basisGradient[0] = -(1.0 - tt) / 2.0;
basisGradient[1] = -(1.0 - tt) / 2.0;
basisGradient[2] = -(1.0 - rr - ss) / 2.0;

basisGradient[3] = (1.0 - tt) / 2.0;
basisGradient[4] = 0.0;
basisGradient[5] = -rr / 2.0;

basisGradient[6] = 0.0;
basisGradient[7] = (1.0 - tt) / 2.0;
basisGradient[8] = -ss / 2.0;

basisGradient[9] = -(1.0 + tt) / 2.0;
basisGradient[10] = -(1.0 + tt) / 2.0;
basisGradient[11] = (1.0 - rr - ss) / 2.0;

basisGradient[12] = (1.0 + tt) / 2.0;
basisGradient[13] = 0.0;
basisGradient[14] = rr / 2.0;

basisGradient[15] = 0.0;
basisGradient[16] = (1.0 + tt) / 2.0;
basisGradient[17] = ss / 2.0;
