code: def _get_zoom_mat(sw:float, sh:float, c:float, r:float)->AffineMatrix:
      "`sw`,`sh` scale width,height - `c`,`r` focus col,row."
      return [[sw, 0,  c],
              [0, sh,  r],
              [0,  0, 1.]f _get_zoom_mat(sw:float, sh:float, c:float, r:float)->AffineMatrix:
      "`sw`,`sh` scale width,height - `c`,`r` focus col,row."
      return [[sw, 0,  c],
              [0, sh,  r],
              [0,  0, 1.]]
docs: `sw`,`sh` scale width,height - `c`,`r` focus col,row.