Vertex displace with flat shading

Hello all,
maybe someone could give me a hint how to achieve flat shading for a mesh when vertices are displaced in vertexshader by a texture?

For smooth lighting, i know 2 ways: 1st like in displacement shader heightmap-displacement, and another one i’ve learned from Dottore particles library’s bicubic surface, where normals are calculated in vertexshader.

But is there a way to calculate same normals for each face (from vertex positions) and get them in PS for flat look?

thx for any help

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Flat Shading in (3.4 kB)