MBitmapOrigin BitmapNumber.w,XOffset.w,YOffset.w ; Set origin of Bitmap

Sets the handle for a previously-created chunky Bitmap object. This is the
coordinate offset that is added to the coordintes that you may specify for a
blit-operation later on, but is more likely to be used in conjunction with
Mildred's wrapping feature to provide the offset of a sliding window relative to
the Bitmap's image and/or stencil.