rect/line.go

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package rect
import (
"fmt"
"math"
)
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// line is described as two Points
type line struct {
pt1, pt2 Point
}
// determinants aids by calculating necessary values for performing
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// 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
}
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// 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) {
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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")
}
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// 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
}