splinefunc.h

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#ifndef G3D_SPLINEFUNC_H
#define G3D_SPLINEFUNC_H

#include "G3D/platform.h"
#include "G3D/debug.h"
#include "G3D/Array.h"
#include "G3D/g3dmath.h"

namespace G3D {

template<class XType, class YType>
YType linearSpline(double x, const XType* controlX, const YType* controlY, int numControl) {
 debugAssert(numControl >= 1);

 // Off the beginning
 if ((numControl == 1) || (x < controlX[0])) {
 return controlY[0];
 }

 for (int i = 1; i < numControl; ++i) {
 if (x < controlX[i]) {
 const double alpha = (double)(controlX[i] - x) / (controlX[i] - controlX[i - 1]);
 return controlY[i] * (1 - alpha) + controlY[i - 1] * alpha;
 }
 }

 // Off the end
 return controlY[numControl - 1];
}

 
template<class YType> YType cyclicCatmullRomSpline(
 double t,
 const YType* controlY,
 int numPoints) {

 debugAssert(numPoints >= 3);

 t = wrap(t, numPoints);

 // Find the indices of adjacent control points 
 int i = iFloor(t);
 
 // Compute the distance from the control point
 t = t - i;

 // Shift back one point for correct indexing
 i += numPoints - 1;

 // Pick up four control points
 const YType& P0 = controlY[(i + 0) % numPoints];
 const YType& P1 = controlY[(i + 1) % numPoints];
 const YType& P2 = controlY[(i + 2) % numPoints];
 const YType& P3 = controlY[(i + 3) % numPoints];

 return 0.5 * ((2 * P1) + 
 (-P0 + P2) * t +
 (2*P0 - 5*P1 + 4*P2 - P3) * t*t +
 (-P0 + 3*P1- 3*P2 + P3) * t*t*t);
}

template<class YType> YType cyclicCatmullRomSpline(
 double t,
 const Array<YType>& controlY) {

 int numPoints = controlY.size();
 return cyclicCatmullRomSpline(t, controlY.getCArray(), numPoints);
}

}

#endif