smith_neo_hookean_params.h

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 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
#pragma once
 
// PLEASE DO NOT ADD OTHER INCLUDES HERE. This header is included in the mochi_physics public API.
#include <mochi_core/materials/material_types.h>
#include <mochi_core/utils/reflection.h>
 
namespace superdex {
 
/**
 * @brief Parameters for the stable Neo-Hookean hyperelastic material model by Smith et al. (2018).
 *
 * @details Non-linear hyperelastic material with log-barrier stabilization to handle extreme
 * deformations and element inversions robustly. Recommended for most soft body simulations
 * requiring large deformations.
 *
 * @see [Stable Neo-Hookean Flesh Simulation (Smith et al.,
 * 2018)](https://www.tkim.graphics/NEO/StableNeoHookean2018.pdf)
 * @see SoftMaterialType::NeoHookean
 */
struct SmithNeoHookeanMaterialParams {
  /** @brief Young's modulus [Pa]. Must be positive. */
  real youngsModulus = kDefaultYoungsModulus;
 
  /**
   * @brief Poisson's ratio (dimensionless).
   *
   * @note Must be in (-1, 0.5). Near 0.5 = nearly incompressible.
   */
  real poissonRatio = kDefaultPoissonRatio;
 
  /**
   * @brief Strategy for ensuring positive semi-definite Hessian matrices.
   *
   * @see MaterialPsdStrategy
   */
  MaterialPsdStrategy psdStrategy = MaterialPsdStrategy::Projection;
 
#if MOCHI_LANGUAGE_CPP20
  bool operator==(SmithNeoHookeanMaterialParams const&) const = default;
#endif
 
  MOCHI_STRUCT_BEGIN(superdex::SmithNeoHookeanMaterialParams)
  MOCHI_FIELD(youngsModulus) MOCHI_ATTRIBUTE(Units("Pa"));
  MOCHI_FIELD(poissonRatio)
  MOCHI_FIELD(psdStrategy)
  MOCHI_STRUCT_END()
};
 
namespace materials {
// Neo-Hookean (Smith) has an isotropic reference tangent by construction.
template <>
inline constexpr bool kIsotropicReferenceStiffness<SmithNeoHookeanMaterialParams> = true;
} // namespace materials
 
} // namespace superdex