Make Bumpmapping Consistent with Displacement Mapping #285
Description
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.