Private Type VECTOR
    x As Double
    Y As Double
End Type

Private Type NewLine
    a As VECTOR
    b As VECTOR
    
    MinX As Double
    MinY As Double
    MaxX As Double
    MaxY As Double
End Type

Dim Vor As Long
Dim Vox As Long
Dim Lines() As NewLine
Dim PI As Double
Dim Eject As Boolean
Dim DirX As VECTOR
Dim InitDir As VECTOR
Private Sub DrawLine(ByRef a As VECTOR, ByRef b As VECTOR)
    Line (a.x, a.Y)-(b.x, b.Y)
End Sub
Function ToDeg(ByVal a As Double) As Double
    ToDeg = a * (180 / PI)
End Function
Private Function Subtract(ByRef a As VECTOR, ByRef b As VECTOR) As VECTOR
    Subtract.x = a.x - b.x
    Subtract.Y = a.Y - b.Y
End Function
Private Function Normalize(ByRef a As VECTOR) As VECTOR
    On Error GoTo catcher
    Normalize.x = a.x / Length(a)
    Normalize.Y = a.Y / Length(a)
    
    Exit Function
catcher:
    Normalize.x = 0
    Normalize.Y = 0
End Function
Private Function Length(ByRef a As VECTOR) As Double
    Length = a.x ^ 2 + a.Y ^ 2
    Length = Length ^ 0.5
End Function
Private Function Dot(ByRef a As VECTOR, ByRef b As VECTOR) As Double
    On Error GoTo reeeh
    Dot = (a.x * b.x) + (a.Y * b.Y)
    Dot = Dot / (Length(a) * Length(b))
    
    Exit Function
reeeh:
    Dot = 0
End Function
Private Function Mul(ByRef a As VECTOR, ByVal b As Double) As VECTOR
    Mul.x = a.x * b
    Mul.Y = a.Y * b
End Function
Function Delta(ByVal a As Double, ByVal b As Double) As Double
    Delta = a - b
End Function
Function Clamp(ByVal a As Double, ByVal b As Double, ByVal c As Double) As Double
    Clamp = a
    
    If Clamp < b Then Clamp = b
    If Clamp > c Then Clamp = c
    
End Function

Private Sub Check1_Click()
    Cls
    AutoRedraw = Not AutoRedraw
    Command1_Click
End Sub

Private Sub Command1_Click()
    Eject = True
    Form_Activate
End Sub
Private Sub Command2_Click()
    Eject = True
    Form_Load
    Command1_Click
End Sub
Private Sub Form_Activate()
    Eject = False
    Dim lastimpact As VECTOR
    Dim x As Double
    Dim Y As Double
    Dim x1 As Double
    Dim y1 As Double
    Dim firstbounce As Boolean
    
    Randomize
    
    Cls
    Y = Height / 30
    x = 1
    
    moveamt = 1
    
    lastx = x
    lasty = Y
    
    DirX = InitDir
    
    lastimpact.x = 1
    lastimpact.Y = Y
    
    ForeColor = vbBlack
    For i = 1 To UBound(Lines)
        DrawWidth = 10
        Call DrawLine(Lines(i).a, Lines(i).b)
    Next i
    
    DrawWidth = 1
    ForeColor = vbRed
    
    PT = Point(0, 0)
    
    Dim eaz As Integer

    Do While True
meep:
        eaz = eaz + 1
        Dim impact As VECTOR
        
        impact.x = x
        impact.Y = Y
        DoEvents
        
        x1 = x + DirX.x * moveamt
        y1 = Y + DirX.Y * moveamt
        
        PT = Point(x1, y1) <> vbBlack
        
        If Not PT Then
            Dim pos As VECTOR
            pos.x = x1
            pos.Y = y1
            
            pos = Normalize(Subtract(pos, lastimpact))
            
            'Pos is the normal of the segment between the current point and where
            'it last bounced
            
            'DirX is the current directional vector that desribes the segment
            
            'In the end, I was searching for the entirely wrong thing.
            'What I was searching for was the programming term for the object,
            'when what I really needed was Projecting Vectors and a few other
            'related things.
            
