lerp.cpp

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#include "lerp.h"

Transformation linear_interpolate_uncapped( const Transformation &A, const Transformation &B, double blend )
{
    Quaternion result;
    if (0 /*A.orientation==B.orientation*/) {
        result = A.orientation;
    } else {
        const Quaternion &a = A.orientation;
        const Quaternion &b = B.orientation;
        double     f = blend, f0, f1, sadj=1;
        double     cos_omega = DotProduct( a.v, b.v )+a.s*b.s;
        //Adjust signs if necessary.
        if (cos_omega < 0) {
            cos_omega = -cos_omega;
            sadj = -1;
        }
        if (cos_omega < 0.99) {
            //Do the spherical interp.
            double omega     = acos( cos_omega );
            double isin_omega = 1.0 / sin( omega );
            f0 = sin( (1-f)*omega ) * isin_omega;
            f1 = sin( f*omega ) * isin_omega;
        } else {
            //Quaternions are close; just do straight lerp and avoid division by near-zero.
            f0 = 1-f;
            f1 = f;
        }
        result.s = a.s*float(f0)+b.s*float(f1*sadj);
        result.v = a.v*float(f0)+b.v*float(f1*sadj);
        result.Normalize();
    }
    return Transformation( result, A.position+(B.position-A.position)*blend );
}