Shrink a Polygon as an Array of TPoint?

Question

I'm utilizing TCanvas.Polygon() and would like to know how I can go about shrinking the size of the polygon, either if there is already a function for this, or how to write one. I have a type declared TPoints: Array of TPoint; and using it when calling TCanvas.Polygon().

The trouble is, if I have to write this function, how does it recognize which direction each point needs to move (based on proportion to the rest of the polygon)?

For example, if I made an array of points (TPoints) to represent a 5 pointed star, and I needed to shrink it by 2 pixels, how would it know the direction to move the points?

The end intention is to implement a gradient for a polygon. There will be a loop to perform this, in which a) color is slightly adjusted, b) polygon points need to shrink by a few pixels, and c) polygon gets drawn (smaller than the previously drawn one); thus, creating a gradient.

Answer 1

It seems to me you're looking for a way to do polygon offsetting - shrinking or expanding polygons by a specified number of units (pixels). My Clipper Library (written in Delphi, C++ and C#) does polygon offsetting. The 'direction the points move' (ie shrinking or expanding) will depend on the sign (positive vs negative) of the supplied 'delta' parameter to the OffsetPolygons function.