at shader level you just need to do this in the fragment / surface shader:

  • grab the usual interpolated vertex normal (let’s call it “N”)
  • grab the unpacked sampled normal from the normal map (let’s call it “M”)
  • sample your “masking texture” to get a value between 0 and 1 (let’s call it “i”)
  • Lerp between “N” and “M” using “i”
  • normalize the result and use it as normal vector.

@miszelfox , did it work?
I am looking to make the same thing but I am not sure how to write it. do you have a sample code you can share?
Thank you