geom/polygonf.go

package geom

import "log"

// PointsF is a set of points.
type PointsF []PointF

// PolF creates a polygon of points q.
func PolF(q ...PointF) PolygonF { return PolygonF{Points: q} }

// PolygonF is defined by a set of points (floating point).
type PolygonF struct {
	Points PointsF
}

// Add adds q as a vector to all points in p.
func (p PolygonF) Add(q PointF) PolygonF {
	var r = p.copy()
	for i, pt := range r.Points {
		r.Points[i] = pt.Add(q)
	}
	return r
}

func (p PolygonF) copy() PolygonF {
	var q = PolygonF{make(PointsF, len(p.Points))}
	copy(q.Points, p.Points)
	return q
}

// Extend creates a new polygon based on p with one or more extra points q.
func (p PolygonF) Extend(q ...PointF) PolygonF {
	var t = PolygonF{make(PointsF, len(p.Points)+len(q))}
	copy(t.Points, p.Points)
	copy(t.Points[len(p.Points):], q)
	return t
}

// Mul multiplies the points of polygon p with t and returns the result.
func (p PolygonF) Mul(t float64) PolygonF {
	var q = p.copy()
	for i, pt := range q.Points {
		q.Points[i] = pt.Mul(t)
	}
	return q
}

// Triangulate triangulates the polygon p.
func (p PolygonF) Triangulate() []TriangleF {
	var triangles []TriangleF
	points := p.copy().Points[:]
	n := len(points)

	if n > 0 && points[0] == points[n-1] { // remove first point if polygon is closed
		points = points[1:]
		n--
	}

	triangle := func(i int) TriangleF {
		return TrF(points[(i+n-1)%n], points[i], points[(i+1)%n])
	}
	ear := func(i int) (TriangleF, bool) {
		t := triangle(i)
		if t.Winding() == WindingCounterClockwise {
			return TriangleF{}, false
		}
		for j := 0; j < n-3; j++ {
			p := points[(i+2+j)%n]
			if t.Contains(p) {
				return TriangleF{}, false
			}
		}
		return t, true
	}

	for n >= 3 {
		leastSharp := -1
		var leastSharpAngle float64
		for i := range points {
			if t, ok := ear(i); ok {
				sharpAngle := t.SmallestAngle()
				if leastSharp < 0 || sharpAngle > leastSharpAngle {
					leastSharp = i
					leastSharpAngle = sharpAngle
				}
			}
		}
		if leastSharp < 0 {
			if n >= 3 {
				log.Println("not fully triangulated")
			}
			break
		}
		triangles = append(triangles, triangle(leastSharp))
		points = append(points[:leastSharp], points[leastSharp+1:]...)
		n = len(points)
	}
	return triangles
}

// Reverse reverses the order of the points of polygon p.
func (p PolygonF) Reverse() PolygonF {
	n := len(p.Points)
	var q = PolygonF{make(PointsF, n)}
	for i := 0; i < n/2; i++ {
		q.Points[i], q.Points[n-i-1] = p.Points[n-i-1], p.Points[i]
	}
	return q
}