            'Many thanks to 8lank and Cakes for pointing me in the right direction.
            
            i = IsOnLineLong(impact)
            
            If i >= 1 Then
            
                Dim wall As VECTOR
                Dim vel As VECTOR
                Dim lnm As VECTOR
                Dim a As VECTOR
                Dim b As VECTOR
                Dim proj1 As VECTOR
                Dim proj2 As VECTOR
                Dim dp1 As Double
                Dim dp2 As Double
                
                vel = Subtract(impact, lastimpact)
                
                a.x = Lines(i).MinX
                a.Y = Lines(i).MinY
                
                b.x = Lines(i).MaxX
                b.Y = Lines(i).MaxY
                
                wall = Subtract(b, a)
                
                lnm.x = wall.Y
                lnm.Y = -wall.x
                
                dp1 = Dot(vel, wall)
                
                proj1 = Mul(wall, dp1)
                
                dp2 = Dot(vel, lnm)

                proj2 = Mul(Normalize(lnm), dp2)
                
                DirX = Subtract(Normalize(Subtract(proj1, Mul(proj2, -1))), pos)
                
                DirX.x = Clamp(DirX.x, -1, 1)
                DirX.Y = Clamp(DirX.Y, -1, 1)
                
                If Length(Subtract(impact, lastimpact)) < 1 Then
                    'Got stuck
                    DirX = Mul(DirX, -1)
                End If
                
                lastimpact.x = x
                lastimpact.Y = Y
                
            End If
        End If
        
        x = x + DirX.x * moveamt
        Y = Y + DirX.Y * moveamt
        
        Line (lastx, lasty)-(x, Y)
        
        lastx = x
        lasty = Y
        
        If x < 0 Or x > Width / 15 Or Y < 0 Or Y > Height / 15 Or Eject Then
            Eject = True
            Exit Do
        End If
        
        If eaz < 400 Then
            GoTo meep
        Else
            eaz = 0
        End If
    Loop
End Sub

Private Sub Form_Load()
    ReDim Lines(0 To 0)
    
    PI = Atn(1) * 4
    
    DirX.x = 1
    DirX.Y = -1 + Rnd * 2
    
    InitDir = DirX
End Sub

Private Sub Form_MouseDown(Button As Integer, Shift As Integer, x As Single, Y As Single)
    Vor = x
    Vox = Y
    Circle (Vor, Vox), 1
End Sub

Private Sub Form_MouseUp(Button As Integer, Shift As Integer, x As Single, Y As Single)
    On Error GoTo catch
    
    If Delta(Vor, x) = 0 Or Delta(Vox, Y) = 0 Then
        Exit Sub
    End If
    ReDim Preserve Lines(0 To UBound(Lines) + 1)
    Lines(UBound(Lines)).a.x = Vor
    Lines(UBound(Lines)).a.Y = Vox
    Lines(UBound(Lines)).b.x = x
    Lines(UBound(Lines)).b.Y = Y
    
    If Vor < x Then
        Lines(UBound(Lines)).MinX = Vor
        Lines(UBound(Lines)).MaxX = x
    Else
        Lines(UBound(Lines)).MinX = x
        Lines(UBound(Lines)).MaxX = Vor
    End If
    
    If Vox < Y Then
        Lines(UBound(Lines)).MinY = Vox
        Lines(UBound(Lines)).MaxY = Y
    Else
        Lines(UBound(Lines)).MinY = Y
        Lines(UBound(Lines)).MaxY = Vox
    End If
    
    Circle (x, Y), 1
    Line (Vor, Vox)-(x, Y)
    
    Exit Sub
catch:
    ReDim Preserve Lines(0 To UBound(Lines) - 1)
End Sub
Private Function IsOnLineQuick(ByRef PT As VECTOR, ByVal i As Long) As Boolean
    IsOnLineQuick = False
    
    If Clamp(PT.x, Lines(i).MinX, Lines(i).MaxX) = PT.x And Clamp(PT.Y, Lines(i).MinY, Lines(i).MaxY) Then
        IsOnLineQuick = True
    End If
End Function
Private Function IsOnLineLong(ByRef PT As VECTOR) As Long
    Dim i As Long
    
    For i = 1 To UBound(Lines)
        If IsOnLineQuick(PT, i) Then
            'Could be on the line, filter out ones that it can't be on.
            'Simple InBox test
            
            'If the dot product of the current point between the minumum and maximum
            'of the tested line is within a tenth of 1 ( when it's usually within .0001 when corect )
            ', then it's corect. This is similar to the function guesser that TI8*'s have
            'That shows an r=X, and the closer X is to 1, the generally closer it is
            
            'I just guessed at this method and was surprised it even worked ^_^
            
            If (Dot(PT, Lines(i).a) + 0.1) \ 1 = 1 Then
                If (Dot(PT, Lines(i).b) + 0.1) \ 1 = 1 Then
                    IsOnLineLong = i
                    Exit For
                End If
            End If
        End If
    Next i
End Function
Private Sub Form_Unload(Cancel As Integer)
    Eject = True
End Sub