package rect import ( "fmt" "math" ) // line is described as two Points type line struct { pt1, pt2 Point } // determinants aids by calculating necessary values for performing // calculations using the determinant of two points func determinants(l line) (float64, float64, float64) { a := l.pt2.Y - l.pt1.Y b := l.pt1.X - l.pt2.X c := a*l.pt1.X + b*l.pt1.Y return a, b, c } // lineIntersection returns the Point of intersection between two lines. // lineIntersection will only return a point if the point lies on the // line, otherwise it will return a nil point and an error func lineIntersection(l1, l2 line) (Point, error) { a1, b1, c1 := determinants(l1) a2, b2, c2 := determinants(l2) det := a1*b2 - a2*b1 if det != 0 { x := ((b2*c1 - b1*c2) / det) y := ((a1*c2 - a2*c1) / det) minx1, maxx1 := math.Min(l1.pt1.X, l1.pt2.X), math.Max(l1.pt1.X, l1.pt2.X) miny1, maxy1 := math.Min(l1.pt1.Y, l1.pt2.Y), math.Max(l1.pt1.Y, l1.pt2.Y) minx2, maxx2 := math.Min(l2.pt1.X, l2.pt2.X), math.Max(l2.pt1.X, l2.pt2.X) miny2, maxy2 := math.Min(l2.pt1.Y, l2.pt2.Y), math.Max(l2.pt1.Y, l2.pt2.Y) if minx1 <= x && x <= maxx1 && miny1 <= y && y <= maxy1 { if minx2 <= x && x <= maxx2 && miny2 <= y && y <= maxy2 { return Point{x, y}, nil } } } return Point{}, fmt.Errorf("lines do not intersect") } // lineOnLine determins if both points of a line, l1, are on the same line, l2 func lineOnLine(l1, l2 line) bool { if onLine(l1.pt1, l1.pt2, l2.pt1) && onLine(l1.pt1, l1.pt2, l2.pt2) { return true } return false }