SciBall.h

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/*
   For more information, please see: http://software.sci.utah.edu

   The MIT License

   Copyright (c) 2013 Scientific Computing and Imaging Institute,
   University of Utah.


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/// \author James Hughes
/// \date   April 2013

#ifndef SPIRE_APPSPECIFIC_SCIRUN_SCIBALL_H
#define SPIRE_APPSPECIFIC_SCIRUN_SCIBALL_H

#include <cstdint>

#include <Interface/Modules/Render/namespaces.h>

#include "spire/Interface.h"

namespace SCIRun {
namespace Gui {

/// A reimplementation of Ken Shoemake's arcball camera. SCIRun 4's camera
/// system is based off of Ken's code. The Code appears in Graphics Gems 4, 
/// III.1.
/// 
/// Unless specified otherwise, all calculations and variables stored in this
/// class are relative to the target coordinate system (TCS) for which there is
/// a transformation from screen space to TCS given by the screenToTCS
/// constructor parameter.
///
/// If the screenToTCS parameter in the constructor is left as the identity
/// matrix then all values are given in screen coordinates.
/// Screen coordinates are (x \in [-1,1]) and (y \in [-1,1]) where (0,0) is the
/// center of the screen.
/// \todo Extend this class to include Mouse screen coords -> object space
///       calculations. That way we can rotate around a particular object.
///       May also want to visually represent the sphere when we perform this
///       calculation.
/// \todo Provide method of setting the default orientation of the object.
class SciBall
{
public:
  /// \param center         Center of the arcball in TCS (screen coordinates if 
  ///                       screenToTCS = identity). Generally this will 
  ///                       always be (0,0,0). But you may move the center
  ///                       in and out of the screen plane to various effect.
  /// \param radius         Radius in TCS. For screen coordinates, a good
  ///                       default is 0.75.
  /// \param screenToTCS    Transformation from screen coordinates
  ///                       to TCS. 'center' and 'radius' are given in TCS.
  SciBall(const spire::V3& center, float radius,
          const spire::M44& screenToTCS = spire::M44());
  virtual ~SciBall();
  
  /// Initiate an arc ball drag given the mouse click in screen coordinates.
  /// \param mouseScreenCoords  Mouse screen coordinates.
  void beginDrag(const spire::V2& mouseScreenCoords);

  /// Informs the arcball when the mouse has been dragged.
  /// \param mouseScreenCoords  Mouse screen coordinates.
  void drag(const spire::V2& mouseScreenCoords);

  /// Retrieves the current transformation in TCS.
  /// Obtains full transformation of object in question. If the arc ball is 
  /// being used to control camera rotation, then this will contain all
  /// concatenated camera transformations. The current state of the camera
  /// is stored in the quaternions mQDown and mQNow. mMatNow is calculated
  /// from mQNow.
  spire::M44 getTransformation() const;

private:

  /// Calculates our position on the ArcBall from 2D mouse position.
  /// \param tscMouse   TSC coordinates of mouse click.
  spire::V3 mouseOnSphere(const spire::V3& tscMouse);

  /// Construct a unit quaternion from two points on the unit sphere.
  static spire::Quat quatFromUnitSphere(const spire::V3& from, const spire::V3& to);

  spire::V3   mCenter;        ///< Center of the arcball in target coordinate system.
  float       mRadius;        ///< Radius of the arcball in target coordinate system.

  /// \note Both mQNow and mQDown would need to be updated if we allowed
  ///       default transformations.

  spire::Quat mQNow;          ///< Current state of the rotation taking into account mouse.
                              ///< Essentially QDrag * QDown (QDown is a applied first, just
                              ///< as in matrix multiplication).
  spire::Quat mQDown;         ///< State of the rotation since mouse down.
  spire::Quat mQDrag;         ///< Dragged transform. Knows nothing of any prior 
                              ///< transformations.

  spire::V3   mVNow;          ///< Most current TCS position of mouse (during drag).
  spire::V3   mVDown;         ///< TCS position of mouse when the drag was begun.
  spire::V3   mVSphereFrom;   ///< vDown mapped to the sphere of 'mRadius' centered at 'mCenter' in TCS.
  spire::V3   mVSphereTo;     ///< vNow mapped to the sphere of 'mRadius' centered at 'mCenter' in TCS.

  spire::M44  mMatNow;        ///< Matrix representing the current rotation.

  /// \todo Add in constraint sets (you can display handles and constrain
  ///       rotations along those handles).

  /// Transform from screen coordinates to the target coordinate system.
  spire::M44  mScreenToTCS;
};

} // namespace Gui
} // namespace SCIRun 

#endif