Find the intersection of two lines: Difference between revisions

=={{header|Visual Basic}}==

{{works with|Visual Basic|5}}

{{works with|Visual Basic|6}}

{{works with|VBA|6.5}}

{{works with|VBA|7.1}}

<lang vb>Option Explicit

Public Type Point

x As Double

y As Double

invalid As Boolean

End Type

Public Type Line

s As Point

e As Point

End Type

Public Function GetIntersectionPoint(L1 As Line, L2 As Line) As Point

Dim a1 As Double

Dim b1 As Double

Dim c1 As Double

Dim a2 As Double

Dim b2 As Double

Dim c2 As Double

Dim det As Double

a1 = L1.e.y - L1.s.y

b1 = L1.s.x - L1.e.x

c1 = a1 * L1.s.x + b1 * L1.s.y

a2 = L2.e.y - L2.s.y

b2 = L2.s.x - L2.e.x

c2 = a2 * L2.s.x + b2 * L2.s.y

det = a1 * b2 - a2 * b1

If det Then

With GetIntersectionPoint

.x = (b2 * c1 - b1 * c2) / det

.y = (a1 * c2 - a2 * c1) / det

End With

Else

GetIntersectionPoint.invalid = True

End If

End Function

Sub Main()

Dim ln1 As Line

Dim ln2 As Line

Dim ip As Point

ln1.s.x = 4

ln1.s.y = 0

ln1.e.x = 6

ln1.e.y = 10

ln2.s.x = 0

ln2.s.y = 3

ln2.e.x = 10

ln2.e.y = 7

ip = GetIntersectionPoint(ln1, ln2)

Debug.Assert Not ip.invalid

Debug.Assert ip.x = 5 And ip.y = 5

LSet ln2.s = ln2.e

ip = GetIntersectionPoint(ln1, ln2)

Debug.Assert ip.invalid

LSet ln2 = ln1

ip = GetIntersectionPoint(ln1, ln2)

Debug.Assert ip.invalid

End Sub</lang>