FcMatrixRotate (3) - Linux Manuals
FcMatrixRotate: Rotate a matrix
NAME
FcMatrixRotate - Rotate a matrix
SYNOPSIS
#include <fontconfig/fontconfig.h>
void FcMatrixRotate (FcMatrix *matrix, double cos, double sin);
DESCRIPTION
FcMatrixRotate rotates matrix by the angle who's sine is sin and cosine is cos. This is done by multiplying by the matrix:
cos -sin sin cos