Constant opencv::imgproc::CHAIN_APPROX_NONE

pub const CHAIN_APPROX_NONE: i32 = 1;

stores absolutely all the contour points. That is, any 2 subsequent points (x1,y1) and (x2,y2) of the contour will be either horizontal, vertical or diagonal neighbors, that is, max(abs(x1-x2),abs(y2-y1))==1.