shape_specification.h

#pragma once

#include <functional>
#include <memory>
#include <string>
#include <typeindex>

#include "drake/common/drake_assert.h"
#include "drake/common/drake_copyable.h"
#include "drake/common/drake_deprecated.h"
#include "drake/common/eigen_types.h"
#include "drake/math/rigid_transform.h"

/** @file
 Provides the classes through which geometric shapes are introduced into
 SceneGraph. This includes the specific classes which specify shapes as well
 as an interface for _processing_ those specifications.
 */

namespace drake {
namespace geometry {

class ShapeReifier;

/** Simple struct for instantiating the type-specific Shape functionality.
 A class derived from the Shape class will invoke the parent's constructor as
 Shape(ShapeTag<DerivedShape>()). */
template <typename ShapeType>
struct ShapeTag{};

/** The base interface for all shape specifications. It has no public
  constructor and cannot be instantiated directly. The Shape class has two
  key properties:

   - it is cloneable, and
   - it can be "reified" (see ShapeReifier).

  When you add a new subclass of Shape, you must:

  1. add a virtual function ImplementGeometry() for the new shape in
     ShapeReifier that invokes the ThrowUnsupportedGeometry method, and add to
     the test for it in shape_specification_test.cc.
  2. implement ImplementGeometry in derived ShapeReifiers to continue support
     if desired, otherwise ensure unimplemented functions are not hidden in new
     derivations of ShapeReifier with `using`, for example, `using
     ShapeReifier::ImplementGeometry`. Existing subclasses should already have
     this.

  Otherwise, you might get a runtime error. We do not have an automatic way to
  enforce them at compile time.
 */
class Shape {
 public:
  virtual ~Shape();

  /** Causes this description to be reified in the given `reifier`. Each
   concrete subclass must invoke the single, matching method on the reifier.
   Provides optional user-data (cast as a void*) for the reifier to consume. */
  void Reify(ShapeReifier* reifier, void* user_data = nullptr) const;

  /** Creates a unique copy of this shape. */
  std::unique_ptr<Shape> Clone() const;

 protected:
  // This is *not* in the public section. However, this allows the children to
  // also use this macro, but precludes the possibility of external users
  // slicing Shapes.
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Shape)

  /** Constructor available for derived class construction. A derived class
   should invoke this in its initialization list, passing a ShapeTag
   instantiated on its derived type, e.g.:

   ```
   class MyShape final : public Shape {
    public:
     MyShape() : Shape(ShapeTag<MyShape>()) {}
     ...
   };
   ```

   The base class provides infrastructure for cloning and reification. To work
   and to maintain sanity, we place the following requirements on derived
   classes:

   1. they must have a public copy constructor,
   2. they must be marked as final, and
   3. their constructors must invoke the parent constructor with a ShapeTag
      instance (as noted above), and
   4. The ShapeReifier class must be extended to include an invocation of
      ShapeReifier::ImplementGeometry() on the derived Shape class.

   @tparam S    The derived shape class. It must derive from Shape. */
  template <typename S>
  explicit Shape(ShapeTag<S> tag);

 private:
  std::function<std::unique_ptr<Shape>(const Shape&)> cloner_;
  std::function<void(const Shape&, ShapeReifier*, void*)> reifier_;
};

/** Definition of sphere. It is centered in its canonical frame with the
 given radius. */
class Sphere final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Sphere)

  /** Constructs a sphere with the given `radius`.
   @throws std::exception if `radius` is negative. Note that a zero radius is
   is considered valid. */
  explicit Sphere(double radius);

  double radius() const { return radius_; }

 private:
  double radius_{};
};

/** Definition of a cylinder. It is centered in its canonical frame with the
 length of the cylinder parallel with the frame's z-axis. */
class Cylinder final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Cylinder)

  /** Constructs a cylinder with the given `radius` and `length`.
   @throws std::exception if `radius` or `length` are not strictly positive.
   */
  Cylinder(double radius, double length);

  double radius() const { return radius_; }
  double length() const { return length_; }

 private:
  double radius_{};
  double length_{};
};

/** Definition of a box. The box is centered on the origin of its canonical
 frame with its dimensions aligned with the frame's axes. The size of the box
 is given by three sizes. */
class Box final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Box)

  /** Constructs a box with the given `width`, `depth`, and `height`, which
   specify the box's dimension along the canonical x-, y-, and z-axes,
   respectively.
   @throws std::exception if `width`, `depth` or `height` are not strictly
   positive. */
  Box(double width, double depth, double height);

  /** Constructs a cube with the given `edge_size` for its width, depth, and
   height. */
  static Box MakeCube(double edge_size);

  /** Returns the box's dimension along the x axis. */
  double width() const { return size_(0); }

  /** Returns the box's dimension along the y axis. */
  double depth() const { return size_(1); }

  /** Returns the box's dimension along the z axis. */
  double height() const { return size_(2); }

  /** Returns the box's dimensions. */
  const Vector3<double>& size() const { return size_; }

 private:
  Vector3<double> size_;
};

