static void SetSinCos(ref SKMatrix matrix, float sin, float cos, float pivotx, float pivoty)
{
float oneMinusCos = 1 - cos;
matrix.scaleX = cos;
matrix.skewX = -sin;
matrix.transX = sdot(sin, pivoty, oneMinusCos, pivotx);
matrix.skewY = sin;
matrix.scaleY = cos;
matrix.transY = sdot(-sin, pivotx, oneMinusCos, pivoty);
matrix.persp0 = 0;
matrix.persp1 = 0;
matrix.persp2 = 1;
#if OPTIMIZED_SKMATRIX
matrix.typeMask = Mask.Unknown | Mask.OnlyPerspectiveValid;
#endif
}