gg/mx/line.go

package mx

// The type represents a line segment. The name is for short.
type Line [2]Vector
type Lines []Line

// Returns corresponding to the segment Line.
func (l Line) GetLineExpr() LineExpr {
	var (
		x Float
		vertical bool
	)

	p0 := l[0]
	p1 := l[1]
	
	k := (p0.Y - p1.Y) / (p0.X - p1.X)
	c := p0.Y - p0.X*k 
	if p0.X == p1.X {
		x = p0.X
		vertical = true
	}

	return LineExpr{k, c, x, vertical}
}

// Returns the points that the Line contains.
func (l Line) GetContainedPoints(pts Vectors) Vectors {
	ret := make(Vectors, 0, len(pts))
	for i := range pts {
		if l.ContainsPoint(pts[i]) {
			ret = append(ret, pts[i])
		}
	}
	return ret
}

// Check if the edge contains the specified point.
func (l Line) ContainsPoint(p Vector) bool {
	lexpr := l.GetLineExpr()
	if !lexpr.ContainsPoint(p) {
		return false
	}
	
	xMax := Max(l[0].X, l[1].X)
	xMin := Min(l[0].X, l[1].X)
	
	yMax := Max(l[0].Y, l[1].Y)
	yMin := Min(l[0].Y, l[1].Y)
	
	if !(xMin <= p.X && p.X <= xMax) ||
		!(yMin <= p.Y && p.Y <= yMax) {
			return false
	}
	
	return true
}

// Get square of length of line segment (for performance sometimes).
func (ls Line) LenSqr() Float {
	return Sqr(ls[0].X - ls[1].X) +
		Sqr(ls[0].Y - ls[1].Y)
}

// Get length of the line segment.
func (ls Line) Len() Float {
	return Sqrt(ls.LenSqr())
}