VB Downscaling coordinates - vb.net

Question

I have the need to know when a gdi+ drawn line is clicked on by the mouse.
I have fashioned this function which is used in a loop on all the existing lines and what the function does is:
It makes a buffer of the line's container's size
It makes the whole thing black
It draws the line in green
It gets the pixel at the mouse location
If the pixel is different from black a.k.a green, the line has successfully been clicked and the function should then return true.
This works great, there's no misinterpretations, but I'm afraid that there's a tiny delay (not really noticeable) when my form is in full screen (due to the large buffer).
I'm looking for a way to optimize this, and my first thought is to downscale everything. So what I mean by that is make the buffer like 20x20 and then draw the line in a scaled down version using math. Problem is, I suck at math, so I'm basically asking you how to do this and preferably with an explanation for dummies.
This is the function:
Public Function Contains(ByVal e As Point) As Boolean
Dim Width As Integer = Container.Size.Width
Dim Height As Integer = Container.Size.Height
Dim Buffer As Bitmap = New Bitmap(Width, Height)
Using G As Graphics = Graphics.FromImage(Buffer)
G.Clear(Color.Black)
Dim Start As Point = New Point(ParentNode.Location.X + ParentNode.Size.Width / 2, ParentNode.Location.Y + ParentNode.Size.Height / 2)
Dim [End] As Point = New Point(ChildNode.Location.X + ChildNode.Size.Width / 2, ChildNode.Location.Y + ChildNode.Size.Height / 2)
Dim Control1 As Point
Dim Control2 As Point
Control1.X = Start.X + GetAngle(ChildNode.Location, ParentNode.Location, ChildNode.Location.X - ParentNode.Location.X, ChildNode.Location.Y - ParentNode.Location.Y)
Control1.Y = Start.Y
Control2.X = [End].X
Control2.Y = Start.Y
G.DrawBezier(New Pen(Color.Green, 4), Start, Control1, Control2, [End])
End Using
If Buffer.GetPixel(e.X, e.Y).ToArgb() <> Color.Black.ToArgb() Then
Return True
End If
Return False
End Function
This is one of my attempts to make the function use the idea above:
Public Function Contains(ByVal e As Point) As Boolean
Dim Width As Integer = 20
Dim Height As Integer = 20
Dim Buffer As Bitmap = New Bitmap(Width, Height)
Using G As Graphics = Graphics.FromImage(Buffer)
G.Clear(Color.Black)
Dim Start As Point = New Point(ParentNode.Location.X + ParentNode.Size.Width / 2, ParentNode.Location.Y + ParentNode.Size.Height / 2)
Dim [End] As Point = New Point(ChildNode.Location.X + ChildNode.Size.Width / 2, ChildNode.Location.Y + ChildNode.Size.Height / 2)
Dim Control1 As Point
Dim Control2 As Point
Control1.X = Start.X + GetAngle(ChildNode.Location, ParentNode.Location, ChildNode.Location.X - ParentNode.Location.X, ChildNode.Location.Y - ParentNode.Location.Y)
Control1.Y = Start.Y
Control2.X = [End].X
Control2.Y = Start.Y
G.DrawBezier(New Pen(Color.Green, 4), New Point(Start.X / Width, Start.Y / Height), New Point(Control1.X / Width, Control1.Height / Height), New Point(Control2.X / Width, Control2.Y / Height), New Point([End].X / Width, [End].Y / Height))
End Using
If Buffer.GetPixel(Width, Height).ToArgb() <> Color.Black.ToArgb() Then
Return True
End If
Return False
End Function

Answer 1

Try using a GraphicsPath for drawing and testing with the built-in IsOutlineVisible function:
Public Function Contains(ByVal e As Point) As Boolean
Dim result as Boolean = False
Using gp As New GraphicsPath
gp.AddBezier(your four points)
Using p As New Pen(Color.Empty, 4)
result = gp.IsOutlineVisible(e, p)
End Using
End Using
Return result
End Function
Side note: Bitmaps and Graphic objects need to be disposed when you create them.