Struct Polygon

s2/polygon.go:52–81

Polygon represents a sequence of zero or more loops; recall that the interior of a loop is defined to be its left-hand side (see Loop). When the polygon is initialized, the given loops are automatically converted into a canonical form consisting of "shells" and "holes". Shells and holes are both or

//
//   - No loop may be empty. The full loop may appear only in the full polygon.
type Polygon struct {
	loops []*Loop

	// index is a spatial index of all the polygon loops.
	index *ShapeIndex

	// hasHoles tracks if this polygon has at least one hole.
	hasHoles bool

	// numVertices keeps the running total of all of the vertices of the contained loops.
	numVertices int

	// numEdges tracks the total number of edges in all the loops in this polygon.
	numEdges int

	// bound is a conservative bound on all points contained by this loop.
	// If l.ContainsPoint(P), then l.bound.ContainsPoint(P).
	bound Rect

	// Since bound is not exact, it is possible that a loop A contains
	// another loop B whose bounds are slightly larger. subregionBound
	// has been expanded sufficiently to account for this error, i.e.
	// if A.Contains(B), then A.subregionBound.Contains(B.bound).
	subregionBound Rect

	// A slice where element i is the cumulative number of edges in the
	// preceding loops in the polygon. This field is used for polygons that
	// have a large number of loops, and may be empty for polygons with few loops.
	cumulativeEdges []int
}

// PolygonFromLoops constructs a polygon from the given set of loops. The polygon
// interior consists of the points contained by an odd number of loops. (Recall