opencv.h

/****************************************************************************************\
*                                  Perspective Transform                                 *
\****************************************************************************************/

template<typename T> static void
perspectiveTransform_( const T* src, T* dst, const double* m, int len, int scn, int dcn )
{
    const double eps = FLT_EPSILON;
    int i;

    if( scn == 2 && dcn == 2 )
    {
        for( i = 0; i < len*2; i += 2 )
        {
            T x = src[i], y = src[i + 1];
            double w = x*m[6] + y*m[7] + m[8];

            if( fabs(w) > eps )
            {
                w = 1./w;
                dst[i] = (T)((x*m[0] + y*m[1] + m[2])*w);
                dst[i+1] = (T)((x*m[3] + y*m[4] + m[5])*w);
            }
            else
                dst[i] = dst[i+1] = (T)0;
        }
    }
    else if( scn == 3 && dcn == 3 )
    {
        for( i = 0; i < len*3; i += 3 )
        {
            T x = src[i], y = src[i + 1], z = src[i + 2];
            double w = x*m[12] + y*m[13] + z*m[14] + m[15];

            if( fabs(w) > eps )
            {
                w = 1./w;
                dst[i] = (T)((x*m[0] + y*m[1] + z*m[2] + m[3]) * w);
                dst[i+1] = (T)((x*m[4] + y*m[5] + z*m[6] + m[7]) * w);
                dst[i+2] = (T)((x*m[8] + y*m[9] + z*m[10] + m[11]) * w);
            }
            else
                dst[i] = dst[i+1] = dst[i+2] = (T)0;
        }
    }
    else if( scn == 3 && dcn == 2 )
    {
        for( i = 0; i < len; i++, src += 3, dst += 2 )
        {
            T x = src[0], y = src[1], z = src[2];
            double w = x*m[8] + y*m[9] + z*m[10] + m[11];

            if( fabs(w) > eps )
            {
                w = 1./w;
                dst[0] = (T)((x*m[0] + y*m[1] + z*m[2] + m[3])*w);
                dst[1] = (T)((x*m[4] + y*m[5] + z*m[6] + m[7])*w);
            }
            else
                dst[0] = dst[1] = (T)0;
        }
    }
    else
    {
        for( i = 0; i < len; i++, src += scn, dst += dcn )
        {
            const double* _m = m + dcn*(scn + 1);
            double w = _m[scn];
            int j, k;
            for( k = 0; k < scn; k++ )
                w += _m[k]*src[k];
            if( fabs(w) > eps )
            {
                _m = m;
                for( j = 0; j < dcn; j++, _m += scn + 1 )
                {
                    double s = _m[scn];
                    for( k = 0; k < scn; k++ )
                        s += _m[k]*src[k];
                    dst[j] = (T)(s*w);
                }
            }
            else
                for( j = 0; j < dcn; j++ )
                    dst[j] = 0;
        }
    }
}