Offset origin

The origin of the coordinate system (relative to the upper left corder of this render object) in which to apply the matrix.

Setting an origin is equivalent to conjugating the transform matrix by a translation. This property is provided just for convenience.

Source 

Offset get origin => _origin;
void origin=(Offset newOrigin)

Source 

set origin (Offset newOrigin) {
  if (_origin == newOrigin)
    return;
  _origin = newOrigin;
  markNeedsPaint();
}