/* SPDX-License-Identifier: Apache-2.0
 * Copyright 2011-2022 Blender Foundation */

#include "stdcycles.h"

/* "Bump Mapping Unparameterized Surfaces on the GPU"
 * Morten S. Mikkelsen, 2010 */

surface node_bump(int invert = 0,
                  int use_object_space = 0,
                  normal NormalIn = N,
                  float Strength = 0.1,
                  float Distance = 1.0,
                  float SampleCenter = 0.0,
                  float SampleX = 0.0,
                  float SampleY = 0.0,
                  output normal NormalOut = N)
{
  point Ptmp = P;
  normal Normal = NormalIn;

  if (use_object_space) {
    Ptmp = transform("object", Ptmp);
    Normal = normalize(transform("object", Normal));
  }

  /* get surface tangents from normal */
  vector dPdx = Dx(Ptmp);
  vector dPdy = Dy(Ptmp);

  vector Rx = cross(dPdy, Normal);
  vector Ry = cross(Normal, dPdx);

  /* compute surface gradient and determinant */
  float det = dot(dPdx, Rx);
  vector surfgrad = (SampleX - SampleCenter) * Rx + (SampleY - SampleCenter) * Ry;

  float absdet = fabs(det);

  float strength = max(Strength, 0.0);
  float dist = Distance;

  if (invert)
    dist *= -1.0;

  /* compute and output perturbed normal */
  NormalOut = normalize(absdet * Normal - dist * sign(det) * surfgrad);
  NormalOut = normalize(strength * NormalOut + (1.0 - strength) * Normal);

  if (use_object_space) {
    NormalOut = normalize(transform("object", "world", NormalOut));
  }

  NormalOut = ensure_valid_reflection(Ng, I, NormalOut);
}