/**
* Rotates a shape 180 degrees around the edge shared by the two given points.
*
* The two points must be neighbors.
*/
public static IEnumerable <FlatHexPoint> Rotate180About(
IEnumerable <FlatHexPoint> shape,
FlatHexPoint p1,
FlatHexPoint p2)
{
var translation = p1.Translate(p2);
var correction = translation.Subtract(translation.Rotate180()).ScaleDown(2);
return(TransformShape <FlatHexPoint>(shape, point => point.Rotate180().Translate(correction)).ToList());
}
/**
* Rotates a shape 120 degrees around the vertice shared by the three given points.
*
* The three points must form a close triangle (they must share a vertex).
*/
public static IEnumerable <FlatHexPoint> Rotate120About(
IEnumerable <FlatHexPoint> shape,
FlatHexPoint p1,
FlatHexPoint p2,
FlatHexPoint p3)
{
/*
* If t = (p1 + p2 + p3)/3, then the result is p => (p - t).Rotate120() + t.
*
* This can be rewritten p => p.Rotate120() - t.Rotate120() + t
* = p.Rotate120() (T - T.Rotate120())/3,
* where T = p1 + p2 + p3.
*
* This is what this method calculates. This is done so that all coordinates in
* intermediatary calculations stay integers.
*/
var translation = p1.Translate(p2.Translate(p3));
var correction = translation.Subtract(translation.Rotate120()).ScaleDown(3);
return(TransformShape(shape, point => point.Rotate120().Translate(correction)).ToList());
}