// obtain the direct homography from the current configuration
static void obtain_current_homography(double H[3][3], struct viewer_state *e)
{
double C[4][2];
for (int p = 0; p < 4; p++)
map_view_to_window(e, C[p], e->c[p]);
homography_from_eight_points(H,
C[0], C[1], C[2], C[3],
e->p[0], e->p[1], e->p[2], e->p[3]
);
}
// compute the homography given by the images of four points
static void compute_homography_from_point_pairs(double H[3][3],
float from[4][2], float to[4][2])
{
double f[4][2], t[4][2];
for (int i = 0; i < 4; i++)
for (int j = 0; j < 2; j++) {
f[i][j] = from[i][j];
t[i][j] = to[i][j];
}
homography_from_eight_points(H, f[0], f[1], f[2], f[3],
t[0], t[1], t[2], t[3]);
}
