UserControl/ElementHost Transparent Background - wpf

Question

I need a method that sets the background of the ElementHost completely transparent or so that it does not even render in the first place.
Current Structure
In the background I have a PictureBox.
Over that there is my UserControl (Which you can Download below).
Both the PictureBox and the UserControl have a Width of 150.
As you can see in the Picture above, the UserControl is 100% Invisible.
In the UserControl is an ElementHost with a Width of 120, within that there is a WPF-Content with a Width of 100.
Everything is Transparent, except the ElementHost1.
My Code
UserControl:
Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
Get
Dim cp As CreateParams = MyBase.CreateParams
cp.ExStyle = &H20
Return cp
End Get
End Property
Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
End Sub
Public Overrides Sub Refresh()
Parent.Invalidate(New Rectangle(Me.Location, Me.Size), True)
End Sub
Public Sub New()
InitializeComponent()
Me.SetStyle(ControlStyles.SupportsTransparentBackColor, True)
Me.BackColor = System.Drawing.Color.Transparent
ElementHost1.BackColor = System.Drawing.Color.Transparent
ElementHost1.BackColorTransparent = True
End Sub
I´ve also tried to create a Custom ElementHost:
Public Class TransElementHost
Inherits ElementHost
Public Sub TransElementHost()
Me.SetStyle(ControlStyles.SupportsTransparentBackColor, True)
Me.BackColorTransparent = True
'Me.BackColor = System.Drawing.Color.FromArgb(0, 0, 0, 0)
End Sub
Protected Overrides ReadOnly Property CreateParams() As System.Windows.Forms.CreateParams
Get
Dim cp As CreateParams = MyBase.CreateParams
cp.ExStyle = &H20
Return cp
End Get
End Property
Protected Overrides Sub OnPaintBackground(ByVal e As System.Windows.Forms.PaintEventArgs)
End Sub
Public Overrides Sub Refresh()
Parent.Invalidate(New Rectangle(Me.Location, Me.Size), True)
End Sub
End Class
My SVGTest-UserControl
Does anybody have an idea?

Answer 1

I know it's been really long since this was active, but if you still need it I've (finally) got a code that will draw controls' backgrounds fully transparent.
Just put this code in the control's code. It overrides the OnPaintBackground event:
Protected Overrides Sub OnPaintBackground(e As System.Windows.Forms.PaintEventArgs)
MyBase.OnPaintBackground(e)
If Parent IsNot Nothing Then
Dim index As Integer = Parent.Controls.GetChildIndex(Me)
For i As Integer = Parent.Controls.Count - 1 To index + 1 Step -1
Dim c As Control = Parent.Controls(i)
If c.Bounds.IntersectsWith(Bounds) AndAlso c.Visible = True Then
Dim bmp As New Bitmap(c.Width, c.Height, e.Graphics)
c.DrawToBitmap(bmp, c.ClientRectangle)
e.Graphics.TranslateTransform(c.Left - Left, c.Top - Top)
e.Graphics.DrawImageUnscaled(bmp, Point.Empty)
e.Graphics.TranslateTransform(Left - c.Left, Top - c.Top)
bmp.Dispose()
End If
Next
End If
End Sub

Answer 2

It's probably not the best fix, but you could try using the ButtonRenderer class. Put this code either in OnPaintBackground or OnPaint.
If Me.BackColor = Color.Transparent Then
Windows.Forms.ButtonRenderer.DrawParentBackground(e.Graphics, Me.ClientRectangle, Me)
End If
The ButtonRenderer class is used to draw the regular buttons; their border, background, text, image etc.
I used the above code myself to create a custom control with transparent background. (Though I see now that my control inherits from ButtonBase... But the above code is still worth a try).