OffsetPoly
PolyHandle thePoly ; handle leading to Polygon to relocate short distHoriz ; <0 = towards the left, >0 = to the right
short distVert ; <0 = upward, >0 = downward
OffsetPoly modifies a polygon's definition, moving it in any direction on the coordinate plane. Note that this does not have any visible effect on the screen,
until such time as the polygon is drawn or filled.
thePoly is a handle leading to a variable-length Polygon structure. It is typically a value obtained via OpenPoly. distHoriz specifies the horizontal distance, in pixels, to move the polygon.
Positive values move to the right; negative to the left.
distVert specifies the vertical distance, in pixels, to move the polygon.
Positive values move downward; negative upward.
Notes: The polygon retains its shape and size. Use MapPoly to shrink or expand the polygon.
This is an especially efficient operation, since it changes only the value in
the polyBBox field of the Polygon structure; all endpoints that make up the bulk of the data are stored relative to first point.