/** Definition of a capsule. The capsule can be thought of as a cylinder with
 spherical caps attached. The capsule's length refers to the length of the
 cylindrical region, and the radius applies to both the cylinder and spherical
 caps. A capsule with zero length is a sphere of the given radius. And a capsule
 with zero radius is a line segment with the given length. The capsule is
 defined in its canonical frame C, centered on the frame origin and with the
 length of the capsule parallel with the frame's z-axis. */
class Capsule final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Capsule)

  /** Constructs a capsule with the given `radius` and `length`.
   @throws std::exception if `radius` or `length` are not strictly positive.
   */
  Capsule(double radius, double length);

  double radius() const { return radius_; }
  double length() const { return length_; }

 private:
  double radius_{};
  double length_{};
};

/** Definition of an ellipsoid. It is centered on the origin of its canonical
 frame with its dimensions aligned with the frame's axes. The standard
 equation for the ellipsoid is:

          x²/a² + y²/b² + z²/c² = 1,
 where a,b,c are the lengths of the principal semi-axes of the ellipsoid.
 The bounding box of the ellipsoid is [-a,a]x[-b,b]x[-c,c].
*/
class Ellipsoid final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Ellipsoid)

  /** Constructs an ellipsoid with the given lengths of its principal
   semi-axes.
   @throws std::exception if `a`, `b`, or `c` are not strictly positive.
   */
  Ellipsoid(double a, double b, double c);

  double a() const { return radii_(0); }
  double b() const { return radii_(1); }
  double c() const { return radii_(2); }

 private:
  Vector3<double> radii_;
};

/** Definition of a half space. In its canonical frame, the plane defining the
 boundary of the half space is that frame's z = 0 plane. By implication, the
 plane's normal points in the +z direction and the origin lies on the plane.
 Other shapes are considered to be penetrating the half space if there exists
 a point on the test shape that lies on the side of the plane opposite the
 normal. */
class HalfSpace final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(HalfSpace)

  HalfSpace();

  /** Creates the pose of a canonical half space in frame F.
   The half space's normal is aligned to the positive z-axis of its canonical
   frame H. Given a vector that points in the same direction, measured in the
   F frame (Hz_dir_F) and a position vector to a point on the half space's
   *boundary* expressed in the same frame, `p_FB`, creates
   the pose of the half space in frame F: `X_FH`.
   @param Hz_dir_F  A vector in the direction of the positive z-axis of the
                    canonical frame expressed in frame F. It must be a non-zero
                    vector but need not be unit length.
   @param p_FB      A point B lying on the half space's boundary measured
                    and expressed in frame F.
   @retval X_FH     The pose of the canonical half-space in frame F.
   @throws std::exception if the normal is _close_ to a zero-vector (e.g.,
                          ‖normal_F‖₂ < ε). */
  static math::RigidTransform<double> MakePose(const Vector3<double>& Hz_dir_F,
                                               const Vector3<double>& p_FB);
};

// TODO(DamrongGuoy): Update documentation when the level of support for
//  meshes extends to more collision and rendering.
/** Limited support for meshes. Meshes are supported in Rendering and
 Illustration roles. For Proximity role, Meshes are supported in
 ComputeContactSurfaces() query only. No other proximity queries are supported.
 */
class Mesh final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Mesh)

  /** Constructs a mesh specification from the mesh file located at the given
   _absolute_ file path. Optionally uniformly scaled by the given scale factor.
   @throws std::exception if |scale| < 1e-8. Note that a negative scale is
   considered valid. We want to preclude scales near zero but recognise that
   scale is a convenience tool for "tweaking" models. 8 orders of magnitude
   should be plenty without considering revisiting the model itself. */
  explicit Mesh(const std::string& absolute_filename, double scale = 1.0);

  const std::string& filename() const { return filename_; }
  double scale() const { return scale_; }

 private:
  // NOTE: Cannot be const to support default copy/move semantics.
  std::string filename_;
  double scale_;
};

/** Support for convex shapes. */
class Convex final : public Shape {
 public:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(Convex)

  /** Constructs a convex shape specification from the file located at the
   given _absolute_ file path. Optionally uniformly scaled by the given scale
   factor.
   @param absolute_filename     The file name with absolute path. We only
                                support an .obj file with only one polyhedron.
                                We assume that the polyhedron is convex.
   @param scale                 An optional scale to coordinates.

   @throws std::exception       if the .obj file doesn't define a single object.
                                This can happen if it is empty, if there are
                                multiple object-name statements (e.g.,
                                "o object_name"), or if there are faces defined
                                outside a single object-name statement.
   @throws std::exception       if |scale| < 1e-8. Note that a negative scale is
                                considered valid. We want to preclude scales
                                near zero but recognise that scale is a
                                convenience tool for "tweaking" models. 8 orders
                                of magnitude should be plenty without
                                considering revisiting the model itself. */
  explicit Convex(const std::string& absolute_filename, double scale = 1.0);

  const std::string& filename() const { return filename_; }
  double scale() const { return scale_; }

 private:
  std::string filename_;
  double scale_;
};

/** The interface for converting shape descriptions to real shapes. Any entity
 that consumes shape descriptions _must_ implement this interface.

