patch.cpp

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/* SPDX-FileCopyrightText: 2011-2022 Blender Foundation
 *
 * SPDX-License-Identifier: Apache-2.0 */
 
/* Parts adapted from code in the public domain in NVidia Mesh Tools. */
 
#include "subd/patch.h"
 
#include "util/math.h"
#include "util/types.h"
 
CCL_NAMESPACE_BEGIN
 
/* De Casteljau Evaluation */
 
static void decasteljau_cubic(float3 *P, float3 *dt, const float t, const float3 cp[4])
{
  float3 d0 = cp[0] + t * (cp[1] - cp[0]);
  float3 d1 = cp[1] + t * (cp[2] - cp[1]);
  const float3 d2 = cp[2] + t * (cp[3] - cp[2]);
 
  d0 += t * (d1 - d0);
  d1 += t * (d2 - d1);
 
  *P = d0 + t * (d1 - d0);
  if (dt) {
    *dt = d1 - d0;
  }
}
 
static void decasteljau_bicubic(
    float3 *P, float3 *du, float3 *dv, const float3 cp[16], float u, const float v)
{
  float3 ucp[4];
  float3 utn[4];
 
  /* interpolate over u */
  decasteljau_cubic(ucp + 0, utn + 0, u, cp);
  decasteljau_cubic(ucp + 1, utn + 1, u, cp + 4);
  decasteljau_cubic(ucp + 2, utn + 2, u, cp + 8);
  decasteljau_cubic(ucp + 3, utn + 3, u, cp + 12);
 
  /* interpolate over v */
  decasteljau_cubic(P, dv, v, ucp);
  if (du) {
    decasteljau_cubic(du, nullptr, v, utn);
  }
}
 
/* Linear Quad Patch */
 
void LinearQuadPatch::eval(
    float3 *P, float3 *dPdu, float3 *dPdv, float3 *N, const float u, float v) const
{
  const float3 d0 = interp(hull[0], hull[1], u);
  const float3 d1 = interp(hull[2], hull[3], u);
 
  *P = interp(d0, d1, v);
 
  if (N || (dPdu && dPdv)) {
    const float3 dPdu_ = interp(hull[1] - hull[0], hull[3] - hull[2], v);
    const float3 dPdv_ = interp(hull[2] - hull[0], hull[3] - hull[1], u);
 
    if (dPdu && dPdv) {
      *dPdu = dPdu_;
      *dPdv = dPdv_;
    }
 
    if (N) {
      *N = normalize(cross(dPdu_, dPdv_));
    }
  }
}
 
BoundBox LinearQuadPatch::bound()
{
  BoundBox bbox = BoundBox::empty;
 
  for (int i = 0; i < 4; i++) {
    bbox.grow(hull[i]);
  }
 
  return bbox;
}
 
/* Bicubic Patch */
 
void BicubicPatch::eval(
    float3 *P, float3 *dPdu, float3 *dPdv, float3 *N, const float u, const float v) const
{
  if (N) {
    float3 dPdu_;
    float3 dPdv_;
    decasteljau_bicubic(P, &dPdu_, &dPdv_, hull, u, v);
 
    if (dPdu && dPdv) {
      *dPdu = dPdu_;
      *dPdv = dPdv_;
    }
 
    *N = normalize(cross(dPdu_, dPdv_));
  }
  else {
    decasteljau_bicubic(P, dPdu, dPdv, hull, u, v);
  }
}
 
BoundBox BicubicPatch::bound()
{
  BoundBox bbox = BoundBox::empty;
 
  for (int i = 0; i < 16; i++) {
    bbox.grow(hull[i]);
  }
 
  return bbox;
}
 
CCL_NAMESPACE_END