gecko/content/smil/nsSMILKeySpline.h

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 * The Original Code is the Mozilla SMIL module.
 *
 * The Initial Developer of the Original Code is Brian Birtles.
 * Portions created by the Initial Developer are Copyright (C) 2005
 * the Initial Developer. All Rights Reserved.
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 * Contributor(s):
 *   Brian Birtles <birtles@gmail.com>
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#ifndef NS_SMILKEYSPLINE_H_
#define NS_SMILKEYSPLINE_H_

#include "prtypes.h"

/**
 * Utility class to provide scaling defined in a keySplines element.
 */
class nsSMILKeySpline
{
public:
  /*
   * Create a new key spline control point description.
   *
   * aX1, etc. are the x1, y1, x2, y2 cubic Bezier control points as defined by
   * SMILANIM 3.2.3. They must each be in the range 0.0 <= x <= 1.0
   */
  nsSMILKeySpline(double aX1, double aY1,
                  double aX2, double aY2);

  /*
   * Get the output (y) value for an input (x).
   *
   * x should be a floating-point number between 0 and 1 (inclusive).
   */
  double GetSplineValue(double aX) const;

private:
  void
  CalcSampleValues();

  static double
  CalcBezier(double aT, double aA1, double aA2);

  static double
  GetSlope(double aT, double aA1, double aA2);

  double
  GetTForX(double aX) const;

  static double
  A(double aA1, double aA2)
  {
    return 1.0 - 3.0 * aA2 + 3.0 * aA1;
  }
  
  static double
  B(double aA1, double aA2)
  {
    return 3.0 * aA2 - 6.0 * aA1;
  }

  static double
  C(double aA1)
  {
    return 3.0 * aA1;
  }

  const double         mX1;
  const double         mY1;
  const double         mX2;
  const double         mY2;

  enum { kSplineTableSize = 11 };
  double               mSampleValues[kSplineTableSize];

  static const double  kSampleStepSize;
};

#endif // NS_SMILKEYSPLINE_H_