 This class explicitly enumerates all concrete shapes in its methods. The
 addition of a new concrete shape class requires the addition of a new
 corresponding method. There should *never* be a method that accepts the Shape
 base class as an argument; it should _only_ operate on concrete derived
 classes.

 The expected workflow is for a class that needs to turn shape specifications
 into concrete geometry instances to implement the %ShapeReifier interface
 _and_ invoke the Shape::Reify() method. For example, a simple reifier that
 requires no user data would look like:

 ```
 class SimpleReifier : public ShapeReifier {
   void ProcessShape(const Shape& shape) {
     // Requires no user data.
     shape.Reify(this);
   }
   ...
   void ImplementGeometry(const Sphere& sphere, void*) override {
     // Do work to create a sphere.
   }
 };
 ```

 Or a complex reifier that requires user data would look like:

 ```
 class ComplexReifier : public ShapeReifier {
   void ProcessShape(const Shape& shape) {
     ImportantData data{...};
     shape.Reify(this, &data);
   }
   ...
   void ImplementGeometry(const Sphere& sphere, void* data) override {
     DRAKE_ASSERT(data);
     ImportantData& data = *static_cast<ImportantData*>(data);
     // Do work to create a sphere using the provided user data.
   }
 };
 ```

 Implementing a particular shape may require more data than is strictly
 encapsulated in the Shape. The Implement* interface supports passing user
 data through a type-erased `void*`. Because a single class invoked
 Shape::Reify() it is in a position to provide exactly the data the shape
 implementations require.  */
class ShapeReifier {
 public:
  virtual ~ShapeReifier() = default;

  virtual void ImplementGeometry(const Sphere& sphere, void* user_data);
  virtual void ImplementGeometry(const Cylinder& cylinder, void* user_data);
  virtual void ImplementGeometry(const HalfSpace& half_space, void* user_data);
  virtual void ImplementGeometry(const Box& box, void* user_data);
  virtual void ImplementGeometry(const Capsule& capsule, void* user_data);
  virtual void ImplementGeometry(const Ellipsoid& ellipsoid, void* user_data);
  virtual void ImplementGeometry(const Mesh& mesh, void* user_data);
  virtual void ImplementGeometry(const Convex& convex, void* user_data);

 protected:
  DRAKE_DEFAULT_COPY_AND_MOVE_AND_ASSIGN(ShapeReifier)
  ShapeReifier() = default;

  /** Derived ShapeReifiers can replace the default message for unsupported
   geometries by overriding this method. The name of the unsupported shape type
   is given as the single parameter.  */
  virtual void ThrowUnsupportedGeometry(const std::string& shape_name);
};

template <typename S>
Shape::Shape(ShapeTag<S>) {
  static_assert(std::is_base_of_v<Shape, S>,
                "Concrete shapes *must* be derived from the Shape class");
  cloner_ = [](const Shape& shape_arg) {
    DRAKE_DEMAND(typeid(shape_arg) == typeid(S));
    const S& derived_shape = static_cast<const S&>(shape_arg);
    return std::unique_ptr<Shape>(new S(derived_shape));
  };
  reifier_ = [](const Shape& shape_arg, ShapeReifier* reifier,
                void* user_data) {
    DRAKE_DEMAND(typeid(shape_arg) == typeid(S));
    const S& derived_shape = static_cast<const S&>(shape_arg);
    reifier->ImplementGeometry(derived_shape, user_data);
  };
}

// TODO(SeanCurtis-TRI): Merge this into shape_to_string.h so that there's a
//  single utility for getting a string from a shape.
/** Class that reports the name of the type of shape being reified (e.g.,
 Sphere, Box, etc.)  */
class ShapeName final : public ShapeReifier {
 public:
  ShapeName() = default;

  /** Constructs a %ShapeName from the given `shape` such that `string()`
   already contains the string representation of `shape`.  */
  explicit ShapeName(const Shape& shape) {
    shape.Reify(this);
  }

  /** @name  Implementation of ShapeReifier interface  */
  //@{

  using ShapeReifier::ImplementGeometry;

  void ImplementGeometry(const Sphere&, void*) final {
    string_ = "Sphere";
  }
  void ImplementGeometry(const Cylinder&, void*) final {
    string_ = "Cylinder";
  }
  void ImplementGeometry(const HalfSpace&, void*) final {
    string_ = "HalfSpace";
  }
  void ImplementGeometry(const Box&, void*) final {
    string_ = "Box";
  }
  void ImplementGeometry(const Capsule&, void*) final {
    string_ = "Capsule";
  }
  void ImplementGeometry(const Ellipsoid&, void*) final {
    string_ = "Ellipsoid";
  }
  void ImplementGeometry(const Mesh&, void*) final {
    string_ = "Mesh";
  }
  void ImplementGeometry(const Convex&, void*) final {
    string_ = "Convex";
  }

  //@}

  /** Returns the name of the last shape reified. Empty if no shape has been
   reified yet.  */
  std::string name() const { return string_; }

 private:
  std::string string_;
};

/** @relates ShapeName */
std::ostream& operator<<(std::ostream& out, const ShapeName& name);

}  // namespace geometry
}  // namespace drake