AnimTestbed/3rdparty/ozz-animation/include/ozz/animation/runtime/ik_two_bone_job.h

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#ifndef OZZ_OZZ_ANIMATION_RUNTIME_IK_TWO_BONE_JOB_H_
#define OZZ_OZZ_ANIMATION_RUNTIME_IK_TWO_BONE_JOB_H_

#include "ozz/base/platform.h"

#include "ozz/base/maths/simd_math.h"

namespace ozz {
// Forward declaration of math structures.
namespace math {
struct SimdQuaternion;
}

namespace animation {

// ozz::animation::IKTwoBoneJob performs inverse kinematic on a three joints
// chain (two bones).
// The job computes the transformations (rotations) that needs to be applied to
// the first two joints of the chain (named start and middle joints) such that
// the third joint (named end) reaches the provided target position (if
// possible). The job outputs start and middle joint rotation corrections as
// quaternions.
// The three joints must be ancestors, but don't need to be direct
// ancestors (joints in-between will simply remain fixed).
// Implementation is inspired by Autodesk Maya 2 bone IK, improved stability
// wise and extended with Soften IK.
struct IKTwoBoneJob {
  // Constructor, initializes default values.
  IKTwoBoneJob();

  // Validates job parameters. Returns true for a valid job, or false otherwise:
  // -if any input pointer is nullptr
  // -if mid_axis isn't normalized.
  bool Validate() const;

  // Runs job's execution task.
  // The job is validated before any operation is performed, see Validate() for
  // more details.
  // Returns false if *this job is not valid.
  bool Run() const;

  // Job input.

  // Target IK position, in model-space. This is the position the end of the
  // joint chain will try to reach.
  math::SimdFloat4 target;

  // Normalized middle joint rotation axis, in middle joint local-space. Default
  // value is z axis. This axis is usually fixed for a given skeleton (as it's
  // in middle joint space). Its direction is defined like this: a positive
  // rotation around this axis will open the angle between the two bones. This
  // in turn also to define which side the two joints must bend. Job validation
  // will fail if mid_axis isn't normalized.
  math::SimdFloat4 mid_axis;

  // Pole vector, in model-space. The pole vector defines the direction the
  // middle joint should point to, allowing to control IK chain orientation.
  // Note that IK chain orientation will flip when target vector and the pole
  // vector are aligned/crossing each other. It's caller responsibility to
  // ensure that this doesn't happen.
  math::SimdFloat4 pole_vector;

  // Twist_angle rotates IK chain around the vector define by start-to-target
  // vector. Default is 0.
  float twist_angle;

  // Soften ratio allows the chain to gradually fall behind the target
  // position. This prevents the joint chain from snapping into the final
  // position, softening the final degrees before the joint chain becomes flat.
  // This ratio represents the distance to the end, from which softening is
  // starting.
  float soften;

  // Weight given to the IK correction clamped in range [0,1]. This allows to
  // blend / interpolate from no IK applied (0 weight) to full IK (1).
  float weight;

  // Model-space matrices of the start, middle and end joints of the chain.
  // The 3 joints should be ancestors. They don't need to be direct
  // ancestors though.
  const math::Float4x4* start_joint;
  const math::Float4x4* mid_joint;
  const math::Float4x4* end_joint;

  // Job output.

  // Local-space corrections to apply to start and middle joints in order for
  // end joint to reach target position.
  // These quaternions must be multiplied to the local-space quaternion of their
  // respective joints.
  math::SimdQuaternion* start_joint_correction;
  math::SimdQuaternion* mid_joint_correction;

  // Optional boolean output value, set to true if target can be reached with IK
  // computations. Reachability is driven by bone chain length, soften ratio and
  // target distance. Target is considered unreached if weight is less than 1.
  bool* reached;
};
}  // namespace animation
}  // namespace ozz
#endif  // OZZ_OZZ_ANIMATION_RUNTIME_IK_TWO_BONE_JOB_H_