Question Will it be good way to combine 2 normalmaps?

(For situations when I cannot pre- combine them in 2d editor (procedural content)). So, I thought about applying effects of both normals consecutively. 1)Unpack the first map with standard algorithm 2)Align tangent and binormal to new normal vector using cross products 3)Custom unpack the second map (get it to -1/1 space, scale new coordinate vectors by xyz components, sum vectors). Will it be unacceptably slow? Or wrong algorithm completely?

 

You want to blend them in tangent space if you can.
https://blog.selfshadow.com/publications/blending-in-detail/

I have a version of the RNM function modified to work well with Unity’s shaders here:
https://github.com/bgolus/Normal-Mapping-for-a-Triplanar-Shader/blob/master/TriplanarRNM.shader

 

I'll go study it, thank you. I think I even seen some your articles couple of years ago when I tried to make triplanar shader for Blender. Copied the whiteout blend formula mindlessly and it worked.