Make Bumpmapping Consistent with Displacement Mapping

[devshgraphicsprogramming]

Describe the bug

Right now per-pixel derivative tangent frame calculation is invariant to UV or position scaling.

Bump ~~scale~~ height should be given relative to modelspace coordinates, i.e. a height of 1.0 should be 1-unit of modelspace coordinates.

Steps to Reproduce

Use Tessellation Shader or Parallax Occlusion Mapping to Displace a surface, compute the normal from per-pixel derivatives of the world space positions.

Compare computed normal with derivative map normal as given by nbl_glsl_perturb functions.

Expected vs observed behavior

Displacement mapped normal should be consistent with derivative map.

P.S. Also implement Schussler et. al, no one likes black crap in their derivative maps.

[devshgraphicsprogramming]

Schussler postponed.